I have a 1997 f150 xlt. Lately when I start up, the temp. guage will proceed to climb to normal and then drop to cold. Within a few seconds it will red line to hot, stay there for about 10/15 seconds and then drop back to normal. After it drops back to normal it runs fine and everything is normal. It appears to happen on first starts when the engine is cold or cooled down.
I have not noticed this during the summer months but only the cooler months and winter here in Wisconsin, when the heater is in use. Also when this happens coolant is blown out of my bypass. I assume this may be because of red lining to hot. I am not much of a mechanic so I'm not sure.
Is there anyone out there who may have had a similar problem and/or knows the problem I'm having and can help me out?
Any assistance would be greatly appreciated. My mechanic can't figure it out and it's driving me nuts.
Thanks.
pdubs4143

 

Probably you will get more responses if you post this in the engine forum.

But for what it's worth, it sounds like combustion chamber leakage into the cooling system (ie, blown head gasket and/or cracked cylinder head)

It should be easy enough to diagnose if your mechanic has the proper tester...

http://buy1.snapon.com/catalog/item....re&dir=catalog

You have special adaptor that goes on in place of the radiator cap...it has a hose attached with a pump-bulb inline that you squeeze to draw air out of the cooling system, into a little bottle filled with a specialized test fluid. The fluid is blue. If ANY hydrocarbons are present in the air being pulled from the cooling system, the blue fluid will turn green, indicating that the combustion chamber is definently leaking into the cooling system. In other words,
green = off come the cyl. heads
to find and fix the problem.

I would think to get this test done, probably run you about 60 bucks retail at a shop.

 

I'll revive this thread since you've described the symptoms I'm experiencing now on my 2000 5/4L with 126k. Thought it was a related to a bad thermostat and replaced it only to find the symptoms persist. Going into the shop this week. It seemed to boil out the fluid after a while especially during the transition time from cold to hot. Also running rough under load at idle. What's involved with the fix if it is in fact a head gasket? How big a job to replace?

****

 

If it is indeed a cracked head or head gasket. In short, you've go to pull the spark plugs, remove everything in the front that is bolted to the heads, remove the valve covers, remove throttle body w/ the intake, remove exhaust manifold, remove head. It's a full one day job for a weekend mechanic, little longer than that with all hand tools.