Packard Forum Index » Post-War (1946-54)

my 51 is still running too hot, most likely because the engine is still tight after the rebuild. I have a good radiator out of a Patrician - does anyone know if it has any more capacity than the 200 radiator? They look pretty much the same size. The water pump was rebuilt about 1500 miles ago, and the fan is the one with the curved ends. Any other suggestions on improving the cooling? thanks

How hot is "too hot"? Measured how, thermometer or temp gauge?? First you must determine the cause of the "too hot", then a solution. Suggest you refer to the factory service manual or other quality manual of the period instead of re-inventing the wheel.

Have you checked the actual water temp with a thermometer? I use my wifes candy thermometer when she is not watching. If the temp of the water is too hot then I would start the process of elimination. Check water level, pressure cap, thermostat, fan belt tension, ignition timing, and exhaust restriction. A lot of the time the guage is not working properly. I am sure there are more things to check but these will get you started.

I had asked this before without any real response. Do these straight 8's have any problems with trapped air pockets in the cooling system? I know some modern cars have bleeder valves to get all the air out. With the total removal of all fluid, does trapped air ever present a problem? Maybe that is what is going on here? I have to agree with Fred that even if your new rebuild is "tight" it would have been that way from the factory as well. Seems like something else is going on.

Your car may have an overheating issue, and it may not - that remains to be determined. And as we all know there could be many causes which we've discussed a million (OK, not quite that many) times here.

But if there is an overheating problem with a freshly rebuilt engine (edit - which didn't exist prior to the rebuild), it's probably the classic issue. The original engine while it was in use from new, gradually produced less frictional heat as surfaces like rings etc. seated and gradually wore. At the same time the cooling system, most significantly the radiator, likewise gradually lost efficiency but this never revealed itself as the engine was producing less heat at the same time. Now when you rebuild the engine and restore all the additional frictional heat from close-fitting parts, suddenly the cooling system can no longer cope with it. It's a classic; that's why a competent engine rebuilder will also include a radiator recore or cleaning as part of the engine rebuilding process.

As to the original question about radiator interchange, the answer is in the parts book. A quick look shows that a 2401 radiator had use in other models thru 1953.

Looking at the published specs, there does not seem to be an appreciable difference in radiators until 54. Until then all are listed as 19.9 or 20qt capacity and a flow rate of 39.1 gpm. The commercial chassis is slightly higher and there was a separate radiator for AC cars--no specs on that one.

As others have mentioned, if it's not boiling over then getting an accurate temp would be the first step. If this is something that just started after the rebuild, then perhaps the radiator does need attention. If it has always run hot, then perhaps an article in the April 53 Service Counselorhttps://www.packardinfo.com/xoops/html/downloads/SC/SC-VOL27NO4.pdf on some temp gauges reading incorrectly might apply.

Along those lines, would wonder if the temp sender was replaced somewhere along the line or ever. Not having an original spec on the first ones, it is hard to say what it would be unless it is stamped on them. The replacement and later ones in parts manuals thru 56 are listed as 240 degrees. If the temp were verified as reasonable, then at least one vendor sells a sender he lists as applicable 51-6. Might be worth trying if the factory "fix" in the bulletin was never done.

The radiator is boiling over, with the cap whistling until the water cools down. The radiator was cleaned by a local radiator shop while the rebuild was going on. Timing is right on, as is the dwell. First thing I'm doing is going to a 12 psi cap to see if that helps. Then I'm considering getting an overflow bottle, as one of the problems is that it spits out water, then gets too hot as the water level goes down. Has anyone ever used the "water wetter" products? Prior to the rebuild, the car had a tendency to get hot on 100+ days, but as was mentioned above, the new engine has a lot more friction.

Water bottle might help with the losing of coolant & have seen a few installed. Don't think it will solve the original problem though. If the cap is whistling, would assume it is the proper long length. Others have been fooled by trying to use a regular cap that had been sold as correct but couldn't reach the bottom to seal. Any chance of a vacuum leak and it is running lean and hot. How about the exhaust manifold valve stuck closed.

Montana is not very hot at ths time of year I believe. Here in NJ we can run a 51-56 at idle all day long without a cap on it and it does not boil. You have a problem with your engine/cooling system.

As to newly (and correctly) rebuilt engines creating so much friction that they overheat, rememeber that when the car was brand new from the dealer and youdorve it home for the first time , it did not overheat!

Go through dianostic tests as outlined in a good service manual. Once I worked on a Triumph TR3 which had an overheating problem, the impeller was loose on the shaft. Replaced the pump, went for ad rive and it overheated. Checked everythng, dorve me nuts , could not find anythng wrong. Finally removed new water pump, impeller was loose on shaft!!

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Had one thought. Did you replace the radiator cap between the time you pulled the motor and the time you reinstalled? If so is it possible you have the wrong cap. The distance between the top surface of the filler neck on the radiator and the surface where the cap seats inside the filler neck is greater than on most newer radiators. Something like 1 inch. If you just grabbed a 7 pound cap off the shelf at the local auto supply that looked right you may have picked up a cap for a newer radiator that may have a drop of say 3/4 inch vice the 1 inch it should be. Hence the cap would never seat. It would be like running the car with out a cap at all. Something to check. My car had the wrong cap when I got it and would boil over in just a few miles. Installed the correct cap and haven't had a problem in years.

The other thing is that you will always loose some water overboard if you top the water level off. As the water gets hot it expands and has to go somewhere. That somewhere is out the overflow tube and onto the ground. When it boils over and you let it sit and hence stop venting water and you restart it does it start to boil over again as it warms up? Where is the temp gauge sitting when it boils over.

If you check the water level after it cools down and you can check it without loosing a lot more water is the level say 1 to 1 1/2 inches below the top of the radiator or is it well below that level with the tops of the tubes showing with no water above them? If the level is only say 1 inch down I would run the car again and see if it just warms up and boils over again or will it then run without loosing any more water.