+What about your hoses? Did you replace all of them?

 

What he said.
Sometimes air bubbles are stubborn and will not come out when you want them to.

 

I will throw my $0.02 in and say (x3) that while a Volvo 940 is a totally different animal I have a great deal of experience with them and this was a very common symptom after a coolant change for any reason - when the sensor for the gauge would become air-bound as a bubble surrounded it the gauge would momentarily shoot up all the way and then settle back to normal just as quickly as the bubble passed. I would bet that you have nothing to worry about.

 

IMHO the space between the gauge stat, the ECU coolant temp sensor, and the actual mechanical thermostat is so small (and turbulent) that a bubble on just the gauge stat would be hard to keep in place, certainly while driving. See pix, gauge stat is the one with a single wire, coolant temp sensor is the one with the square plastic top (two wire). You can feel the end of them if you reach inside the stat hole.

I would suggest a 1/8 inch hole drilled in the stat flange (old school method) or one of those jiggle devices mounted at 12:00 position, that keeps the trapped bubbles from making the stat live in a steam bath.

 

These things are about as difficult as my DOHC 3.4L V6 Chevy Lumina when it comes to air in the coolant system...you think you got it all, and then the temp gauge starts swinging back and forth like a pendulum LOL!

 

Actually, you forgot to burn the boxes that the repair parts came in as part of the offerings of thanks to the Rover gods after getting 450 miles on a tank of gas.....

 

Sorry it's taken so long to reply...busy weekend.

450 miles on a tank...ha! I wish. No, just filled it up for the second time. Got 217 miles on 18.75 Gal (11.57 mpg) on this one.

After installing the rebuilt radiator I 'burped' the system per the instructions found on the forum. That is I had the right front elevated with the cap(s) off, etc. I have had no issues like this at all but many of you are saying there can be a lot of trapped air so I hope you are right. I guess the gauge cycling rapidly does support this thought.

I have the white replacement expansion tank. I did not use any sealant when installing the valley pan gasket other than on the ends as directed. I have a new 180 t-stat with a 1/8" relief hole drilled and installed at the 12:00 position.

I have not replaced the hoses. The idea of air entering the system through bad hoses is interesting. I just saw that AB has the entire set for $99 so that's now on the way.

I've inspected everything and all I found was a drip of green coolant at the bottom of the hose that comes down from the expansion tank. The hose clamp is tight. There doesn't appear to be any cracks in the tank but the coolant is obviously comming from somewhere.

I'm going to jack up the right front today and let it run. I'll try the burping sequence again while I wait for the new hoses to get here. Then I guess I'll get to do it all again!!

Thanks for all the advice guys. Hoping for the best...

 

Update: Drove into town today after attempting to 'burp' again. BTW, nothing was gained on the burping...no bubbles, fluid level topped-off and remained so.

After a mile or so the temp gauge ran from 9 to 10:00. It only stays there for a few seconds then right back down to 9:00. So I timed it and it was pretty steady at this cycle every 35-40 sec though the travel of the needle reduced to just a needle-width or so. I also noticed that everytime I take off from a stop, the gurgling is heard under the dash. If I turn and leave the stop at the same time, the sound is louder.

Got to my destination and parked it. Came back out after sitting for 1.5 hours and checked all the fluid levels, everything was fine. Temp is 15 deg F.

On the drive home, same story but now the gauge goes almost to the top of the 'normal' range every 35-45 seconds of steady driving (55-60 mph). This time the travel of the needle essentially remained unchanged. The occilations continued this way unto reaching home.

I put it in the garage-door with the front just inside and higher than the rear. I then jacked-up the pass front wheel and opened everything up. All levels were completely normal. I let it run for almost 20 min and never saw any bubbles come out or the level drop at all. The oil still looks clean, there are no coolant leaks or drips underneath.

Thoughts?

 

Replace thermostat. It is cheap, and who knows how accurate. Spring end goes inside block (you knew that, but Bubba two years from now might not). Or pull it and test in a pan on the stove (pan must be approved by SWMBO). When you fill the system, do you have the plug out of the top of the radiator? I always wonder if that plug could be used with a small valve to allow a clear hose to be attached so you could valve off the bubbles until a steady stream was coming thru (and re-use the coolant that comes out). And don't forget the small hoses from the passenger side of the radiator (throttle body heater, etc.). You certainly seem to have air in the system.

 

Well the t-stat shouldn't affect the air getting into or trapped in the system should it, especially with the hole drilled? I could see changing it out based just on the erratic operation of the gauge but the heater core noise is concerning to me. I have driven it for weeks without this problem so the suddenness has me a bit worried.

When I bought this t-stat I boiled it and it worked well. I did take the first one I bought back because I felt it was not opening quickly enough and didn't start to open until way after the rated value.

Yes on the radiator plug. It's out while I play the silly reindeer games. I like your idea SB. Kind of like bleeding brakes. What's odd is the tank never does flow over. I can leave it running at idle indefinitely and it will never surge out. Perhaps because it's so cold here?

The other odd thing that I noticed today was I didn't see any flow while peering into the rad. I seem to remember there being a constant flow and you had mentioned there should be due to the throttle body heater. Does coolant flow through that system all the time regardless if the t-stat is open or not? The hoses don't seem to get that warm. May be related...may not.