94-95 Mustangs Cooling System Diagnostics
From Mustang-Tech
Overview
General Cooling system diagnostics. For any questions, corrections or concerns, please contact HISSIN50.
General system dynamics; troubleshooting
If the car is running what is deemed to be too hot, the temperature must be checked with a real gauge. As an alternative (better yet, as a back-up), the ECT reading can be interpolated.
Generalities: If you have recently had the cooling system open, ensure air is bled out of it. Erratic gauge readings which sway much faster than one would think possible is a sign of air in the system.
If a car runs hot at speed: -Ensure the coil (radiator) is not clogged with debris. In general, the OEM radiator isn't all that great if: it's got some years on it, one lives in a hot climate or the car has some mods done to it. For most folks, two or three of the above are true. In very hot climates (seeing 100+*F temps) this author believes that any 94-95 can benefit from an upgraded (performance/aftermarket) radiator. In milder climates and non-daily drivers, a stock replacement has reportedly worked well for some if their previous radiator was simply very clogged. -Ensure the air dam is present under the car.
If the above is true and the car becomes even hotter and struggles to cool down with the A/C being on, that can suggest the coil is simply unable to reject enough heat. A new and/or upgraded radiator is often the best move from a monetary standpoint (as this allows an upgrade at the same time. Nice for hotter climates or modified engines).
If a car runs hot at slow speeds or while stationary, but cools well at speed (40 mph +): -Ensure the cooling fan is up to par. The stock 94-95 GT fan is a two speed unit. Low speed comes on at ~208*F. High speed comes on at ~228*F. To check if the appropriate fan is being triggered by the computer: To check low speed fan operation, look for 12 volts at CCRM pin 14 with ECT temps greater than ~208*F To check high speed fan triggering, look for continuity to ground at CCRM Pin 17.
Please see here for further CCRM diagnostics.
There is a fuse for the fan in the underhood fuse box so don’t forget to check it. There is also an EDF fuse. Don’t forget about it either.
-If the car cools decently while going slow for a bit but then heats up until shut off and restarted later (where this cycle repeats), check to see if a circuit breaker was installed on the fan harness. When thermal thresholds are reached, the breaker opens, turning the fan off.
The fan connector/interface itself was known for heating excessively. Unclip the fan connector from the fan motor and ensure that the connector itself and wires and terminals don’t show signs of overheating. Often times, this is overtly evident. Some cars have a circuit breaker retrofitted to the fan connector. If it seems like the fan stops working after a bit of operation, see if this breaker has opened the circuit. This has been known to occur (the breaker was an attempt to keep fan motors/wiring from overloading and catching on fire).
Many desire to install switches to control the fan speeds manually. One would connect CCRM Pin 14 to twelve volts via a switch for low speed switching. One would connect CCRM Pin 17 to ground via a switch for high speed fan operation. Do not run both speeds at once (either via the switches or accidental clashing of one fan switch and the OEM control). A write-up for this modification exists here
If you should decide to do away with the OEM fan control, which many do as it leaves quite a bit to be desired, a soft start or variable fan controller is a popular and wise option. Flexalite, SPAL and Dc Control all offer such controllers. This user chooses to use a Dc Controller (www.DcControl.com). It uses pulsewidth modulation to provide infinitely variable fan control. I have used the controller in 115*F ambient temps while stuck in traffic and the unit excels.
Don’t overlook your thermostat. A performance thermostat is well worth the few extra dollars one costs. I’m familiar with the Mr Gasket line, which is a quality piece. It is fully balanced, which means it doesn’t suffer from hysteresis as inferior thermostats can. It opens fully sooner and includes a jiggle valve to help the system self-bleed.
Ensure the system is holding adequate pressure. Each PSI in the system raises the effective boiling point almost 3*F. A 16 PSI cap raises the effective boiling point over 40*F.
A common misconception is that more coolant will allow greater cooling. Water rejects heat ~2.6 times more effectively than ethyl glycol coolant. Coolant itself is useful for freeze protection, raising the boiling point (which is partially offset because the coolant itself is displacing water which could be in the system, so coolant temps might not have gotten as high in the first place), rust inhibition and lubrication. While some folks like to run straight water with a cooling system additive (for rust protection and lubrication), on a daily driver in all but the hottest climate, I don’t like to run less than 30% coolant. If a cooling system needs to run less coolant to function, there are likely other issues at hand which should be addressed.
And always use water deprived of minerals. Distilled water purchased from the store or premixed coolant and water solutions are common ways to achieve this. Some people like to use products which reduce surface tension (Redline and Royal Purple, for two, offer such products).
