1940 Chevrolet Overheats Under Load

Is this a stock motor? Did you replace the heads. Did you put the right head gaskets on it. If you have done any of these things it will over heat if you did not match up the steam holes in between each cylinder. Heads other than 400 stock heads do not even have the steam holes and you have to drill them yourself or have good auto-machine shop do it. If you put the wrong head gaskets on it they are probably blocking the holes. If this is not the case go buy another $30 water pump and see what happens. Flushed your radiator lately? Pull it out of the vehicle and flush it. You will be amazed at what comes out. Air conditioning condensor in front of the radiator? Pull out the radiator and clean that rats nest of leaves and stuff out between them. What kind of fan are you running? Have you ever replaced the clutch fan? I think they are a piece of garbage. A fan looking for a radiator to destroy. But the one on my truck has gone 190,000 miles. Knock on wood.

You don't mention if there is anti freeze in the oil or oil in the anti freeze. This is a tell tail sign that the headgasket is blown along with white smoke out the exhaust pipe. If you don't have any of the above mentioned then I would suspect there is a problem with the coolant system. Check the simple things first before moving on to more complex items. First is the coolant level correct. Next is the fan belt tight and not slipping. Check the radiator and block for cloggs. ( Inside and the outside) Make sure the fins are clear of debris. Check the clutch fan ( if equipped) is working properly. You can do this the following way. With the truck cold attempt to spin the fan. The fan should spin a few turns freely. After the truck has reach operating temp shut the vehicle and attempt to spin the fan. There should be resistance when turning it and not spin freely. Next and finally you can check the water pump without removing it. With the cap off the radiator (do this with the engine cold) start the truck and wait for the thermostat to open. Once it opens look into the neck of the radiator, You should have the coolant flowing freely across the top. Also with the vehicle at operating temp squeeze the upper radiator hose for a few seconds and then release it .If the water pump is working you should notice a surge in presure in the system.
Hope this helps Backyardmechanic :roll:

To answer as many questions as I can remember, I did replace the hoses and which dropped about a gallon and a half out of the system and I replaced that. The oil is perfect, full all the time and no signs of antifreeze or over full readings. The motor is mildly built with a cam and a weiand intake, but it ran great for the 2,000 miles before this occured. The smoke out of the exhaust is shear condesation dissipating from the cold. She has practically no exhaust restriction so it spews water out, but I do not smell any antifreeze in it. The white cloud seems to go away pretty fast and if the gasket was bad, I was told the cloud would be huge and I'd know. I have not replaced any heads or anything except for the hoses and thermostat and cap. The radiator is clean and nothing is clogged up front. There is no AC condensor since she does not have air. I need to get it pressure checked but cannot get the truck to the shop since it overheats 1/4 mile down the road. I guess I could make it there just giving her time to cool off before she does burst the head gasket, but I am just looking into any possible recommendations before I have to spend too much money like I already have from other problems I have had with her. I will run the truck with the cap off, but I have done this and she seems to overflow a bit which could mean air in the system or a blown gasket. Should i just let it try to get any air out or should it not come gushing out when I have the cap off??? Thanks again for your help. I will look into all your advice so far.

I also have checked the fan and it runs a little resistant once the truck is shut off from running and it is a clutch fan. I forgot to mention these questions but I have checked into them as well. I also did have a small accident with a construction cone on my way back up to State College where the guy in front of me hit a cone and it flew into oncoming traffic and he hit it back to my side of the road and I took it to the driver's side under the engine and it snapped my belt so my battery died and all that good crap. I replaced it once I got towed to the nearest shop and put it on but it seems to have a little slack in it since I checked it the other day when I was putting the lower hose on. Simultaneously, when I hit the cone, my rockers cracked my aluminum valve covers since the previous owner put the passenger side on 180 degrees the wrong way and chevy's have an offset so it ate through and I was gushing oil everywhere and thats when I pulled over and my battery was dieing due to the belt snapping and keeping the alt. from keeping me charged up. It was the day after I made it home 11 hours later (2.5 hour trup) from the valve cover and belt problems that I had my first overheat. I had to add a gallon of coolant and since then have had this problem. I cannot imagine how these can be related. Also, the catalytic converters glow and started to melt my new glass pack mufflers especially the passenger side (the side that had a broken spark plug and the valve cover problems) This all happens the day after my nightmare trip back to State College. If you have any advice about how one of these can lead to the other let me know! Thanks a lot.

One blown head gasket and the other was cracked and also had valve damage and a cracked head. Got the new head for 50 bucks and had both heads drilled out 30 thousandths over so I did not have to get the new guides tapped out. Oversized valve stems and a boil and shave should do it. There was stop leak in there too so I think somone before me knew about it! That bonehead. Got the gaskets and seals and valve rollers and it should be done soon (second week in January)

Thanks for all the help

it sounds like you will have it fixed good job.