Wierd Overheating?? Please Help!

[Superdave5.0]

I own a 1995 Gt Convert with a 5.0......... automatic......(no jokes please)

After Ive driven for a while the temp Gauge will spike then go down...........It will repeat this process constantly.

I have replaced the T-stat, and It did not solve the Problem.

Any suggestions??? Radiator?? Relay switch for fans?? (the fans workin) Bleed system again??

Thanks In advance for anything you can offer.

 

[ECU5.0]

do you have an electric fan? but the stock gauge is known to be off and is known to jump around. get an aftermarket gauge and see if it does the same thing. replace the cap. and make sure all the air is out of the system

 

[mjbtv]

Check you temp sender, the wire going to it might be grounding itself. But I'm with going with a manual gage.

 

[twolo4u2c2]

The t-stat is the problem....If you get the the real good one(expensive) too. it will open up gradually as the engine warms up keeping the engine at a predetermined temp. The cheap t-stat really waits till the open temp and open quick until the temp goes down and closes fast giving you the up and down temp reading. As I said the good t-stat keep the temp at a set spot.

 

[nmcgrawj]

The t-stat is the problem....If you get the the real good one(expensive) too. it will open up gradually as the engine warms up keeping the engine at a predetermined temp. The cheap t-stat really waits till the open temp and open quick until the temp goes down and closes fast giving you the up and down temp reading. As I said the good t-stat keep the temp at a set spot.

What brand is a "good" one?

 

[ty-rone]

Get a thermometer, which reads high temp and put it into the coolant and see what it actually reads.

 

[HISSIN50]

is this per the stock gauge? on an SN, IIRC, the low speed fan comes on at 208* and high on at 224*. so when the fan(s) come on, it should cool the car back down pretty quick. have you done the fan mods (fan switches)?

the stock gauges suck. i would install a real gauge and know for sure what is going on.

Twolo, what kind of t-stat are you talking about? a stat with a wax pellet (all of them that i have ever seen) cant open at a variable rate (sorta defies the ability of the pellet). a quality stat will be balanced, open fully sooner and flow better, but in reading your post, it left me with the impression that a 'quality' stat (180* for example) would work like variable fan controller. so it would be able to start gradually opening at say 165* and continue to open as demand was needed. that would involve electronics.

FWIW, i am a big fan of Mr Gasket stats. they are very nice units and are under 9 bucks online at 10 bucks at many local speed shops.

 

[Stang8URMPRT]

If you're getting a "Spiking" on the gauge, that's a sure sign of air in the system. What happens, even with the sucky stock gauge, is when the temp sensor hits air, it goes up REALLY fast, then right back down once it hits coolant again. Air in the system will be MUCH MUCH hotter then the coolant, thus the spike. This happens when the coolant system is not topped off, and if you have major air in the system... I say let the car run for a while with the rad cap off, and add coolant until it's fully topped off... I like to rev it up to about 2000 steadily and then top it off, put the cap on, and then let it come down to idle. Just make sure you got all the air out. Cheapest fix, and more then likely the problem.

 

[twolo4u2c2]

What brand is a "good" one?

there usually about $ bucks or so. Or go to the ford dealer and get the factory one. The good ones are controlled by oil inside the t-stat instead of wax like the cheap ones.

 

[ram360]

If you're getting a "Spiking" on the gauge, that's a sure sign of air in the system. What happens, even with the sucky stock gauge, is when the temp sensor hits air, it goes up REALLY fast, then right back down once it hits coolant again. Air in the system will be MUCH MUCH hotter then the coolant, thus the spike. This happens when the coolant system is not topped off, and if you have major air in the system... I say let the car run for a while with the rad cap off, and add coolant until it's fully topped off... I like to rev it up to about 2000 steadily and then top it off, put the cap on, and then let it come down to idle. Just make sure you got all the air out. Cheapest fix, and more then likely the problem.

That's what I'm thinking too.......