Overheating at 70mph+

[txstang347]

I've been having overheating issues for a while now. The cooling system was in pretty bad shape so I've come to the assumption that everything was playing a role in the temp. At first it was overheating very quickly so I replaced the thermostat. Then, it was over heating at stop lights after about 30 minutes of running around. So I decided to get in there and start replacing bad parts.

The following parts were done so I replaced them:

1. Water pump
2. All hoses
3. Thermostat
4. Radiator cap
5. Used Prestone radiator cleaner (Fluid was actually pretty clean)

Also replaced the timing chain, balancer and serpentine belt while I was in there.

With all of that done she only gets hot now while running on the freeway at 70mph+. When I get off the freeway and sit at a red light the temp comes back down to normal. I'm guessing that the flex fan is no longer functioning as it should? I've had if for about 8 years now and it's worked fine, well up until now I guess.

Any ideas?

 

[liljoe07]

What car is this?

 

[txstang347]

What car is this?

1991 Mustang GT

 

[liljoe07]

Any Mods done, and how are you verifying the actual temperature readings.

 

[stang&2Birds]

After ~30mph, the fan does very little compared to the air flow from the car moving.
My next step would be a compression test, or test of the antifreeze for a sign of an exhaust leak.

 

[txstang347]

Any Mods done, and how are you verifying the actual temperature readings.

Full o/r exhaust and 3.55's is about it.

 

[liljoe07]

And how are you getting the Temp readings?

 

[txstang347]

Off the stock temp gauge.

 

[BK_CAULEY]

Off the stock temp gauge.

that could be a problem in itself right there. our factory gauges arent the best in the world. do you have anyone who would let you borrow an aftermarket gauge?

 

[liljoe07]

that could be a problem in itself right there. our factory gauges arent the best in the world. do you have anyone who would let you borrow an aftermarket gauge?

LOL Just kidding

 

[txstang347]

Agreed, but I'd never had a problem with it before and it seems to have responded to everything I've done and is stable at low speeds so that doesn't make much sense.

 

[time only]

One question someone will ask sooner or later. Do your Mustang still have the radiator air deflector under the car ?

 

[txstang347]

One question someone will ask sooner or later. Do your Mustang still have the radiator air deflector under the car ?

It should still be on there. I don't remember running anything over lately. I'll double check when I get a chance to work on her though.

I read a pretty good variety of resons that this might be happening earlier. It also shot down my fan huntch.

***Fan related problems will _not_ cause overheating at highway speed.***


1-Low coolant level.

2-Restricted airflow to the radiator as from leaves or plastic bags in fron of it, or the plastic under-skirting being broken away (as from running up onto curb-stops.)

3-Restricted flow of within the radiator or hoses. Restricted flow in hoses is rarer, but rev the engine to 2000 to 2500 RPM for several seconds after the engine is fully warmed and look for either radiator hose to collapse. To check for restricted radiator, you can take the temperature of the radiator with a non-contact thermometer in several places or you can open the cap (if so equipped) and look for white deposits. White deposits mean you need a radiator. If your radiator has no cap, remove the upper hose and look in through that opening.

4-Poor heat transfer. Poor heat transfer can be radiator to air (look for missing or greenish radiator fins) or internal due to a high ratio of anti-freeze to water (use a hydrometer) or internal due to scale deposits (with an iron engine your coolant will be brownish, aluminum engines can be checked by removing the thermostat or water pump and looking inside for whitish deposits).

5-Insufficient coolant pumping. Metal water pump impellers can erode over time, especially with excessively old coolant. Plastic water pump impellers can break randomly, and are prone to break if the engine is a Ford Duratec or Volkswagen or if the water pump hasn't been replaced after an overheat. Cheap substandard $5 replacement water pumps have often have a poorly designed impeller that can become dislodged. To check, remove the thermostat(s) and fill the system with coolant or water. Remove the radiator cap (if so equipped, otherwise surge tank cap) and observe the coolant level while rapidly snapping the throttle from closed to wide open. The coolant level should change drastically (more than 1/4 inch) if the pump is good.

6-Exhaust gases leaking into radiator. This is usually caused by a leaky head gasket, but can also be caused by a cracked or eroded engine. Note that GM Quad-4 engines are particularly prone to cracking, and four cylinder Chrysler engines and cars owned by youthful males or Jewish women are prone to head gasket leakage. An electroneic gas analyzer can be used to check this condition, but for the do-it-yourselfer, check with the local parts store or tool dealer for a disposable chemical based detection kit.

7-Boiling. Boiling can be caused by too much water in the coolant, insufficient pressure due to a leak or a bad cap, Partially restricted water jackets, or overheating due to another cause. Presumably, any other overheating has already been ruled out so you might as well check for leaks, then replace the coolant with a correct mix and put a new cap on it. If you have a restricted water jacket, you're going to need the engine rebuilt.