Have a 92 with ford motorsport 3 row rad. Boiled over last year in traffic. Gauge has never gone past second dash in 28 years. Changed out fan clutch last year seem to take care of the problem. This summer it is heating up again. the fan clutch has a little resistance when cold and hot. Shouldn't it be stiff while spinning while hot? Cools down at speed but gauge does move a aful alot when driving. I did just replace sending unit, I do trust the gauge. Pulled water pump last year also just to verify blades were in tact and pining with shaft. I noticed last nigh bubbles in the coolant when hot. Possible headgasket could my fan clutch be bad again?
Engine overheating
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08GT500
5 Year Member
Hi,
Sounds like you may have more than one problem, I’d still confirm with a mechanical gauge if no other evidence of high temperatures exist. Thermostatic clutch ass’y should be spinning the fan with vehicle at rest and low speeds, & when hot- until increased vehicle speed and external airflow picks up.
If the temperature is leveling off at higher vehicle speeds, that would suggest temp. should also be maintained at lower speeds with adequate airflow across the radiator which the fan should be providing.
That sounds as if the thermostatic clutch assembly may not be functioning correctly.
But, it seems it’s fighting abnormally hard to drive temperatures down, as you described.
I Suggest first acquiring a Hydrocarbon test kit to prove if you indeed have a combustion leak path into your coolant.
A small leak may not always blow the pressure cap, I’ve seen radiators blown wide open as a result of this. Test or replace the Cap for safety if a leak is detected in addition to other repairs.
If no HC’s are present, refocus your efforts on the cooling system, thermostat, shrouding, clutch fan ass’y, obstructed engine coolant passages, lean conditions, spark timing, etc.
Please post your findings, and any other questions.
Best of luck!
-John
Sounds like you may have more than one problem, I’d still confirm with a mechanical gauge if no other evidence of high temperatures exist. Thermostatic clutch ass’y should be spinning the fan with vehicle at rest and low speeds, & when hot- until increased vehicle speed and external airflow picks up.
If the temperature is leveling off at higher vehicle speeds, that would suggest temp. should also be maintained at lower speeds with adequate airflow across the radiator which the fan should be providing.
That sounds as if the thermostatic clutch assembly may not be functioning correctly.
But, it seems it’s fighting abnormally hard to drive temperatures down, as you described.
I Suggest first acquiring a Hydrocarbon test kit to prove if you indeed have a combustion leak path into your coolant.
A small leak may not always blow the pressure cap, I’ve seen radiators blown wide open as a result of this. Test or replace the Cap for safety if a leak is detected in addition to other repairs.
If no HC’s are present, refocus your efforts on the cooling system, thermostat, shrouding, clutch fan ass’y, obstructed engine coolant passages, lean conditions, spark timing, etc.
Please post your findings, and any other questions.
Best of luck!
-John
I agree with John, not that I have any idea what he usually is say'n but I can get the drift of it 
Now about that stock gauge: every time you change the sender it will react differently, the stock gauge is what I call 'a best guess', add an aftermarket mechanical gauge even if it is temporarily zip tied to the wiper arm so you know what the temp actually is and where it reads on the stock gauge.
Now about that stock gauge: every time you change the sender it will react differently, the stock gauge is what I call 'a best guess', add an aftermarket mechanical gauge even if it is temporarily zip tied to the wiper arm so you know what the temp actually is and where it reads on the stock gauge.
08GT500
5 Year Member
HemiRick
I'd be looking at jacking under the house
Fan clutch should noticeably tighter when hot, if not its bad. Over the years I've had 2 small head gasket leaks on my Mustang. When started it would miss for a minute on the leaking cylinder.
Does the extreme duty clutch have a spring on the face?
I try to get the replacement with the spring, they 'lock up' if the unit stops working.
I try to get the replacement with the spring, they 'lock up' if the unit stops working.
08GT500
5 Year Member
Glad to hear negative HC test. This the one you have installed now?
lmr.com
-John
Mustang Fan Clutch (85-93) 5.0 - LMR.com
Trying to save more power while still keeping your Mustang cool? A Mustang Fan Clutch is perfect for you!
lmr.com
YesGlad to hear negative HC test. This the one you have installed now?
-JohnMustang Fan Clutch (85-93) 5.0 - LMR.com
Trying to save more power while still keeping your Mustang cool? A Mustang Fan Clutch is perfect for you!
08GT500
5 Year Member
Hi,
Ever nail down your overheating issue?
I’d not listed the lower air deflector that directs airflow up into the Radiator/A/C Condenser, helps at those lower speeds quite a bit. Didn’t want to leave you hanging if the issue remained & you’re working at it & wanted suggestions.
Best!
-John
Yes all shields are in place. I flushed this weekend to no avail. Condenser and Radiator fins are clean and open. I am a bit stumped, I ported and polished the head a couple of years ago. I am going to pull motor this winter and dig deep. They are old school J302 heads, I have heard that coolant passages are prone to cracking.
08GT500
5 Year Member
Hi,
Well..that’s certainly sounds like a possibility.
There is one remaining last ditch effort to check with the motor assembled in the car.. Externally pressuring the Blocks Coolant passages using compressed air laden with a tracer dye will help you either way by revealing if a fissure exists, and where the actual leak path is if you need do a teardown.
No oil in coolant or vise versa, heater cores clean, not blowing steam, no loss of coolant, motor runs as it should aside from fighting this Temp rise. Glad to assist if you want to try it. Either way, best of luck!
-John
Well..that’s certainly sounds like a possibility.
There is one remaining last ditch effort to check with the motor assembled in the car.. Externally pressuring the Blocks Coolant passages using compressed air laden with a tracer dye will help you either way by revealing if a fissure exists, and where the actual leak path is if you need do a teardown.
No oil in coolant or vise versa, heater cores clean, not blowing steam, no loss of coolant, motor runs as it should aside from fighting this Temp rise. Glad to assist if you want to try it. Either way, best of luck!
-John
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