By September 2, 2008 Read More →

Engine Overheating – Blown Head Gaskets?


My son recently purchased a Ford Explorer with the 6 cylinder engine. The vehicle has about 130k miles on it and appears to be in great shape. It is overheating. We have read a lot of articles from you about overheating. The low engine temperature sensor came on and we have replaced both of those sensors at the top front of the engine (one wire and 2-wire sensors). We get the same check engine code even after the sensors were replaced and the codes cleared.

We have changed the thermostat. We flushed and refilled the radiator with new antifreeze because the antifreeze looked kind of a dirty brown. The radiator hoses appear to be in good shape and there is no discernable temperature difference and the lower hose is not collapsed. There is no smoke or moisture from the exhaust. It runs fine, but VERY hot. No sounds or leaks from the around the area of the wate! r pump. You don’t smell antifreeze when you check the oil dipstick.

Our friendly neighborhood mechanic says that the overheating must be caused by a cracked head gasket, but there are no leaks and we don’t appear to be loosing antifreeze. I don’t understand how a cracked head gasket cause the overheating without other symptoms. Wouldn’t you expect to see some loss or a mixing of the antifreeze with the oil if it was cracked bad enough to cause this problem.

Should the 2-wire sensor be installed so the metal threads on the sensor are in direct electrical contact with the hole to provide a ground for the sensor? The replacement single wire sensor came with Teflon thread tape, but the 2 wire sensor did not. Does the 2-wire sensor communicate with the computer for control or is it just indication?

Should we consider changing the radiator and/or water pump even though they may be fully functional?

It’s almost as cheap to install a new (used) engine as it is to replace the head gaskets and machine the heads. What would you recommend?



Hi there Mikel,


Since you have read my overheating articles, you already know that the first step is to get a cooling system pressure test to see if you have a coolant leak. If you can open the radiator cap and see coolant at the very top of the radiator neck, you probably do NOT have a leak and can skip the pressure test. If you cant see or touch coolant with your finger (with the engine cold) then get the pressure test FIRST.

Are you POSITIVE that this engine is really running hot and this is not just a dash gauge problem? The dash gauge gets a temperature reading from the temperature sending unit not the two wire coolant temperature sensor…that sensor tells the COMPUTER how hot the engine is, I think you are focusing on the wrong sensor. The temperature sending unit is cheap, and you can buy it at any auto parts store if you want to just make a quick GUESS and see if that corrects the problem.

In my shop I would use a laser thermometer to check the engine when the gauge says it is HOT to make sure the engine is actually HOT. Anything over the normal operating temperature of 210 degrees is too hot. Since this vehicle has 130K miles on the clock and is 12 years old AND you said there was dirty/rusty looking water in the radiator I would be highly suspect of a restriction in the bottom of the radiator….and “flushing” does nothing but remove the dirty water not the actual blockage only a new radiator will do that.

A restriction in a radiator will usually cause freeway speed overheating…just like trying to sprint a 100 yard dash with your mouth closed!

From what you tell me I do not suspect a blown head gasket or an internal engine problem. Any mechanic who just comes to a “…..must be a head gasket” conclusion without testing and checking is NOT much of a mechanic in my opinion and should be avoided.


Austin Davis


Reader Follow Up

Wow, thanks for the rapid response. We know that the engine is “boiling” the antifreeze in the expansion tank connected to the radiator and the engine compartment is unbelievably hot, hotter than any engine I have ever experienced. Both of the sensors have been replaced. The cost for both was $28. The gauge on the dash reads pretty close to the H when its this hot, but doesn’t look pegged. The computer display on the center console says engine coolant OK, even when the liquid is boiling in the expansion tank. I know the engine should not be as hot as it is, regardless of what the gauges indicate.

We may replace the radiator and radiator hoses this weekend because the vehicle is of an age that if he keeps the car and it probably wouldn’t be a wasted effort and the cost is still low enough to be worth the gamble. The only other cooling system component to change is the water pump and it has no apparent signs of being defective. Thanks for your input. I may get back to you if the radiator and hoses doesn’t work.

Mikel Kline


Hello Again Mikel,

I would lean toward a restriction in the radiator then. You can get an aftermarket replacement radiator pretty cheap at your auto parts store. Would be a great idea to replace the thermostat again, they don’t like to overheat like your “new” one has already done.


Austin Davis


Reader Follow Up


Today we replaced the radiator, radiator hoses, thermostat and re-replaced the engine coolant sensor. The aftermarket replacement radiator also claimed to provide 20% more cooling than the original. The replacement sensor cleared the check engine light and the new radiator appears to have solved our engine overheating problem.

The “stock” thermostat is a 198 degree thermostat, so the engine is supposed to run a little hotter than what I am used to but is no longer what I would call crazy hot! Thanks for your advise…I’m glad we followed it and I thought that you might like to know that you were right on the button with our apparent solution.


About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."

Comments are closed.