Repair Information On Your Imperial's Overflow Canister


Imperial Home Page -> Repair -> Cooling System -> Radiator -> Overflow Canister

Question from Donald:

I would like to put overflow reservoirs on my 1955 and 1967 but have not found a source for these, NAPA does not carry these.


From Chris:

Ask at the counter... maybe they were out of stock. I found a new one for my car at my local NAPA, and it looks just like the one that's been on the car for 20 years. I've also seen them at Pep Boys and other auto stores.

From John:

You used to able to find them in places like Pep Boys or Auto Zone ETC. But since all cars have been equipped with these for the past 20 years or so, they are a lot harder to find. You would surely have no trouble getting a used one.

From Bill:

Advanced Auto Parts used to carry a universal one, might try them.

From Paul:

The earlier cars did not have overflow kits. At that time, the top tank on the radiator was called the "expansion tank" and was NOT supposed to be filled to the top when cold. If it is working correctly, the coolant level is correct, and the right pressure car is used, the top tank will not overflow.

Obviously, as our cars get old, they may tend to run hotter, and a coolant recovery system isn't a bad idea anyway, but if everything is as it should be, it is not necessary. An ongoing overflow problem would be an indication that something else is wrong.

From Phil:

One thing I have on most of my older Mopar drivers is a homemade recover system. All it is, is a antifreeze bottle wired up in an out of the way place, and a coolant recovery cap from the local parts store and enough black rubber line to reach from the vent on the filler neck down into the botte. Leave a little coolant in the jug to cover the end of the hose. Just try to get the correct rated pressure cap cause some of the late model caps have much higher pressures than an older car would ever use. Not pretty, I know, but easily removeable for shows, just let the car cool,
take off the bottle, replace the cap with a correct one, and you're done! PS: as always, be very very careful uncapping any hot radiator.

Question from Bill (1959):

I was wondering if anyone had tried to put a coolant overflow canister on an older Imperial. Today was a pretty hot day here in So. Cal., and I drove my '59 to work. I had a few associates tell me my car was leaking coolant, but I told them the older cars just have a tube running to the street, which is why you had to check the water every time you gassed up. Today I had quite a bit boiling out in a river through the parking lot, since I just topped off the radiator the last time I drove it. After seeing how much went out, I will have to check it for coolant before I drive to work tomorrow, and when we get some of the really hot 100 degree days in summer, I'm afraid I will have to carry around a jug of coolant in the trunk. It would be easy to put in an overflow canister, and there is plenty of room. I was just wondering if it would work?


From Wayne:

One thing to remember, is that the radiator should not be filled to the top. Add just enough water to cover the fins. The top of the radiator is for expansion

From T.L.:

An overflow should work, in theory. As your coolant heats up it expands and will find any escape route, like your drain tube to the street. If that drain tube went into a reservoir it would keep all the environmentalists happy first, and second as it cools it should siphon the overflow back into the radiator. Try maintaining the level of your coolant about an inch or two from the bottom of the radiator fill neck when the motor is cold to minimize overflow. Also check to see what the recommended pressure rating of your radiator cap is for your specific motor. The purpose of the radiator cap is to control the boiling point of the coolant/water mix by keeping it under pressure. Hence "NEVER OPEN WHEN HOT!" If this condition persists you may want to replace your thermostat. If it is defective, i.e. stuck open or closed, the circulation and cooling effect through the motor will be greatly compromised.

From Rodger:

"I had quite a bit boiling out in a river through the parking lot" suggests some other problems with the cooling system. This is a good time of year to service your cooling system, new thermostat, reverse flush, maybe take out some "freeze" plugs and clean the gunk out of your water jackets.

From Bob:

A prior owner had put an overflow bottle on my '66, in front of the radiator (PLENTY of room) on the driver's side. Seems like an easy thing to do and easily reversed if you want originality later. I believe a different radiator cap is needed.

From Pete:

1) You should not be filling up the radiator on your car. Check the owners manual. I think you'll find that the coolant level should be about 1.5" below the filler cap neck. This airspace is there to allow coolant expansion and prevent coolant overflow. Filling the system up right to the bottom of the filler cap neck WILL cause coolant to leak out the overflow when the engine heats up following shut down. 2) Adding a coolant overflow tank to any coolant system is a great idea. Not only will it prevent spewing of coolant onto the pavement, it will reduce corrosion in the cooling system. This is because the system can be totally filled on a recovery tank-equipped vehicle, while "ordinary" systems do contain air (for the reason given in 1). The air contains oxygen, which allows oxidation/corrosion. No air -- greatly reduced oxidation/corrosion. Most auto parts stores will carry a universal recovery tank setup.

If you do add a recovery tank, be sure to install a recovery tank compatible radiator cap, too. Or the system won't work. And I'd use a low pressure cap like 7psi or so. Modern systems routinely run at 16 psi or so but I'd rather loose some coolant via overflow than have my heater core blow out and drench the carpet!

From Dave:

Bill, I put one on my '65 Crown. On the hottest day here in Chicago last summer(90 degrees) mine didn't boil over or run hot. I mounted mine on the driver side right next to the radiator. I has helped, something I can't say for the bottle a buddy of mine put on his 69 Road Runner !!!

From Phil:

I have a non original one installed on my '68 coupe. It's a driver, so I'm not worried that much about originality at this stage. All you need is the coolant recovery cap, and something to use as a reservoir. Just be sure to check the rubber line used has no leaks, or the system won't be able to maintain vacuum. When that happens, the reservoir just becomes a catch can, because any vacuum leaks will prevent the system from drawing the coolant back in. Also, and this is the most important part, be SURE that your coolant recovery cap isn't too high of a pressure for your vintage Imperial. I've made this mistake before myself, and it's cost me split radiator tank seams and leaking freeze plugs before. You can get recovery caps in about any pressure rating, but most of the ones on the shelf are for modern cars, which are ran at a much higher pressure. Your parts store should be able to order you a lower pressure recovery cap to match the one on your Imperial, if they don't have one on the shelf.

From Charlie:

I'm not positive here, but I think you would need to change the radiator cap. With an overflow bottle the cap must seal on expansion to the desired setting and then allow the coolant to siphon back when cooling. I don't think that pre-overflow bag/bottle caps had this feature. They just sealed tight.

You should fill the radiator full, the bottle is the expansion area.

From John:

I couple of things to check are, don't fill it too full. It should an inch or so from the top of the neck. If you keep filling it to the top, it will keep overflowing. Make sure the radiator cap is good & of the correct lbs. A non A/C car should have an 8lb cap & an A/C car should have a 14lb cap.

From Steve:

Pete gave some good advice and sums up my experience with overflow bottles on Imps.

However, if you are experiencing continual overflow and hot running, you may have a hidden condition the overflow tank won't be able to control:

Clogged water passages in the Engine Block.

My '64 developed this condition and a flush with the block drains open didn't fix it. Probably nothing short of pulling the freeze plugs and scraping and dredging the sediment out will get rid of this situation. My engine rebuilder told me about this development after he fixed it by boiling the block (of course, a more drastic approach). Consult the FSM.

Pete's horsepower versus paycheck analogy was beautiful. Again, here I'd like to add that if you're retired U.S. Military the "drag" goes a little further.

Question from Curt (1974):

The coolant recovery tank on my '74 440 takes in fluid but doesn't return it to the radiator, what could be the problem?


From Dick:

Your radiator cap is the wrong type, or else the seal is not working. Try a new radiator cap, and be sure you get one for a coolant recovery system. Inspect the sealing surface at the top of the radiator neck, it must be smooth and clean or the vacuum won't pull the coolant back into the radiator from the recovery system.

From Roy:

You probably have the wrong radiator cap. In order for a recovery tank to work, the cap must seal in both the bottom of the neck, like all radiator caps and also at the top edge of the neck above the recovery tube. This is so that the vacuum created once the engine cools down after it is shut off, can suck the excess coolant back into the system.

From Charlie:

You might also check that the tube and fittings from the radiator to bottle are in good shape. No cracking, loose connections, etc. If cracked it could suck air instead of water.

This page last updated May 28, 2004.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club