Wild Coolant Swings

[Jberger]

Hey folks,Looking for any insight on a coolant issue from today. This is for Q2 (1991 Q45, 142,000 mi)

This morning, while on the interstate, the coolant gauge began to slowly move lower (towards cool) and over the next 10 miles or so, fell to the bottom mark. I'd been on the road for about 20 minutes, hwy speed, in cold weather (30 f) when the gauge began to drop.

The car is garaged, and appeared to be heating normally, no obvious leaks or burps of coolant. I stopped the car and left it until I could return this evening to check it out after my appointments.

Coolant levels are fine, but the overflow bottle was almost empty. A few drops of coolant around the main coolant filler neck. Added distilled water to the bottle, followed the coolant burp instructions and drove it back home. It took 10-15 minutes for the coolant gauge to show warm and almost 30 minutes for it to reach 1/2 (Normal).

My only ideas are:1) The pressure cap is defective, probably loosing pressure as the system warms.

2) Bad sensor, doubtful but possible.

Ideas?

[qship96]

not sure about the loss of coolant,but the low temperature sounds like either a faulty temp gauge sensor,or more likely thermostat failing in the open position,not allowing engine to reach operating temperature.

[Q451990]

I agree with qship96. It's probably a bad thermostat. If you're seeing drips around the filler cap, I'd order a new one with the t-stat. If your filler neck cap assembly looks brass, rather than aluminum, you'll need to replace the entire assembly with the updated one.

The t-stat's rubber seal breaks down over time, so in cold temperatures you'll notice your temp. falling at interstate speeds because the t-stat can't cut off the coolant flow, and there's a lot of cold air moving through the radiator and engine.

When you replace the t-stat, you'll need to order the rubber hose that connects between the t-stat cover and the "sacrificial annode" tube that goes to the bottom of the radiator. If they've never been replaced, I'd go ahead and replace the t-stat cover, hose, and pipe. The pipe will tend to look like it has barnicales growing in it...

Heath

[PalmerWMD]

A sticking tstat.

I had exact same symptoms , replaced tstat now all is fine.

Its important to let the engine stay in proper temp range.I am unconvinced how real and /or significant the coolant loss is if the level proper is good.Just keep an eye on levels and listen for the gurgle noise coming froim heating core ( sounds like from dash) that gives away an underfill condition.

Fred...

[Jberger]

Thanks guys!

[elwesso]

Yep... Replace everything heath said.. I just replaced the stat, and the pipe hes talking about had barnicles... not enough to replace but it has some.....

[VimyJ]

Thermostat.