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I hope I'm posting this in the right area. If not, I'll go ahead and apologize up front!
A friend has a 3.8 that exhibits some strange occurrences (to me, anyway) in that the temperature gauge fluctuates from perhaps 1/4 of the way to within an eighth of an inch of HOT. This will occur over a matter of ten seconds. It will stay there for maybe 20 seconds, then start dropping down to half gauge, almost as rapidly as it climbed. Makes no difference if the engine is idling, running 2500 rpm down the highway at 75 mph, ambient temperature of below freezing, or like today, 75 degrees.
I have in the past several days replaced the thermostat with an after-market , then official Ford 195 degree unit, installed a new temp sending unit and topped-off the coolant. I had convinced myself that the new non-Ford thermostat was defective, installed one from my local Ford dealer, and then "stove-top" tested the aftermarket one, which proved to be good.
A little more background and info: When the temperature starts making its climb, the check engine light flashes. Once the temp tops out, the light stays lit and will stay on until the engine completely cools--like the next day.
Another issue he will have to deal with in the near future is that he continued driving the van after it had cooked. It has a all-too-typical front seal leak and he failed to add coolant to the overflow one time too many. I haven't bothered with the true checks for a blown head gasket; I can smell exhaust gases in the overflow tank, and see the white exhaust out the tail pipe. A rough idle combined with the above convinces me he has a blown head gasket.
Can anyone give me an idea of what is going on in this cooling system that can cause the temp gauge to fluctuate so rapidly from cold to hot, back to cold in a matter of seconds?
Thanks for any help!
A friend has a 3.8 that exhibits some strange occurrences (to me, anyway) in that the temperature gauge fluctuates from perhaps 1/4 of the way to within an eighth of an inch of HOT. This will occur over a matter of ten seconds. It will stay there for maybe 20 seconds, then start dropping down to half gauge, almost as rapidly as it climbed. Makes no difference if the engine is idling, running 2500 rpm down the highway at 75 mph, ambient temperature of below freezing, or like today, 75 degrees.
I have in the past several days replaced the thermostat with an after-market , then official Ford 195 degree unit, installed a new temp sending unit and topped-off the coolant. I had convinced myself that the new non-Ford thermostat was defective, installed one from my local Ford dealer, and then "stove-top" tested the aftermarket one, which proved to be good.
A little more background and info: When the temperature starts making its climb, the check engine light flashes. Once the temp tops out, the light stays lit and will stay on until the engine completely cools--like the next day.
Another issue he will have to deal with in the near future is that he continued driving the van after it had cooked. It has a all-too-typical front seal leak and he failed to add coolant to the overflow one time too many. I haven't bothered with the true checks for a blown head gasket; I can smell exhaust gases in the overflow tank, and see the white exhaust out the tail pipe. A rough idle combined with the above convinces me he has a blown head gasket.
Can anyone give me an idea of what is going on in this cooling system that can cause the temp gauge to fluctuate so rapidly from cold to hot, back to cold in a matter of seconds?
Thanks for any help!
