Overheating 1992 Mercury Capri (Australian-Made)


My Capri has a severe overheating problem. The conditions needed to produce it are as follows:

Speed under 40 mph

At least 20 minutes of run time (driving, not idling)

Heavy bumper to bumper traffic -or-

Driving up a steep hill

Before it overheats: the problem starts as there will be a rattling noise that sounds like metal scraping metal coming from under the hood somewhere. This happens between 2500 and 3000 RPM on the tach. Once the problem becomes more pronounced, usually in stop-and-go traffic or slowing down and accelerating, the car starts to drag (retarded acceleration). If the problem is allowed to continue, such as when you are in the mountains, it will refuse to shift up into a higher gear. Indeed, it won’t even speed up no matter how much gas you give it. At this point the car slows from 30 to 25 … then 25 to 23 … and eventually it won’t even get out of first and it’s moving at 5 mph. I don’t know how I got the car through the Blue Ridge Parkway like that, but I did.

I have already:

Replaced the thermostat, radiator, upper radiator hose, water pump, and the engine has new spark plugs.

The problem continues. I’ve spend a good deal of money on this car and I want to keep it. But nothing I have had done to it so far has even gotten to the root of the problem.

I’m considering asking my mechanic to do a compression check on it to see if the problem isn’t in the engine, but I’m thinking it may be a transmission problem all along. Could someone have the answer to that?


I hate to suggest it, but it sounds like the main bearings are binding up. If my hunch is right, I’m surprized they haven seized by now.

A plugged exhaust system comes to mind also, but this sounds more severe.

I’m a bit confused, however, because you didn’t describe the overheating symptoms. Can you clarify?


The symptoms are retarded acceleration and … isn’t overheating a symptom in itself?


Well, how do you know? Is it merely based on the temp gauge or light, or is there steam coming from under the hood?


If that rattling sounds like a marble rolling around in a coffee can, then that could be detonation from overheating. The dragging sensation could be pistons trying to seize in the cylinder bores. An overheating engine does affect the transmission since the trans fluid is cooled by the radiator trans fluid cooler.

Just wild guessing here, but I’m leaning towards a clogged converter. Depending on the severity, power loss can be gradual and overheating can be severe - even enough to roast an engine.

In a shop setting, the first thing I would do is a compression test and connect a vacuum gauge. The latter will give an indication if the converter is clogged. Depending on the results of the compression test the converter may be irrelevant at that point.

I’m also assuming here that no one has been dinking around with the distributor. Timing that is too advanced or retarded can cause some big, serious problems.


Is the fan running when its really hot? I don’t know this car at all, but so many cars have electric fans now. If the fan motor or the relay or sensor is broken and the fan doesn’t run, you could have these problems.


I don’t know if anyone’s done ANYTHING to the distributor, but what would that cause besides what I’ve described?

I think it is the convertor …


Having the ignition timing too far advanced will cause rattling, overheating, and engine damage over time.
Having the ignition timing too retarded will cause loss of power, overheating, and due to essentially trying to force the engine to run richer, could lead to a clogged converter over time.

Easiest thing to do is connect a vacuum gauge and see what’s going on followed by a compression test. Chronic overheating will kill cylinder walls by glazing them and also kill piston rings by either seizing them in the piston lands or removing their spring tension and turning them into the mechanical equivalent of wet noodles.

A clogged converter can definitely cause all of this. We had a guy pull up to the shop one time complaining that his car was barely moving. Raised the hood (Cadillac) and both exhaust manifolds were glowing red. It was hot enough that the paint on the hood was even starting to bubble and it was all caused by a clogged cat.
Needless to say, the engine was scrap iron.


Are there any possibilities beyond:
clogged catalytic convertor
seizing engine parts (main bearings/crankshaft)
transmission problems?