overheating question???

[dyoungen]

I have a N/A 1985 Jetta backed up by a manual 5 speed. About a week ago the red flashing (temp) light came on and the temprature gage started climbing till I pulled over. I popped the hood and looked everything over, no problems, no leaks. I removed the coolant tank screw on cap and released the pressure. The tank had plenty of coolant so I figured no problem. I drove it a few times the next few days with no problems. This morning the same thing happened. I popped the cap and released the pressure. I got back in and drove around 70 miles without any problems both days. Am I looking at a thermostat problem or a cap problem? Both times the temp gage registers the same as it has since I bought it when I"m driving it with the a/c on or off, like right now.

[DCC]

I have a N/A 1985 Jetta backed up by a manual 5 speed. About a week ago the red flashing (temp) light came on and the temprature gage started climbing till I pulled over. I popped the hood and looked everything over, no problems, no leaks. I removed the coolant tank screw on cap and released the pressure. The tank had plenty of coolant so I figured no problem. I drove it a few times the next few days with no problems. This morning the same thing happened. I popped the cap and released the pressure. I got back in and drove around 70 miles without any problems both days. Am I looking at a thermostat problem or a cap problem? Both times the temp gage registers the same as it has since I bought it when I"m driving it with the a/c on or off, like right now.

When this happened, were you able to check if the radiator was hot? If it was, then it could be the cap. If it was cold, then it's a stuck t-stat.

[dyoungen]

No, I didn't think to check the radiator. Next time it happens I"ll check. THANX!!

[Smokey Eddy]

My solution to this is to take the cap off and look inside it. You'll see the breather thing inside it is sealed with a fairly thick rubber ring. Is this ring way back in the cap? or is it in it's seat where it's meant to be?

if the ring is in the back of the cap i would replace that ring as IT is the problem not the cap it's self. The rubber rings stretch over time and don't offer the pressure retension as well as they do new.

If your rubber ring is in it's place in the cap i would not hesitate to swap out that thermostat for a new one.

drain at the bottom hose at the pump. Once that's done making a mess undo the plastic thing that you pulled the hose off of. Two 10mm bolts i believe.
Once you have that off keep an eye out for the appropriate rubber gromets that wil be in there - i say this because your new T-stat will come with one but the plastic flange the hose comes off of has it's own rubber ring and may not be included with your new T-stat. The T-stat should be clearly visible behind that plastic 90 piece you just removed. you may have to give it a liberal tug to get it free. MORE coolant may come out at this point furthering the magnitude of the mess you've created (at least this is how it goes when i do this ...)

and you can swap in your new one you've of COURSE tested in a pot of boiling water

re-assemble and fill from the top of the rad and expansion tank. Takes a while to get the bubbles out though. Your light may flash in the dash for a good number of kms, ahem, miles! after this.

[dyoungen]

Well it did it again. Red light started flashing and the gage went up. I shut it down immediatly and checked the radiator. It was hot already so I guess I"m looking at the cap, happily, instead of the thermostat.

[DieselBalz]

I know I am bringing up an old thread, but since the search worked so well I didnt feel the need for a whole new thread.

The above is exactly whats happening to me, save for one thing. The factory gauge goes up to half way and stops, but the temp light starts flashing.

I popped the cap and released some pressure. Let it sit for about fifteen minutes than drove it home (interstate), the gauge and light behaved, but the gauge did seem to run on the cooler side.

Let it sit for an hour or so than started it up and let it run for about five minutes. Undid the cap and there was no popping of pressure, but, it looked like the coolant was boiling as it was steaming. Looked at the gauge, it was half way, and the temp light was flashing. Rad was hot, top hose was hot, bottom hose luke warm.

From what I have read, this should be resolved with a new cap/oring? Thanks for the confirmation in advance.