Help me with my temp problems please

[black wolfsburg 99]

So I have had my 2003 VW Jetta for 6 years and never has my car ever hit above the 190 mark. I did lots of logging for timing pull and the log for the water temp was always 100C. Today it was at 108C. I had my drivers side fan go out last week so I replaced it with a Valeo fan off MJM. I removed my upper hose and replaced the fan from the top so coolant came out but very little, I replaced the half gallon that leaked with water. The coolant is still very pink in color. For 2 days it showed normal temps but now it goes from 1 to 2 lines above 190 at a stand still with ac on. I verified the fans run while the ac is on and not one drop of coolant is leaking. I checked the coolant level and made sure there isn't any air in the system. Thermostat was replaced 10K ago and timing belt with water pump was done 25K ago. If I rev the motor alittle at stand still the temp drops back to 190 and slowly climbs again. My thoughts are a sticking thermostat, bad water pump, clogged radiator (but I think unlikely) or the Valeo fan just isn't flowing like the stock fan. What are your thoughts experiences?

Mods are GIAC, 2.5 down pipe, front mount intercooler, 02M swap and a few other bolt ons

[black wolfsburg 99]

I'm going to use the shot gun approach I guess. Doing the thermostat and radiator flush today because the hose going to the thermostat isn't hot even after the car running for 20 mins but the upper drivers hose is hot as hell. I think it might be stuck. I pulled the hose to the coolant ball and verified there is coolant movement so I hope its not the waterpump.

[groggory]

I'm going to use the shot gun approach I guess. Doing the thermostat and radiator flush today because the hose going to the thermostat isn't hot even after the car running for 20 mins but the upper drivers hose is hot as hell. I think it might be stuck. I pulled the hose to the coolant ball and verified there is coolant movement so I hope its not the waterpump.

The water pump failing at the same time seems like too much of a coincidence.

I'm thinking one of a couple things...

1) There's an air bubble in your system...you just haven't managed to get it out yet.

2) Your coolant cap is not holding enough pressure

3) You diluted your coolant too much and now it's boiling point is lower and it created an air bubble for you

...

I had problems like that once. It came from running too much water. I flushed my system and replaced with 50/50 g12/water. Problem was solved for me.

[black wolfsburg 99]

I tried leaving the car running for 30 mins with heater on and squeezed the hell out of the hoses with the radiator cap off. I just replaced the thermostat not that long ago when the coolant neck started to leek with a VW one but since I'm doing the coolant flush I figure its cheap insurance because if it still overheats after the flush Ill lose the new coolant. Ive been driving it for 3 days like this now. I would think the air bubbles would be bled off by now but Ive never had this problem before. I agree that this is a hell of coincidence. Maybe I should just flush the system and save the trouble of replacing the thermostat. I already bought it just it case.

[groggory]

I tried leaving the car running for 30 mins with heater on and squeezed the hell out of the hoses with the radiator cap off. I just replaced the thermostat not that long ago when the coolant neck started to leek with a VW one but since I'm doing the coolant flush I figure its cheap insurance because if it still overheats after the flush Ill lose the new coolant. Ive been driving it for 3 days like this now. I would think the air bubbles would be bled off by now but Ive never had this problem before. I agree that this is a hell of coincidence. Maybe I should just flush the system and save the trouble of replacing the thermostat. I already bought it just it case.

I wasn't talking about the thermostat. I was talking about the coolant cap. The coolant cap is in charge of regulating the coolant pressure.

A common place for air bubbles to get stuck is the heater core.

My dumb trick is messy but works...

Run the engine. Wear thick gloves.

Have the car pointed nose uphill / up driveway, etc

Have your coolant ball a bit above the 'full line'

Unhook the upper radiator hose while the engine is running

Coolant should be flowing out. Let it flow out for a couple seconds, then push it back on.

That'll get any stubborn air bubbles out.

be careful though. Don't burn yourself or get hit with steam when you unhook the hose

[black wolfsburg 99]

Ill give it a try today, hopefully that will fix my problem. Do you recall the coolant capacity? I bought a gallon of G12 today with the thermostat.

[black wolfsburg 99]

I dont know if I had a massive bubble or a bad thermostat but I replaced the thermostat and like magic I'm back to normal temps. Thanks Groggory for the help, I tried pulling the hose before replacing the thermostat but it still would overheat.

[groggory]

Whatever works

[nellush]

I have an interesting problem. My thermostat is new...not a VW...and it gets stuck open allowing the engine to cool to the low 100's (degrees F). Looking to change it soon. Maybe a VW thermostat this time?

Sent from my MB865 using Tapatalk 2

[black wolfsburg 99]

I had that problem with my wifes Passat coasting or going down hills until I replaced it. It cost me $17 at the dealer with o ring for the thermostat for My Jetta today. I dont remember what hers cost.