VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Advice Sought on 40 Groaning Noise

Most strange. Car runs fine but when the engine is turned off after a ride, there is a low groaning noise that lasts about 5 seconds then stops. Sounds to me like it comes from the radiator. Fluid level is full (an inch or so under radiator neck), a 7 lb radiator cap is in use, and vehicle is fitted with an overflow tank. Does not appear to effect engine operation in any way at the moment and noise is new within last month or so. Thoughts/advice? Thanks, Bob

I don't believe pressurized radiator caps were in use for a number of years yet. Not sure when Chevy started pressurizing the cooling system. Don't know your system but that's a place to look.

Tiny, you are correct. Pressure cap was not in use for the 40. I'm using the light pressure cap to help avoid overheating. I have made no change to the radiator cap or thermostat and operated without a "groan" until recently. Have not had overheating problems in the last year, or longer. Certainly easy to run a non-pressure cap just to see if any change results but it seems unlikely given the recent history and thanks for the suggestion.

The groan can be from air or steam causing a vibration when flowing through a small passage or restriction. I expect it will come and go depending on the ambient temperature and flow rates. Sorta like your growling "stomach".

The 1940 filler neck is not designed for a pressure cap.

My 37 would do that after running it hard but I had a 57 235 in it with a shortened water pump with the 216 size pulley which I think spun the pump too fast,installed the adapter with a 54 pump and has not done it again.

Chipper, well....I have a lot of experience with a growing stomach so I'll look for change under different heat conditions....all the times I have heard it, the engine was well warm and during hot weather days hear in Virginia. I'll give it run some cooler evening and look for any change.

Gene, my radiator is a replacement as the original was discarded sometime back. The replacement radiator neck does have shelf in the neck that allows the cap to snug up against. That said, are you feeling that the 7 lb cap could be part of the problem as Tiny was thinking?

Jeff, interesting and perhaps your set up was producing a vibration causing some noise as Chipper described. I had thought I might have water pump issues, but mine is a relatively new pump, the vehicle doesn't overheat, although it has always run on the hot side in hot weather, mostly when idling for a long period....raising the rpm for a minute or so, brings the temp down a bit, so at this point the pump seems to be functioning normally.

Really appreciate everybody's thoughts/ideas, Bob

Knowing it's a replacement radiator makes a difference. I was assuming you put a 7lb cap on a radiator not made to hold pressure. Complete information provides better answers. Hope you get an answer.

If the overheating is getting worse each year it indicates rust from the block is slowly plugging up the tubes in the radiator.

Agreed, complete information is always better....sorry not to have mentioned the replacement earlier. The good news is the car isn't overheating....just the phantom groan....but rust from the block certainly could be a factor causing hot running and perhaps, I guess, resulting in the groan. I'll see what more I can learn.

I'm thinking that your "groaning" could be caused by your pressure cap by-passing air as your water temp rises immediately after shut-down as the 216 and 235's tend to do. Try driving it with the cap loose and see what it does since you say its not overheating now.

I agree that if your radiator is correctly configured for a pressure cap (that is a big assumption) the groan is probably the cap “relieving” itself.

You could try a different cap. Or this is a simpler test. Have a second person turn the engine off while you stand out by the radiator cap and listen there.

As a reference my ”˜37 has a 160 thermostat. It runs at 170 which is normal because the rear of the block is hotter than the front. When I sit at a light on a 85-90 degree day it will go up to 180, maybe 185. It immediately drops back to 170 when I start driving. It drops some if I use the hand throttle to spend up the engine slightly while sitting at the light. That makes sense because the fan is moving more air.

Crud buildup in the block, head, and radiator are the reason these engines overheat.

Mike, Rusty, thanks for the comments and I'll experiment with all the ideas suggested, much appreciated, Bob