Got a problem, need help from more learned folks. Just got through rebuilding my 390GT out of my 67 Cougar. It's been bored .030 over, balanced, new valve train, heads have been port matched and polished, Canton windage tray, new Edelbrock Performer 390 intake. Started it on a break-in stand. Noticed the left bank getting hotter than the right bank, can't even stand to touch the valve cover for very long, even the spark plug boots are too hot to handle. Pulled out the old Inferred Thermometer, #1 was 750F, #2 is about the same, #3 is 800F while #4 - 8 are running about 600F to 650F. Intake vacuum is running between 14-17 and reving to about 20 in/Hg. Pulled the valve cover while running and sprayed a little carb cleaner around the Intake Interface to look for leaks and got no engine rev. Could a backwards head gasket cause this kind of problem? Everyone I've talked to has never heard of just three cylinders running hot like this. I've got 120 PSI on all the cylinders. What's up. I've checked the head gaskets and they're installed correctly. Can anyone please help.

 

Please excuse my ignorance on running engines on a break-in stand, but where exactly are you measuring these temperatures? The engine block, as far as I know, should stay below 250 degrees Farhrenheit. The water boils at 212, and the coolant should be good for 20-30 degrees more, but not 650 ... Are you running it on the stand without cooling?

Leaving this issue aside, and assuming your IR thermometer is messed up and you do have cooling in place, I would suspect one of the cooling channels in the block is plugged, which makes the local cylinders run hotter. It could also be an issue with improper lubrication (not likely though), or higher friction in those cylinders because of bad rings ... I'm shooting in the dark here, but for the lack of better ideas ...

HTH ... good luck!

 

I wouldnt use an infrared thermometer. Thermocouples are the way to go for accurate measurments of temperature. Also, those temps sound like what your exhaust temps should be at idle @ the catalysts or manifolds. And if you were actually reading the exhaust temps somehow, a difference in temps from either bank could mean a fuel mixture imbalance or ignition timing issues or both. Cougar_Fan is right, your engine should never exceed 250 degrees. Your engine should actually be somewhere around 180-200 deg.

 

Just out of curiosity, when you stated the head gasket was installed correctly , did you remove the head and actually check the coolant holes to insure none could have been blocked. That may be your next course if you can't come up with the cause before pulling the head.

 

I cut my teeth on those old cows, and I've seen this before. I totally agree w/Hanky (of course). These head gaskets are a total Pain in the .... to get on right; and the holes for the water passages are easier then anything to get on wrong. Been there before. I feel your pain.
I really loved those old cougars; they were so pretty!

 

Hey guys, thanks for your response. I haven't checked in a while. I'm measuring the exhaust at the header tube as it exits the head. yes I am running coolant, actually, I have the radiator on a stand in front of the engine and the fan is installed on the water pump. Engine temp is about 185 to 190F. I have a 180 degree thermostat installed. Yes i did pull the head gasket and it was installed correctly the main hole was in the back and no other holes where covered. The block has been vatted and blown clean, I checked the water flow myself. I ran a bore scope through the intake on each tunnel all the way to the intake valves looking for blockage and found none. I even ran it up through he header tubes and didn't find anything that could be causing a back pressure problem. I have the original style 600 CFM Holley that I rebuilt on it and have it idling pretty well, it's not missing and revs very well. It just kills me to go to all this, doing everything as right as possible to have this screwing with me. Like I said, it's been bored 0.30" over, new pistons, rings, balanced, miked, port matched, Canton windage tray, Mellings high volume oil pump, I did the oil mods to the engine, new valves, Comp springs, cam (Comp High Energy), lifters (Comp), hardened oil pump shaft (ARP), ARP Main bolts, and a Accel Ignition points eliminator. I mean, I'm not just talking about the exhaust temp being high, the whole right hand valve cover gets hotter than the left one. I don't know guys, could it be that I just need to replace the 600 CFM and go with a 670 CFM Street Avenger? The only thing I haven't tried is to put the old cast iron intake back on and see if I still have the problem. If it solves it, it could be the edelbrock. I don't know.