[tschwengler]

I need some expert advice. My 72 Challenger 340 is overheating after I rebuilt her. The machine shop said the heads and block were not cracked. I have a new radiator, (to original specs), water pump, thermostat, hoses, and she still gets hot, real hot. Could punching out the engine to 40 over cause the overheating? Please advise.

[dave-r]

I am having the same problem myself!

I have hopefully tracked my problem down to a blowing head gasket. If the water is going around and getting the same cooling it had before and the only thing changed is the re-bore it has to be a head gasket or a crack in the head or block. Was the cylinder wall thickness checked before the re-bore?

Try taking the water thermostat out and see if it still gets hot (although it will take longer to get up to temp) just to make sure it is not faulty or upside down or anything.

[Yarek]

If you have crack in cylinder head or burned gasket you can see bubbles in radiator.
Took out the radiator cap (of course not on hot engine) and look on "water". If you see big bubbles and you can smell the exhaust gasses from radiator it means that something is wrong.
It also causes overheating of the engine.
I had similar problem in my 440.

Or... do you have viscotic fan or "solid"?.
If viscotic fan is week the air flow through radiator is not sufficient and engine will be overheated also.

Good luck
Jarek

[tschwengler]

I thought about a blown head gasket, the engine has only about 7 hours running time since the rebuild. What is catching my attention is, the new paint on the intake manifold near the center on both sides has burned up. Turned to ash almost. I took off the fan clutch and put on a solid fan and also put a trans cooler on. She still will not run without getting hot. Right now I have the timing chain cover off checking the timing chain alignment. I can't time the engine below 9 or 10 degrees advanced without stalling. I will remove the thermostat and also look for bubbles in the radiator soon as I get her back together. Thank you!

[Henry]

Was it running okay when first rebuilt?

Have you checked obvious stuff like oil, coolant, torqued up nuts & bolts, etc?

[tschwengler]

She fired right up when I got her together. She just got hot quick and like I said the timing is set pretty high to keep her running. Oil and coolant is fine. All bolts torqued to specs.

[Henry]

Clues to head gasket probs are oil in the coolant or vice versa.

Another remote possibilty is an air lock caused by a blockage in the engine stopping the coolant getting around but this is a remote one.

[Jack T]

My father ran into similar mysterious overheating after he had a 440 rebuilt and blueprinted. The shop that did the work finally determined that the head gaskets were for a later year 440 and that some of the water passages had been closed off to make the later year engine run hotter and therefore "cleaner" in the eyes of the smog laws. After they bought new gaskets, made sure all the openings were where they should be and assembled the engine once again, the overheating problem was cured. You might want to check this possibility.

[tschwengler]

I drained the oil, no water in it, drained the water, no oil in it. The gasket water openings sounds like it could be the problem. The engine is heating up on both sides not just one like a blown head gasket. Is there any way to determine which passages should be open? I know some of the middle passages in the gaskets were some pretty small holes compared to the holes in the block and heads. And like I said the heat seems to be in the middle of the heads where the paint has burned off the manifold on both sides.

[Jack T]

I'd make stencils from rubbings of the faces of the block, cut them out and compare them to the faces of the heads to see what the opening limits are. Also, you could take the 1972 gaskets and check them against ones from 1970 if you have access to them. I am only speaking from my father's experience and what he told me about it, so I am almost as much in the dark as you are.

[dave-r]

Paint burned off the manifold? Which manifold? The intake?

Just a long shot here but check that the exhaust cross over butterfly thingy in the passenger side exhaust pipe has not jammed closed.

[alex bracket master]

The paint always burns of the intake unless you fit blanks to the crossover.

Have you driven the car for seven hours, or had it sitting around? one thing you guys may be overlooking is that the engine may have been assembled "tight", this will cause the engine to run hot till it all breaks in. The holes in the gaskets are smaller than in the castings, check the gaskets are correct for the year. The heads I think Jack is referring to are the "motorhome" heads that had an extra set of holes around the spark plugs to help cool the motor because of it's position and the extra weight it had to pull. By the way these are real good heads if you can find them! if you still cant see anything definate, an easy way to check for head blow is get a freindly shop to put a gas test pipe just above the water in the rad, so it sniffs the steam, if there are any exhaust fumes present, they will show on the machine!

[tschwengler]

Yes, the paint has burned off the intake manifold right in the middle only. Both sides of the carb. The car has dual exhaust without the crossover butterfly. The car has been run for aproximately 7 hours since I rebuilt the engine. The holes I referred to being smaller were in the middle area of the gasket and they were not as big as a pencil, were the holes in the castings were at least nickel size.

[Henry]

How long from initial fire up did it start to overheat?

[tschwengler]

The engine temp raised up right away. The temp here was 105 so it did not take long for the engine to heat up. After around 45 minutes the engine temp was pushing 200. I have a 180 termostat installed. When the engine reached around 220 I sprayed the radiator with water cooled it down and shut her off. I could here boiling at the thermostat.

[Henry]

Gotcha.
So it points to either incorrect gasket or tightness as mentioned above rather than something going pear shaped after it had been run.

[Douglas]

Last year I rebuilt my 340. The man at the speed shop said to let the engine run 20 min on start up to seat the new cam with the lifters even if I had to spray the radiator to keep it cool. It got hot and quick. The wrong paint on the exhaust manifolds finally caught fire and burned a few wires. I don't think I made 20 min. Problems corrected it never ran that hot the next time. Turned out to be a great engine. Maybe your engine is just a little tight and all will be well on the road.

[Christer]

A few suggestions: You have torqued all bolts to specs. That´s good. But have you cleaned the threads (with a thread cutting tap) before you torqued the bolts? That is a good thing to do before reinstalling the heads.
Have you ever checked if your torque wrench shows the correct value?
Another thing: How is the fuel/air mixture? If it is too lean the engine is getting hot.

[alex]

It may be a good idea to check the stat, get an old one and chop the spring, pull the centre out, and fit the case into the system and run it up. Do not run without a stat case in there or you will get localised overheating due to the speed the water will flow through the heads. It may be an idea to run this way for a couple of hundred miles if it works until the engine frees up.

[Henry]

If you have a decent thermometer you can check the stat in a container of hot water by heating it until it opens.

[tschwengler]

Okay, I have several things to check and look at. I will not have a chance until the weekend, but, I thank all of you, Henry, Alex, Dave, Christer, Jarek, Jack, Douglas, and Alex Bracket Master for your comments. I knew Mopar owners would have answers and ideas. I will reply after I have had a chance to check out a few things. Thanks again all!!

[fjl]

I had the same problem with a stock 71 340 128K and TQ carb. long and short of it was timing needs to be 2.5 to 5.0 degrees BTDC, Carb needs to be adjusted rich. the emissions holley 650 i was running was too lean. threw away the limiter plugs and max'd the rich settings. Finally i am running 0 degree freezing antifreeze 80/20 water to antifreeze mix with a jar of water wetter in the radiator runs at 180 all day long including stop and go freeway commuting traffic. All the advice you have received is right on. been there done that forgot the basics and lost a summer of cruisin.