Overheating after thermostat install

V-DubLuv

Veteran Member
Joined
Dec 18, 2012
Location
Davis, California
TDI
2002 Golf Tdi
Finally got around to swapping thermostats in my Jetta after dealing with slow warm up times and little heat in the cabin. Bought oem parts and went for it.

Pulled the coolant ball and pulled the thermostat and housing. Popped the new parts back in, they can only go in one way, topped off the engine with coolant and went for a drive.

After the drive I noticed there was more coolant in the ball than when I started. I took off the cap and there was a very heavy vacuum/ suction on the tank and the coolant was bubbling. After removing the cap, the coolant began draining out of the ball and it sounded like crackling from coolant going into a sizzling engine block. I've tried burping the cooling system but the lower radiator hose remains empty like there is no coolant getting passed the thermostat.

Is there anything I'm overlooking? Or did I get a bad thermostat that is stuck closed? I've seen thermostats fail "open" as they should, but nothing like I'm experiencing.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
The factory manual used to recommend testing new t-stats in boiling water before installation. Dunno if it still does, but I do. :)

Since that's all you've changed, I might be inclined to at least start there, if only to rule it out.
 

maxmoo

Veteran Member
Joined
Jan 19, 2011
Location
Lakefield, Ontario, Canada
TDI
2000 golf, 2001 golf, 2000 beetle, 2003 wagon, 2004 golf, 2004 jetta, all diesels
Could be the thermostat but it's rare....was it oem?
Or even more likely, IMO,..... these engines are prone to air lock..... are you sure you put as much coolant back in as you drained out?
 

V-DubLuv

Veteran Member
Joined
Dec 18, 2012
Location
Davis, California
TDI
2002 Golf Tdi
It was an ID Parts kit. I didn't drain any coolant except for taking off the coolant ball and Didn't lose a Whole lot since I worked quickly. ( too much effort to drain radiator with a panzer plate and lowered car)

I've done a couple thermostat changes on my golf with no problems. How do I get rid of the air aside from regular burping?
 

maxmoo

Veteran Member
Joined
Jan 19, 2011
Location
Lakefield, Ontario, Canada
TDI
2000 golf, 2001 golf, 2000 beetle, 2003 wagon, 2004 golf, 2004 jetta, all diesels
I use my oil extractor to vacuum most of the air out of the system by connecting it to the small hose at the expansion tank until I get coolant.
 

2many diesels

Veteran Member
Joined
Mar 20, 2011
Location
Nor Cal
TDI
rabbit pickup 1z swap Audi A4 Quattro ALH. 02 Beetle TDI. 99 Golf TDI. 03 Wagon TDI. 914 Porsche ALH t
If you pulled the thermostat you lost coolant. Betting you are not bled out have have air trapped in the system.
 

V-DubLuv

Veteran Member
Joined
Dec 18, 2012
Location
Davis, California
TDI
2002 Golf Tdi
Lost about 1 1/2 cups of coolant. Had the new thermostat clipped into the housing ready to go as I pulled the old unit out, minimal spillage. I'll try to pull a vacuum on the return line in the morning. Thanks for the info
 

pdq import repair

Veteran Member
Joined
Nov 6, 2016
Location
idaho
TDI
09 Jetta
I like to fill the engine through the upper hose till full. Too easy to get airlocks in todays cars, not just VW. Hope the overheat didn't cost you a headgsket.
 

V-DubLuv

Veteran Member
Joined
Dec 18, 2012
Location
Davis, California
TDI
2002 Golf Tdi
Used my mity vac on the return line for the coolant ball until I was able to get some coolant through the line. Started the car and drove around until it was up to running temp but I am not getting any coolant through the return line. Looks like there is no coolant circulating?
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
Used my mity vac on the return line for the coolant ball until I was able to get some coolant through the line. Started the car and drove around until it was up to running temp but I am not getting any coolant through the return line. Looks like there is no coolant circulating?
Drive it some more to see if it overheats.
Stay local just in case.
The dash gauge may say its up to temp but the dash gauge does not follow the ECU temp side of the temp sensor.
I've see it on mine in VAD.
With the cold weather the car may not produce enough heat at idle to open the thermostat.
Last thing if you do not see coolant returning in the small hose at the ball reserve the water pump impeller may not be turning.
Plastic impellers are known for this.
Was the water pump replaced recently.
I might have missed some of this. :)

Rich W.
 

TwinTurboKen

Well-known member
Joined
Oct 24, 2016
Location
ID, USA
TDI
04 Jetta 5-spd TDI
I just did my thermostat last night. I let the block drain out of the thermostat hole replaced the tstat after it stopped draining, put the hose and housing back on and tightened down, rinsed the block with water and a funnel to clean off leaked coolant.

filled up the ball till it wouldn't drain down anymore and squeezed the upper hose and lower hose to help move coolant around and get bubbles out added more coolant as necessary.

then started up the car and used a stick against the seat and adjusted the seat recline forward to push the throttle to hold at 2k rpm and had heat on full blast until the car got to 190° on the gauge while monitoring return line flow and squeezing the hoses periodically.

Took the car on a 45 mile round trip drive last night and no issues. holds solid 190°

You probably have air trapped. I would always leave the lid off the ball, and run the car hood open and throttle held down with a throttle stick or jerry rig something to hold down throttle to maintain around 1.8-2k RPM until the thermostat opens. If it doesn't open you have a problem and will know before it ever gets out to the road.
 

V-DubLuv

Veteran Member
Joined
Dec 18, 2012
Location
Davis, California
TDI
2002 Golf Tdi
Drove around with the lid off of the tank a couple times already. The water pump has a metal impeller on it but the car is about due for another timing belt. I am getting a foamy dribble on the return line at best, car doesn't seem to be over heating although it does smell "hot" if that makes sense.
 

JB05

Top Post Dawg
Joined
Oct 20, 2005
Location
Il.USA
TDI
Golf,2005,anthracite blue
I'm having a similar problem. I changed the t-stat a couple of weeks ago because my Ultra Gauge was reading 195F which is hotter than normal, and during the Summer it would reach 200F if I was stuck in traffic. There is good flow coming out the return circuit of the resevoir, but my lower radiator hose is always cold. Cabin heat is good; so I think I may have an air pocket or a clogged radiator.
I would like to know the OP's outcome.
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
The lower hose should be the colder coolant from the radiator going into the engine.
I wouldn't be worried about 200 F in the summer.
If you get 200 F now I would worry.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
I think that there are differences in t-stats. Wife's car runs about 5 degrees warmer than mine: about 195 vs. 190. Never an issue.
 

Nevada_TDI

Top Post Dawg
Joined
Aug 17, 2008
Location
Reno, sort of...
TDI
2001 Jetta TDI
A while ago I installed a brand new, factory replacement t-stat, and it was bad. Bad t-stats do happen and mine was only a couple of months old when it failed.
 

Shenandoah

Veteran Member
Joined
Jan 9, 2008
Location
Shenandoah Valley, VA
TDI
2005 Jetta Wagon; 2005 Beetle; 2004 Jetta; 2002 Golf (three of them); 2002 Jetta Wagon; 2000 Audi TT->TDI; 1999 Beetle
I ALWAYS check a new thermostat in a pot of water on the stove to make sure it opens. I've had two bad "new" thermostats where if I would have checked them first, I would have saved myself a lot of time and coolant.

Eric
 

dieselnuts

Veteran Member
Joined
Feb 27, 2016
Location
NE CT
TDI
1999 JETTA, 2002 JETTA 2003 JETTA
I put a new t-stat on my 2002 and I was getting the cold lower hose. Now I have oil in the coolant. I think it is a head gasket.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
I put a new t-stat on my 2002 and I was getting the cold lower hose. Now I have oil in the coolant. I think it is a head gasket.
If you're getting oil in the coolant I'd be checking your oil cooler.
 

spanky1

Veteran Member
Joined
Feb 24, 2003
Location
east Tennessee
TDI
Jetta, 2012, platinum grey(6-spd manual)
One stupid question. What Should the temp of the hose connected to the thermostat adapter be? Should it be hot? I’ll post my recent experience with this issue later tonight.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
Lower radiator hose feeds into the t-stat housing- should be cooler. Hot is high, cold is low: or remember it as: heat rises and cold sinks.
 

dieselnuts

Veteran Member
Joined
Feb 27, 2016
Location
NE CT
TDI
1999 JETTA, 2002 JETTA 2003 JETTA
I looked at it again and at looks more like soot. Can I use a EGR coolant bypass kit and leave the EGR cooler still in place? or should I remove the cooler and plug it? Nasty out there I'd rather leave it for spring.
 
Last edited:

JB05

Top Post Dawg
Joined
Oct 20, 2005
Location
Il.USA
TDI
Golf,2005,anthracite blue
OP, any update? I viewed a couple of videos where one tech disconnected the upper return hose from the reservoir with the engine running to purge out the air after changing the t-stat on a BEW. Don't know why this was done, but I tried it on my Golf and did see air bubbles and some foam. The level in the ball did go down some, but I think I still have an air pocket. I also replaced the blue cap since the old one did not pass my pressure test.
 

V-DubLuv

Veteran Member
Joined
Dec 18, 2012
Location
Davis, California
TDI
2002 Golf Tdi
I had a bad thermostat. Popped in a new one and all was good. Deffinitely Going to Check thermostats before installations from now on, a few minutes to test can save a lot of time and headache.
 
Top