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Jul 5, 2013 | 02:40 PM

migvil

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need help

i have a 99 expedition. while driving temp gauge will go to red but engine does not seem to be overheating and does not go into limp mode. if i let of the gass gauge will go back to normal i have replaced thermostat but didnt seem fix problem. wondering if anybody has had similar problem or help with what could be the problem?

Jul 5, 2013 | 11:03 PM

alloro

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Have you replaced the coolant temperature sensor yet?

Jul 5, 2013 | 11:08 PM

migvil

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thanks

Well not yet but that was my next guess. We'll try that. . Just noticed though heater is only blowing warm air never gets hot maybe another indication of something else

Jul 6, 2013 | 09:28 AM

alloro

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Quote:

Originally Posted by migvil

Just noticed though heater is only blowing warm air never gets hot maybe another indication of something else

This coupled with the high gauge reading could mean air in the system.

Jul 6, 2013 | 03:08 PM

migvil

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Thanks so much for the advise alloro. Im going to clean and flush system before I try sensor.Will that help with any air in system?

Jul 7, 2013 | 12:56 AM

alloro

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Quote:

Originally Posted by migvil

Im going to clean and flush system before I try sensor.Will that help with any air in system?

No, it could actually add more air in the short term. Normally air doesn't enter the cooling system unless it is taken apart, or if a head gasket has blown. So just as a heads up, having air in the system could be a sign of a bigger issue.

Jul 31, 2013 | 09:35 AM

38Chevy454

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I have the same issue, the temp gage would spike, when warming up. Heater would go cold. Caused by air (really it is combustion gas) getting into cooling system, which allows an air pocket at the thermostat. I confirmed the combustion gases with a test kit you can buy. I assume it is a leaking heads gasket and not a cracked head. Mine stops leaking the combustion gas once warmed up.

I "fixed" mine by drilling a couple small holes in the thermostat which allows the air to escape. Yes it takes slightly longer to heat up as some coolant also gets through the holes. Heater may be a bit less warm when it is really cold (15F or less)., but it still blows warm, just not real hot.

When mine is warming up I sometimes hear what sounds like rushing water in the heater core. This is the air being flushed out, as the heater is the high point in the cooling system. With the big PITA job to replace the head gaskets, I have no intention of doing more than my current fix which has been in place for a couple years now.