Water temp problem after thermostat change

[JCviggen]

So I got the car back and it had a timing belt change together with waterpump and t-stat.

At first everything is normal, water temp climbs pretty quickly to 90C. After a little while there it drops in the space of 30 seconds to just over 60C, like the thermostat opens and gets stuck. It stays there pretty much sometimes a little higher sometimes a little lower. Give it the beans and it will rise. At some point during the drive oil was 90C, water around 65 and I pulled away full throttle in 1st, 2nd, 3rd. That was enough to boost water to 75C and after a minute or 2 oil had also crept up to 100C (all from just 1 little sprint) but water temp started to drop again while parked.
The fan runs continuously while the engine is running. One side of the radiator is hot to touch, the other side is ouch nearly burnt myself hot to touch. But temp on the dash is around 70.

Any ideas? I find it strange how quickly oil temp will rise, though water stays much colder...though the radiator is pretty hot and the fan stays on though not at very high speed. Fan stops when engine is off, no after cooling.

After letting it sit there for half an hour I started it again, water temp to 90C where it should be and stayed there while parked for 5 mins. Went to drive, within half a mile temp suddenly dropped to 65 again. It literally takes seconds - the actual water temp cant go down that quick.

http://www.greenringer.net/various/water.jpg

Actually the very first time I drove the car home the w-temp also dropped steeply after reaching 90C....but after a few miles recovered within seconds back to 90. That did not happen today, stuck at 60-65 even standing still it slowly drops.

Ideas? :doh:

[V8weight]

You just have an air pocket in your cooling system, which usually ends up right at the coolant temp sensor in our cars. Your temp sensor is getting nothing but steam. Re-bleed the system by pulling the heater core hose back at the fire wall exposing the bleed hole in the cooling pipe.

[JCviggen]

Thanks, that's annoying.

Does the old trick of reservoir cap off + heater on max + driving do anything? Or is it locked in there until the above mentioned procedure?

[V8weight]

Thanks, that's annoying.

Does the old trick of reservoir cap off + heater on max + driving do anything? Or is it locked in there until the above mentioned procedure?
No, unfortunately you won't get anywhere trying to "burp" the system through the reservoir. You'll need to remove the cowl cover, and pull the passenger side heater core hose back and bleed it through the coolant pipe.

[4everRS]

And it will probably take a while to get all the air out. I think all 4.2's have an elaborate cooling system as far as the water jackets go. You may need to rev it up a few times to get the coolant moving.

[JCviggen]

Did a few runs today and water temp was normal each time. Also oil temp is not going up as quickly as it used to at all after a bit of spirited driving. Seems like cooling has improved so it is most likely due to trapped air. Will get it bled anyway even though its improved.

[JSRS6]

It's not too hard for you to do yourself. I can post a few DIY pics if you want.

[JCviggen]

That's allright but thanks! Today I had the sensor changed, it was as old as the car so a bit overdue. Also the audi pressurized tool was used to remove air from the system. Seems OK now, tomorrow morning's warm up will probably decide if its fixed or not but I think it should be OK.