Surging Temp gauge.. slow heat

[95Stangv6]

Just lately my temp gauge has been jumping up for no reason. It will almost max out then quickly fall back to normal range. Also the heat isnt working properly. When the gauge drops back the heat is warm then seems to get cool. We have replaced the thermostat and are not sure what to replace next.

 

[silver_sn95_v6]

try another stat, theyre notorious for being crappy. After that check yopur radiator for clogs, or for pinched hoses

 

[Skymarshal]

Your water pump could be worn out and cavitating. Does the temperature fall back to normal when you let the engine come down to idle?
I wouldn't suspect that unless you have a LOT of miles, though. Mustang water pumps aren't a known trouble spot.

Don't mess around with an overheating car! Get it fixed. If you drive it too long in this condition, you're inviting a blown head gasket (especially on a '95 Stang).

 

[silver_sn95_v6]

did yuou get all the air pockets out when you replaced the stat? that could be the issue as well.

 

[95Stangv6]

Yes we did get the air bubbles out of the system, by leaving the cap off letting it run and waitin for the level to go back down.

The temp guage will go up and drop back at random times.. it doesnt matter if you are moving or not.. it will go up while driving then all of the sudden drop back.

It seems a new water pump may have been put on it because they have the blue gasket sealer all around it. Maybe a rigged job tho, its only started lately.

Car has roughly 80k miles

 

[Skymarshal]

You may have a blown head gasket already. Severely overheating an engine can cause head gaskets to fail, but if a gasket fails for another reason, it can cause overheating. If combustion gases are leaking into your coolant, it will raise the temperature of the coolant, and the bubbles will interfere with coolant flow through the radiator.

If you want to make sure your head gaskets are intact, buy or rent a coolant system pressure tester, and pressurize the system to 15-20psi. Leave the car overnight with pressure in the system, and the next morning pull all the spark plugs and crank the engine. If coolant comes spraying out of one or more of the holes, you've got a blown head gasket. Before you drive the car to the shop, make sure you get all the coolant out of the cylinder (s) so you don't get a hydraulic lock!

Best of luck, but its starting to sound like head gaskets. As you probably already know, the '95 is known for that.

 

[95Stangv6]

With a head gasket, shoudlnt you be able to smell burnt coolant in the exhaust, also wouldnt it render performance?

coolant levels arent disappearing either.

No white smoke, and oil looks fine.

 

[Skymarshal]

I suppose with a bad leak, you would be able to detect combustion by-products in the coolant, either by sight or smell. I've heard of leaks that are too small to cause that or affect performance, but are still big enough to cause cooling problems.

I don't think you'd get a noticable coolant loss or white exhaust smoke unless the leak was massive, and the oil wouldn't be affected unless the leak breached an oil passage in the block.

To rule it out, I'd do a pressure test. Maybe a shop can also test for coolant flow and thermostat function, although it will be tough to get it to act up at idle if it's only been doing it on the road.

 

[95Stangv6]

Could it be something to do with the heater core, a valve or something, because the heat will be freezing cold then the heat gets warm and the temp goes down as if the coolant is running throught the system again. then when the temp gauge goes back to normal the heat will get cold once again. over and over.

 

[Skymarshal]

Well, that sounds more like a sticky thermostat or a problem with coolant flow.

I'd try removing the thermostat and drive the car for awhile without it. With an "open circuit" cooling system, the engine will never properly warm up, but it should tell you for sure if the thermostat is working. If the temp comes up to somewhere on the lower part of the scale and stays there (doesn't go up and down), then your thermostat was the problem. If it still fluctuates, put the 'stat back in and check for flow problems (bad water pump, air in the system, etc.)

 

[silver_sn95_v6]

chech and make sure there isnt a kink in a heater hose, or a blockage that it is forcing it's way through

 

[rvbaker9250]

If you find a fix for this please let me know my 92 5.0 is doing the exact thing. Thanks

 

[95Stangv6]

What way would you suggest to check for clog. Short post but maybe important

 

[red ink]

any pics or how-to's on where the heater hoes are? call me a noob my 95 is soaking the carpet with coolant, and has a leak up by the firewall.

 

[95Stangv6]

Well guys I fixed the problem tonight. Apparently my car was overheating and loosing little coolant through the radiator cap. All it took was some doggin it to find out. The coolant reservoir was apparently blocked and the radiator kept getting lower and lower. After i unscrewed then cap you could hear the pressure pushing coolant through the system, then the coolant level went down. So we filled it back up started the car, made sure it was full and filled the tank back up.... After driving for 30 mins the temp gauges stays steadily in the middle and the heat is like living in the desert. rvbaker9250, try checking the little hose running to the top of the radiator also.

 

[95Stangv6]

rvbaker9250, It IS a head gasket problem, my fix only temp. fixed it. The head gasket finally blew. Check your oil, and if you see any unusual steam in your exhaust do NOT drive it. A head gasket does cause our symptoms. I'm afraid my heads have warped. Now my car runs fine untill warm then the valve go to chattering like crazy. Get it check out asap.. oh yeah my water pump seal finally let loose also.

 

[Grumpa72]

Just lately my temp gauge has been jumping up for no reason. It will almost max out then quickly fall back to normal range. Also the heat isnt working properly. When the gauge drops back the heat is warm then seems to get cool. We have replaced the thermostat and are not sure what to replace next.

The only time I had these identical symptoms (non-Mustang), I had a slow leak in the water pump that I didn't notice, and I let the radiator get down almost 40%. As a result, the car gave exactly the same symptoms. It would jump up, until the thermostat opened, then it would settle down, fairly low and then cycle between cool and not quite warm. Once the level was up to norm everything worked fine.

Assuming that your your coolant level is good, then I would ask if you tested the new thermostat BEFORE you installed it? It is not rare that a new part didn't work as advertised.

Gary

 

[95Stangv6]

yes, I replaced the water pump and thermostat because the waterpump went out and i got a thermostat to go with it. We knew it was a head gasket because of the water coming out of the exhaust. We got the heads and everything off and found a blown passenger side head gasket, took the lifters out and found metal from what seems to be a bearing so we have to yank the motor out now.

 

[Mike97gt]

Try to get a 3.8 out of a later car so you have the updated headgaskets.