LaserK04

Hey all-

I've searched the archives extensively for any help relating to my problem, and I've tried every suggestion I've found so far with no success.

The car is a 1997 A4 1.8TQ, 88K miles. It has mods as listed below, but this problem just began as I completed a bunch of service items on the car a day ago: Timing belt, water pump, thermostat.

Since the replacements the car seems to run fine other than that the coolant temp now varies between normal and a little less than 3/4 to hot. it never goes further and always cools back down to normal, then suddenly gets hot again.

There are NO leaks whatsoever in the cooling system.

The cooling system was completely drained and refilled with a 50/50 of G12 and distilled water. I initally assumed it was air in the system, but I followed the bleed procedure at the heater core hose, and there seems to be no change. I ran the car for a while with the return hose to the top of the reserviour disconnected and I did see some bubbles expelled but it appears to be a solid stream now without air bubbles in it. Next I thought, coolant temp sensor, but I just replaced it 3 mos ago, and every time it's failed (4 times now) I've had it read cold, not hot, and it's awfully coincindental that this would occur right after this work was done.

The car's heat seems to be functioning normally, and coolant is cirulating, so I know the thermostat is in fact opening. The electric rad fan comes on with the AC, but I don't see it responding to the indicated high temps, however, without AC. Another thing I've had trouble with is the viscous fan clutch, but the problem is that the fan won't shut off as opposed to not working so if anything the car should run cooler with it working full time. EFK is coming to fix that.

Another thing I noticed is that the system does not seem to be pressurizing to the level it used to. When the car is hot I can pop the reserviour cap and only get a slight hiss, whereas before it was pressurized enough to blow coolant out of the cap. I assumed the air in the system may be keeping it from pressurizing fully, but as far as I can tell it's been bled of air quite well.

This behavior occurs mostly at a steady cruise. What's really strange is that when it occurs, if I drop a gear and increase the revs (hence upping the cooling system pressure) the car cools back to normal in 15-20 seconds, every time.

So far this is what I've come up with...

1) my brand new thermostat is sticking or not opening fully, and the increase in revs is enough to kick it open entirely and cool the car down.

2) air remains in the system. I've followed every bleeding procedure I fouind, including Audi's, in the archives, and it seems to be perfect. Is there another bleed screw besides the heater hose?

3) Possibly a bad cap on my coolant tank not allowing the system to pressurize properly?

Any ideas or advice you might have would be great, because Lime Rock is looming and it can't be running hot!


Thanks!

Tbandido

The dealer has pressure testing gear, may be worth it??

WYSIWYG

with your viscous fan. where did you get the pump/thermostat?
use channel 49 of your climate control and read us the coolant temp/activity

LaserK04

That connection you mention on the radiator is plugged in. Could it be reversed somehow? Most VAG electrical connections I've dealt with only fit one way, and it snapped right on.

Pump and thermostat I ordered from ECS Tuning.

As far as the fan clutch, it just never unlocks, the fan spins all teh time. That would certainly make the car run cooler, if anything.

Whats strange is that if I'm cruising at say, 3000 revs in 5th gear, the temp will rise 2 ticks on the guage and stay there. If I drop to 3rd gear but maintain the same road speed, only increase the rpm's to 4500, the temp comes right down, presumably from a large cooling flow increase. This makes me think maybe my thermostat is sticking, and the sudden increase in flow is enough to kick it open fully?

WYSIWYG

flushing service of the likes of pepboys, they can determine if your thermostat is working properly - aroun $40 i think. the cyl head water tunnels are very tight - hopefully its not being blocked by a foreign body.