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Classic/Antique Car Repair/68 xr7 cougar over heating


QUESTION: Im not sure what to try anymore. Car over heats at idle, it's a 302 with a Holley 4 barrel Carb. After rebuild motor was running hot, not sure if it's actually overheating. Radiator cap was. Ad and I replaced it but it still over heats. Also replaced thermostats recently and water pump was replaced when motor was rebuilt about 1500 miles ago. Also bought the right radiator since it bad a smaller one before. I have Also changed the ignition coil because I read some people said a bad one COULD cause overheating, didn't fixit but fixed some stuff. The smell of ogas is really strong, would bad Carb adjustment cause motor to run hot. Also my automatic transmission is slipping, could that be a cause. Why is the smell of gas so strong, I understand exhaust but gas? Sorry so many questions but normally I just search forums not ask questions. So I changed water pump, thermostat, radiator (used), radiator cap, ignition coil (long shot). Only other things I could think of are timing and advance vacuum but bow do I check those and could it be the cause. Before it gets to hot it seems to drive OK other than transmission. Once it gets warm ttransmission starts slippimg more and car trembles once in a while but no smoke, steam nothing, just a stream of water under my car about 15 feet long. Could it just be the tachometer, how do I check it or check what temperature is actually at, I Also changed temperature sending unit. What about a blown bead gasket, think I read that so.where too. Sorry so long but hopefully you have all the information you may need, any advice would help for I'm just trying anything g that might help now. Oh it was factory ac but was taken out

ANSWER: Hello James,

It sounds like you have a number of issues going on. I'll try to get you back on the right track.

First of all, rebuilt engines, if they have been overbored due to wear, usually will run hotter than the original. Overheating at idle is indicative of either a blockage or excessive air in the cooling system. Check hoses and flow through the radiator, the coolant should be flowing like a small stream through the upper radiator tank at idle. Beware that used radiator...did you have the internals boiled out and cleaned? If not, do so. If still no success, start tracing backwards though radiator, hoses, thermostat (should be 180 degree) and even your new radiator cap. Don't assume a part is good just because it's new, particularly if you got it at a Big Box auto parts store. Always buy OEM equivalent parts or from NAPA stores. This does not infer that there are not other reputable sources, but you're most likely to get a better part from these sources even though you might pay more.

A couple more tips, check your timing: retarded timing can make your engine run hotter. You can get the procedure on how to do this on line. Same for checking distributor weights and vacuum advance also.  And, if none of these things help, consider mounting an electric auxiliary fan BEHIND the radiator (so it draws air through the radiator) may be in order. Finally, does your car have a fan shroud? I believe some air conditioned cars did. Fan shrouds help the fan cool better. Find out where that stream of coolant is coming from, radiator or hose or?

There are many more cooling checks, such as checking to see if your heater (has a small radiator) is plugged, but this should get you started on the basics. Changing the ignition coil
falls in my possible but not likely category. Check the preceding basic items first, then go into less common causes like the coil.

Strong gas smell is serious and should be priority #1 due to safety, not to mention loss of the car. In the same systematic manner as the cooling system, start at the fuel tank, checking for leaks, seepage etc.. Check all fittings for tightness, especially carb to manifold nuts. Check carb for seepage, correct internal specs., including float level and correct automatic choke operation. Write me again if this doesn't work and I can give you more suggestions.

Finally, your trans. slippage problem is probably unrelated to the above. Take it a reputable transmission shop for diagnosis. Meanwhile, with vehicle warm, and running, check your transmission dip stick. Is the transmission full, is the fluid bright red or yellowish? and does the fluid smell burned? These simple tests can confirm whether you simply need a minor servicing and adjustment or major service.

Finally, I don't understand your tachometer question as tach's measure RPM and not temperature.

Good luck. I love these early Cougars too and particularly XR7. I've thrown a lot at you but if you check methodically, you'll find the problem and it may be more minor than you think! And even if you don't initially find the fault, at least you'll know what it ISN'T and that's valuable in and of itself in vehicle diagnostics.

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QUESTION: Car is in shop for transmission rebuild, I will let you know once I get it back. Had motor rebuilt and transmission has never been right. Now I will be able to trouble shoot wwithout that concern, sometimes it felt I was over revving it but barely moving. So gas issue first then heating, I'm going to buy a new water pump and go from there seeing as my thermostat had some gunk on it, water pump might as well. Water is flowing through radiator but not a stream, just moving so water pump and flush, then radiator. Is it possible I might have a blown head gasket causing gas smell in oil or possibly water in oil. Get my car back Saturday, Sunday I will be under the Hood, or Saturday night thing considering.

Hello James,

Thanks for the kind words. They're appreciated!

Reading through your response, a couple of thoughts come to mind:

1) Transmission rebuild was a good idea. No need for my tests now, but just in case. See below.

2) You might need a new water pump, but it should have been replaced during the rebuild. SOP: Standard Operating Procedure. Unless it is leaking or the shaft is wobbling, I'd suggest looking elsewhere. See below.

3) The gunk you found on the thermostat indicates that you still have a major amount of debris in the cooling system. Yes, I know it's rebuilt and the block should have been "boiled out" (reverse flushed with a caustic chemicals)but remember what I said about parts being new but aren't any good? Well, same goes for repair procedures. It could be your untested radiators (remember  core?) adding the gunk to the system or debris left in the block but what you need is a complete, reverse flush on your cooling system. It could do wonders for your cooling problem. Instructions on how to do it are on the Web or take it back to the folks who rebuilt the engine. If they're reputable, they should offer to do the job for you, no charge.  

4)You are correct that foreign chemicals in the coolant could signal a blown head gasket. A gas smell in the coolant could indicate this but it could more likely be a fuel leak in the same area on the engine. Best place to initially check bad head gasket is in the oil. If oil is increasing in volume, this could be due to coolant leaking as oil floats. If your oil has turned a dirty brown and seems to have lost some viscosity (thickness)is a classic sign of a blown head gasket. New gaskets should have been part of the rebuild so it should be a warranty issue although I'd be wary bringing the car back to a repair shop when this is the second strike against a workmanlike job.

Good luck on that Cougar!


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Robert Russell


Mechanical, Body, Historical, MOPAR, GM, Ford, Packard, 1930-1975


Former Chrysler Tech., Project Manager for Antique and Classic Car Dealership. Owner/Driver of Classic Cars Since 1972

AACA, North GA Mopar Club, Packards International, W.P. Chrysler Club

High School Auto Shop plus Adult Night School

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California Car Company, Roswell, GA

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