Flushing Your Imperial's Cooling System


Imperial Home Page -> Repair -> Cooling System -> Flushing

Some important facts to remember when flushing your cooling system:


Anti-freeze contains a lot of chemicals that do more than protect your cooling system from freezing. Most good brand name anti freeze products contains anti-corrosive chemicals which are especially important to engines that contain aluminum parts. Therefore it is a good idea to flush out the coolant each season or at least every other season and replace the anti freeze to gain the protection from the new fluid.

Most engines have drain plugs on the block so that you can ensure that you drain all of the old coolant. these plugs are usually very hard to get to as they are hidden behind the exhaust system and other components on the engine. As a result most people don't drain the block. If you want to make sure you get all the old stuff out you can flush the system with cold water, then run the engine until the thermostat opens (feel the top hose and run until it gets hot) and then shut it off and drain it again. If you do this a few times you will basically remove all the old coolant by a dilution process.

Now comes the rub. You have pure water remaining in the heater core and the block so how much anti freeze should you add to ensure that you get the correct mixture (50-50) ? Look in your owner's manual and find out the capacity of your cooling system. For example let's assume your system holds 8 quarts. The simple answer to the question is just add 4 quarts of anti freeze and then top it off with water. But what happens if you can't fit 4 quarts in the system due to the amount left in the block and heater core??

Here's the trick. On the last draining, drain the coolant into a drain pail and measure the amount of liquid you were able to remove. Let's assume you could only get out five quarts - that means there are three quarts of pure water left in the cooling system. In order to ensure that you have a 50-50 mixture of coolant you need to add an equal amount of anti freeze so just add 3 quarts of anti freeze to the system. Now you have 6 quarts of 50-50 mixture in the system. In order to make up the difference just add 2 quarts of 50-50 mix (one quart of water and one quart of anti freeze) to the cooling system and it will be topped off with the correct mixture of anti freeze and water.

Question from Joseph:


My 1974 LeBaron is overheating (has a completely rebuilt coolant system along with temp. sender and gauge). About a month ago the car started overheating.  My Chrysler/Plymouth dealership is clueless (these guys are normally really good). The Service Manager (John - who I really believe walks on water -- real nice guy) has sent (at his cost) the LeBaron to a coolant specialist who is stumped on why the car is overheating. Do you have any ideas? 




From Frank:


1) Check that the gauge and sending unit are accurate. 

Potential problems: 

A) Voltage limiter B) Gauge C) Sending unit D) Wiring E) Ground connection (screwing the sender into the block grounds it - too much Teflon tape insulates it.) 

Try one of these: a) Putting a direct reading mechanics gauge into the temp sensor position b) Putting a temporary gauge into the top of the radiator tank c) Run until nearly "overheated" and place a surface temp gauge on the top radiator tank to confirm temperature Assuming that the engine is truly overheating. 

2) Replace thermostat in upper radiator hose 

3) Replace lower radiator hose making certain that the metal "spring" inside the hose is present and runs from end-to-end. 

4) Flush the engine block to remove any sediment

5) Remove, flush, and boil out the radiator 

6) Reverse flush the heater core, to remove the last traces of sediment. 

7) Set ignition timing - verify that the timing plate (what the pickup coil in the distributor mounts on) is secure. 

8) Check vacuum advance for proper operation 

9) Check distributor centrifugal advance for proper operation 

10) Check for stuck/frozen shut exhaust valve heat riser valve. 


1) Verify the symptoms. Yes, the parts were replaced, but suspect everything unless you KNOW otherwise. New parts can be bad. 

2) A stuck thermostat will cause overheating 

3) The spring prevents the water pumps suction from collapsing the hose, shutting off the cooler return water from the radiator 

4,5,6) Junk in the cooling system can impair efficiency to the point that the system barely cools. (Personal experience) 

7,8,9) Retarded ignition timing raises temperatures. Does the engine ping a lot? If so the timing may be too far advanced. 

10) The heat riser on the right exhaust manifold closes when the engine is cold, sending hot exhaust from the right bank, through the cross-over in the intake manifold, which warms it, and out through the left exhaust manifold. If stuck, the engine works too hard to breath, which raises temperatures and also makes the intake manifold very hot. Guess where the coolant temperature sensor is mounted?


From Pete:


Seems to me that if the cooling system is functioning properly (radiator, hoses, water pump), then you might have a blown head gasket or cracked head. I had a similar situation with my 84 Chevy truck. Entire cooling system replaced w/new parts. No oil in the coolant or coolant in the oil. It would even overheat with the thermostat removed. Finally I remove the engine and had the head fluxed. Sure enough....cracks in the head. Combustion gases going directly into the coolant.

Question from Rob:


Remember when I said that I didn't want to be on the side of the road with the hood up for all to see, steam sizzling from everywhere? Well ... Tonight I got close. Hissed into a gas station about 10 blocks from my house, almost no time driving at all, steaming from the lower radiator hose.   I'm trying to figure out what the hell has gone wrong with my car.  I pulled the hose connecting the water pump/thermostat and the radiator. Pushed a screwdriver into the thermostat to check the movement; there was almost none. Without the proper tool to pull the housing and thermostat completely, I had to take a hammer and pop a couple of holes in the thermostat so there would be some flow, put the hose back on, refill the radiator and get home. Well, I did, and it worked, but not before discovering something almost sickening: It turns out that all day yesterday she was running over-hot, and losing coolant (I couldn't tell because the new voltage regulator I got is screwy, it makes the gauges fluctuate too much to get a true reading, and we were traveling fast enough not to notice any steam coming from under the car). I poured two gallons of anti-freeze and two gallons of water into her before she got back to level. YIKES!!!! That's a loss of a full quarter coolant capacity. Man, that could have been BAD. No wonder tonight she overheated immediately. I'm just glad I was paying attention today, and that we made it home yesterday. My guess is that three things are working against me: bad pumps (water and oil), stuck thermostat, and engine crud. The pumps are easy, as is the thermostat, but engine crud worries me. Considering the state the seals were in, I have to have some crud. But I haven't the faintest notion (nor the required time and space) of how to pull major pieces of the engine off.




From Bill:


I really would try a good radiator flush first, couple of times. It is the cheapest and the cleanest. I have had good luck getting a lot of the crud out that way. The way I do it is to remove thermostat so the flow is not restricted. Use flush according to directions. Drain after flushing by removing lower radiator hose, so big junk can get out. Repeat again. Replace with new thermostat and 50/50 mix anti freeze and water. I really doubt that your water pump is bad. Usually when they go you will hear the bearing or it will leak. I bet the stuck thermostat was your problem all along!


From Bruno:


While you are at it, go for a high flow thermostat with a larger valve in it. Robert Shaw makes it. And use a Flow Kooler high volume pump.


From Ken:


Let's see.....I agree here, but I think you said you have a new radiator core, so......... I would back-flush the engine, pressure/water into the top of the engine, thermostat housing, then out below, disconnect lower radiator hose so gunk does not go into the new radiator. My '49 truck shop manual suggests this, I don't know if there is a factory procedure for 1960. Sounds like you might have gotten a bum-thermostat, won't that be nice?? (if that's the problem) Or is that the old thermostat? Whatever......put in another one and maybe you'll be running too cool. I agree that if the pump was "bad", it would leak or the bearings would be bad, but otherwise I'm not sure how it would fail to pump water unless there is some way the impeller could be spinning on the shaft, and I don't know if that's possible. Never heard of that. Don't know about the big block, but the small block actually uses several different pumps, same pump but having a different number of impeller blades depending on application. Other good suggestion I saw was to be very sure the lower radiator hose is not collapsing.

Question from Dave:


Here is a curiosity I haven't before encountered. In the overflow bottle of my 1973 Imperial, there is a large amount of sludge clinging to the overflow tube and the sides of the bucket. The sludge has a light brown, crumbly appearance, is slippery to the touch like wet clay, and has no grit. What could it be? I suspect this substance may be a symptom or cause of my Imperial's running a little hot lately (no boil over or burst hoses, however). Any suggestions for radiator/cooling system flush products? Of course, I will remove my AutoTemp II servo before flushing.




From Bob:


I've cleaned out several overflow bottles in the last few years and found "glop" in all of them. Who knows what it is? Who cares? It cleaned up OK. When I flushed out my Imp's system 2 years ago, I used a Prestone flush product. Put it in, run the car a while, drain the water. Repeat. Repeat! The system was draining fairly clean. I filled it with the new formula coolant, Havoline Dex-Cool. It's supposed to be more corrosion resistant and "long-life". The car has been running cool ever since, knock on wood...


From Chris:


I have found this gray sludge every time I've either re-cored a radiator or flushed the cooling system of an older or long-dormant car. I suspect that it is the accumulation of the deposits from throughout the cooling system, especially the engine block, that suddenly come into the overflow bottle when clean new coolant is introduced and the system runs a little freer. I find that a thorough engine and cooling system flush, sometimes again after another 500 miles, removes most of the sludge.

Question from David:


I have noticed that the there is a white foam in my oil.  The last time I flushed my radiator, I used one bottle of Prestone Radiator Flush according to the directions. I  flushed the radiator beyond what the directions called for. Oil seems fine, both level and appearance. When cold, water it is clear. Foam is very white in color.




From Brad:


How much water pump lube did you add when you flushed-and-filled? Too much of the lube will cause foaming.


From Doug:


I have seen it before and it was oil getting in from a head gasket.  Does the foam fill oily and how bad is it.  Hopefully its just from the flush.  When it's cold, look in the radiator to see if the fluids look abnormal and keep an eye on the color of the oil.


From Dick:


Another source of oil contamination in the oil can be the transmission cooler. Sometimes this will seep into the coolant. Check your transmission fluid for appearance and level. If this leak gets bad enough, it will increase the pressure in the radiator enough to cause a leak or even a burst of a seam, so you need to find this before there is more damage. Oil in the water won't hurt the engine, but water in the oil, either in the transmission or engine, will cause a lot of damage, and pretty quickly. If you suspect this may be the culprit, disconnect the cooler lines at the bottom of the radiator. and pressurize the cooler n to 15 PSI or so, then check inside the top tank for bubbles coming up through the radiator core. Any at all is reason to replace or repair the radiator, quick like a bunny! It is OK to drive the car for a while with the cooler lines bypassed with a fuel grade (SAE 30R9) hose, held tight to the ends of the lines with screw type hose clamps, but don't tow any house trailers that way.



Is antifreeze necessary in your radiator after it is flushed?


Reply from 4-toes:


Antifreeze is necessary, not just to prevent freezing, but it raises the boiling point of the coolant. The radiator cap is also important. It must maintain the proper pressure in the system as this also raises the boiling point. The first thing I would check would be the specific gravity (with an antifreeze tester) and the pressure cap (with a cap tester). The required cap pressure for your specific car is available at any parts store. Both of these testers would be available at any full service gas station, or inexpensively from your favorite auto parts store. If the system is cooling properly when the car is running you should not have a cool down problem.

Question from Wayne:


I took Victoria (72 LeBaron) to check out the "Mopar Mini-Nationals" held  over the weekend. Anyway, it was like a gazillion degrees outside, and on the way there and back, although she did not boil over, her heat gauge was at the top of the line, just below the "H". It was especially bad on the freeway at freeway speeds. Like I said, she didn't boil over, nor did the "check gauges" light come on, nor did it make it all the way to "H", but it was  hotter than I was comfortable with. I checked her fluid level when cool, and  it was full, so, do I have a problem or is it just too d***m hot?


Reply from Dick:


My guess would be that your cooling system is getting close to the margin. When these cars were new, they ran very cool in any weather. My 68 takes a family of 6 to Las Vegas in temps over 115, across the I-15 and in Las Vegas city traffic, with the AC keeping everyone comfortable (only complaint I ever get is from the right front seat, my wife, who likes it warmer than the rest of us, and I have to remind her that her AC outlet is individually controllable as to direction and volume). Under these conditions, the dash gauge never shows more than the first 1/3 of the normal range. My radiator has been rodded out, and I have cleaned out the block passages thoroughly when I was replacing the core plugs. The cooling systems on the 440s are designed with so much extra cooling capacity that they have to get REALLY plugged up before there is any indication on the gauge. Inspect the tops of the tubes with a small flashlight and mirror, you will probably see stuff collected in the top tank You will have to drain enough coolant so you can see the metal "floor" of the tank. If you see crud, then your first and cheapest bet is to pull the radiator yourself, and flush it with copious quantities of water from the garden hose (don't let the water pressure build up in the radiator, though). Be sure to plug off the transmission cooler fittings so you don't get any water in there! The way I do this is: put the cap on, turn the radiator upside down, cover the upper hose connection with one hand (meaning the connection into the "top" tank, which is now on the ground) and fill the radiator by pouring water from the hose into the "bottom" hose connection. When it is full to overflowing, quickly pull your hand off the "top" hose connection and observe what runs out. If you see particles of crud, you've fixed at least part of your problem. Repeat until it runs clean, or dinner time, whichever occurs first. It's a judgment call as to whether or not you've gotten it truly clean enough. If you want to be sure, take it to your local friendly radiator shop and have it "rodded out" and flow checked. If your car only seems to run hot at freeway speed, verify that the spring is still in the lower hose. Many "modern" mechanics don't believe in these, but then they haven't studied physics, usually.

Question from Tim (1962): 


Can anyone tell me what the correct thermostat temperature setting is for a '62 413cui.  The one in the car is 180 but the car is running really hot. Car also has a 15lb radiator cap. 


Reply from John:


It sounds like you need a real good engine flush and or radiator rebuild--- after that many years those radiators and heater cores can get really plugged up....

Question from Dan (1981): 


Two months ago, I was driving down the Interstate when steam bursts into the passenger compartment through the ac vents.  I pulled over to the shoulder and soon ascertained that the car had overheated and that the heater core had blown.  There was never any idiot light warning. After it
cooled, I rerouted the heater hoses to bypass the core, limped to the next exit, filled the radiator and limped home.  I was still losing coolant from
around the water pump gasket.

Fast forward to yesterday.  I completed installing a new water pump, hoses, belts, the power steering pump & hoses.  I took it on a shakedown cruise only to discover that the car overheats severely after traveling only a few
miles.  When the engine is turned off, you can hear a violent boiling of the coolant from the engine.

I replaced the radiator cap.  No difference.

I changed the thermostat, replacing the 180 with a 160 degree.  No change.

I thought perhaps the coolant wasn't circulating, but everything is hot, i.e. hoses, radiator, engine.

I tore it apart again to inspect the replacement water pump.  Was it perhaps not an exact replacement?  Was the impeller mounted backwards? No such luck. As far as I can tell, its identical to the old one.

So, what's the cause of the overheating?  My original theory was that I had been unaware of a leak and that the coolant level dropped causing it to
overheat and resulting in the damage to the heater core and water pump gasket.

My new theory is whatever caused the overheating happened 2 months ago on the Interstate and its still with me today. I see no evidence of oil mixing with water, or water in the oil.  The car runs fine, as long I don't go further than 5  miles.



From Dick:


First thing is probably to verify that the idiot light sender and wiring is OK. If you pull off (upwards) the wire that goes to the sender (it is right under the AC compressor, and a bear to get at, you will need needle nose pliers and a good flashlight to do this) then ground the end of the wire to something reliably ground, like the ground post on the alternator, which is nearby. When this connection is made, and your key is on, the "HOT" light should be lit. Also, the indicator should light when you are cranking the engine, as a bulb check. If it isn't, check for voltage at the end of the wire, and also check the bulb. This is also a bear to get at, I hope you are limber enough to slither up under the dash! You may be able to remove the bulb by feel, this is the typical PC board mounted bulb holder, so if you unscrew it 1/2 a turn, it should fall out in your hand with the bulb still attached. If the bulb does not light when you are cranking, change the bulb and see if that part of the problem is fixed. If it still doesn't light when you ground the end of the wire at the sender end, perhaps there is a problem with the wire or the connector at either end. If it does light when you ground the end of the wire, and still doesn't light when the engine is overheated (and you are sure of this by virtue of hearing the boiling or whatever), the sender has probably failed. You will have to remove the AC compressor to change it - not a fun job, but it can and should be done without disconnecting any hoses from the compressor - just move it aside far enough to do what you have to do. Of course you know all about this because you have changed the water pump - also not a fun job on these! Now the question is - why is this car suddenly overheating so bad?!? There are so many possible causes for overheating that it is not practical to try to list them all. First thing to check you seem to have eliminated, but I am still suspicious of the thermostat, since it overheats so quickly. While this would not be a good thing to do for any length of time, I'd like to know what if any change you see if you remove the thermostat (I'm thinking maybe there is a mechanical interference problem with it which prevents it opening.) To answer your question, The manual will tell you the proper thermostat, it will call for at least 180, possibly 195, and your car should function just fine with the specified value. Second thing I'd check is to see if the lower hose has the anti-collapse spring installed. We are hearing more and more cases of these springs being left out or even installed in the upper hose, where they do no good at all. If this spring is missing, your lower hose can collapse when you are running at higher RPM from the vacuum created by the water pump, and you'll never know it until the car starves for coolant. You can tell if it's present by squeezing the hose, if it's in there, you'll feel it. Also, take off the main radiator cap and inspect the top of the radiator tubes for particles of crud sitting there. If something has contaminated your cooling system, regardless of the source, there will be pieces of whatever it is sitting there, as these are the smallest passages in the cooling system. If you do see crud in there, it's a good indication that the radiator needs cleaning out (either reverse flush, or better yet, rodding out) and the engine should be reverse flushed also. If worst comes to worst, you will have to pop out the "core" plugs from the side of the block and clean out the water jackets manually. I hope not, this is a messy and time consuming job. Since this car had no prior history of cooling system problems, it is probably unlikely that this will have to be done, but it is the last resort for a badly crudded up engine. Next, I have to wonder, when the heater core blew, if the refill did not completely purge all the air from the cooling system. I don't know how you would tell, except that if the coolant recovery system is functioning correctly, you would "fill" the radiator and put a few inches in the reservoir, then after driving and then cooling down, the level would be dropping in the reservoir to the point where it might be ingesting air instead of refilling with the purged water from the tank. The indication would be that the overflow tank is always near empty when cold, even when you have filled it at least partially before driving the last time. Also, I guess if there is air in the system, you could tell by squeezing the upper hose after the engine cools, if you see bubbles coming from the top tank (cap off) instead of 100% water. Since you haven't noticed any major change in the way the engine runs, we'll not get into all the ignition timing, exhaust blocking and mixture reasons why an engine might overheat - all of those more esoteric reasons show up in driving problems and power loss, or backfiring etc. Also, thank goodness, it means that no damage has been done to the engine by this episode. I'm by no means confident that any of the above are going to lead to a magical cure, but that is all I can think of at the moment. Please let us know how you make out with this.


Follow-up from John:


An easier way to purge air out of the cooling system is to let the engine warm up with the radiator cap removed & as the coolant circulates the air will move into the radiator & bubble out.

From Peter:


I'd suspect the radiator, even though the problem came on so suddenly. I had a 66 Fury wagon (383) that my parents had purchased new and the dealer always serviced it. I can't remember exactly how it began, but it suddenly started to overheat. They took it to the the dealer who told them the block was obstructed and quoted them some horrendous price for pulling the heads and rodding out the block. They took it to a local garage for that work and he didn't find anything wrong. It still over heated so he replaced the thermostat and water pump. Still overheated (violent radiator eruptions and nasty churning noises from the block). They gave up, bought a 76 Fury wagon, and gave the 66 to me: "If you can fix it, you can drive it." I discovered that I could extend my driving range by turning the heater up full blast and opening all the windows. Partial success in hand, I suspected that the radiator was at fault. After all, isn't the heater core just a miniature radiator? I took the radiator to a specialty shop where they offered flow testing. My radiator, which was supposed to flow either 20 or 22 gallons per minute, was flowing only two gpm. Problem solved. For 80 bucks (1978 prices) I got the radiator recored and the car ran great. Check radiator shops in your area for a shop that offers flow testing. It's a pain to pull the radiator but you'll be able to positively eliminate it as the source of the problem. 

Question from Carmine:


 I'm just wondering if anyone else has experienced the following problem, especially in Phoenix (or southwestern US region)...  Normal acceleration during most driving conditions, but fuel starvation during extended WOT (Wide Open Throttle).


Reply from Paul:


From what you have described, the problem sounds to me like an engine heat problem. I think that your cylinder heads are overheating during the full-throttle quarter mile runs at 90 degrees outside temperature. This makes sense because the engine recovers when you let up on the gas, thus the volumetric temperature decreases in the combustion chambers, the pinging stops, and things return to normal. The excess heat is dissipated while you are returning to the starting line, and this problem would not manifest nearly as rapidly at 60 degrees. What I would do is flush the engine with the caustic salts, more than once until all rust and corrosion is out. I would replace the thermostat with a cooler one, perhaps a 160 degree. I would rod out the radiator, and I would inspect the water pump. The water pump should be the heavy duty air-conditioning kind and in good condition. Make sure the impeller has not been worn away by abrasives in the coolant. You did not say which of your cars this was, but assuming it is an RB engine Chrysler, you are running the risk of burning a head gasket by continuing to 1/4 mile in this condition. If I am wrong, and it does indeed turn out to be a gas problem, then just take this for what it is worth! 

Question from David:


I plan to remove the radiator and heater core and send them to the shop.   Then I plan to remove the plugs like you said and clean the cooling system by hand.  At that point what do I do, run water through the system with a water hose?  


Reply from Dick:


Basically, you'll find an incredible accumulation of slop, glop, mud and crud in there, and you have to use anything you can get in there to scoop it all out, or as much as you can get out. 

When you are all done, and thoroughly dirty yourself, flush with water, and, if you have it, an air hose, to blow the stuff out that you couldn't reach. I find a hacksaw blade and an ice pick to be good tools for this. 


I've forgotten what year your car is, but if it has a 440 or a 413, you'll find 3 core plugs on each side of the block. You can get at the passenger side rear plug fairly easily, so pop that one out first. If everything looks quite clean in there, with no more than 1/4 inch of mud on the bottom of the water jacket, I wouldn't bother with the rest of them. The rear plug is always the worst. If there is a significant build up of mud in there, you'd best pop all 6 of them out. 


To get to the rear one on the driver's side, you have to remover the starter. To get the front ones on each side, you'll have to be a contortionist to get at them, because you have to work in very narrow clearance because of the motor mounts. You can make it easy by putting a large block of wood to a jack under the pan to support the engine while you remove the motor mounts, or you can work through the small clearance behind them. I do the latter, out of laziness, but you decide. 


When you begin the process, you'll find two drain plugs in the block, just to the rear of the center core plug. These may be brass, so use a very good fitting 6 point socket on them, to avoid ruining them. You'll probably find nothing comes out when you pull the plug, because the mud is blocking the hole. Push a small screwdriver in the hole and then jump back, because you are going to get a bath in sludge!  

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