HELP--Another Fluctuating Temp Guage

[Rick R]

I just had my head gaskets replaced on my 94 XLT(which I bought brand new) with 28,000 miles as a result of antifreeze in my oil (a problem I identified 3 times as loss of coolant when the vehicle was under warranty). At that time, the dealer also replaced the thermostat (twice), temp sending unit, EEC coolant temp sensor, and coolant. Before the work, my temp guage was fixed between the 'N' and 'O' but now swings between the 'O' and 'M' and hve been told this is normal by the dealer. I have tried everything I know to determine if I have a problem with my engine and would like to know if I should just live with the temperature fluctuations or do I have a potentially serious problem brewing. I have been told by the dealer that the truck was not working properly from the factory and that the temp needle is suppose to move. Please advise.

 

[Rick R]

It has been over 400 miles since the head gaskets were replaced. The coolant has not dropped at all which indicated that there are no air bubbles in the system according to Ford. Also, the heat blows real hot. The dealer also told me they checked the radiator for blockages while the engine was being repaired and found none. I am still puzzled as my needle still moves like crazy. Could it be something is now wrong with the cooling fan? I don't know what controls the fan except that it appears to be some sort of clutch. Any ideas?

 

[Tech]

Hi Rick

How long has it been since the new gaskets were installed? The reason I ask is because I had a similiar symptom right after replacing both cylinder heads on my '91 Explorer. The temp gauge fluctuated quite a bit for several days until the cooling system worked out all of bubbles trapped in various places.

 

[Longs]

Your fluctuation may be normal, and it could be a function of the replacement thermostat, temp sensor, or even the difference in water/antifreeze proportions in your coolant after it was changed. Based on my general experiences with cooling systems, I can offer a couple of observations:

1) There have been a couple of posts about bleeding air from the system after changing the coolant, which you can probably find by doing a search of the board. The bleeding procedure had something to do with loosening the cap after running the engine for so much time. What I did after changing my water pump on my '93 was park on a steep hill, facing uphill so that the radiator inlet was the highest point in the system, run the truck to operating temp with the cap off, make sure that the radiator was topped off and the overflow bottle had enough antifreeze to keep air from being sucked into the system when the system cooled, then reinstall the cap. I then monitored the overflow bottle over time to make sure that the antifreeze was at the "full cold" line when the system was completely cool.

2) Make sure that your system is pressurizing properly. Fluctuations in system pressure can account for the temp changes. Have your system pressure-tested using the pump tester to make sure that it doesn't leak down. Your radiator cap should also be checked to make sure that it holds the proper pressure. If your system checks out OK, then you install a faulty radiator cap, your system pressure will be off.

3) A final check would be to have the cooling system tested to verify that there's no exhaust in your cooling system, a sign of either a head gasket leak or cracked head. A sample of coolant can be sucked into a tester, which will immediately detect even the slightest trace of exhaust gas in your antifreeze. A very small leak could help contribute to variances in engine temp.

Hope this helps.




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"Whoever said you can't fool all of the people all of the time, was a damn fool" Vincent K McMahon, January 1999

 

[Rick R]

I have "bled" the system of air as you stated in step 1. That did not help, though. I have had the cooling sytem pressure tested but that was before the head gasket replacement--should I do it again? Also, should I have the coolant tested for exhaust even though the head gaskets were just replaced and the heads were x-rayed and showed no cracks? Please advise.

 

[Weatherman]

There's only one letter between 'O' and 'M' on the temp guage. If it is just hanging around 12 O'Clock, then there is nothing wrong. The way a cooling system is designed, it will always fluctuate some. I wouldn't worry about it until it fluctuates close to the "Hot Zone", or a very large spread.

But go ahead and have your coolant tested for exhaust and pressure, it will be worth it for the peace of mind.

 

[Rick R]

The guage fluctuates over 1/3 of the range from between the N/O to between the M/A in NORMAL. It can take up to 60 seconds to move from N/O to M/A but retreats back to N/O in less than 5 seconds and then repeats this cycle of increaing and decreasing temperature with a periodic frequency. Does this seem "normal"?