Engine won't warm up. P0128 Help.

JohnInSeattle

Member
Joined
Apr 18, 2018
Location
Seattle, WA
TDI
'04 Beetle, '04 Jetta Wagon, '05 Beetle and another '04 Jetta Wagon
My 2005 Jetta TDI BEW has never warmed up quickly but over the last few months it has been getting worse to the point it never gets over 120F at any time now.

I've read all the threads on this I can find and have already:
1) Replaced my timing belt and water pump, made no difference.
2) Replaced my thermostat twice with name brand ones, one before the water pump and one after, the second one seems to have made it worse.
3) Verified that the engine is actually not warming up by putting my hands on it after driving, there is nowhere that is too hot to touch except the exhaust and turbo.
4) Verified there is coolant flow in the reservoir at idle.

The upper radiator hose and tank is hot and the lower is cool, I assume this means that coolant is circulating and must in fact, be getting past the thermostat somehow, yes?

Outdoor temps around here range between 40F and 60F.

When I took out both thermostats I inspected them in place before removing them and they appeared to be completely closed, I tested the last one in hot water and it seems to only start to open about 180F.
I also inspected them looking for light leaking around the valve seal, they looked tight.

I have on order, yet another thermostat, Mahle seems to be the best brand I can find TX1587D 87C, and also a new temp sending unit because I can't think of anything else to do.

Any Ideas what else to check.
John.
 

Prairie Chicken

Veteran Member
Joined
Jan 28, 2014
Location
Northern IL
TDI
05 Jetta, 04 Jetta
how is cabin heat?

I've had the same problem before but not as bad, It would only get to full operating temp if running hard during the summer. a new thermostat fixed it.
 

JohnInSeattle

Member
Joined
Apr 18, 2018
Location
Seattle, WA
TDI
'04 Beetle, '04 Jetta Wagon, '05 Beetle and another '04 Jetta Wagon
Very little cabin heat, Takes about 20 minutes before it's worth turning the heater on.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
With the engine warmed up the upper and lower hoses should both be pretty warm.
That would indicate the coolant is not circulating. But the opposite seems to be your issue, it's not reaching the 180-190.
So we got an outlier, you've serviced much of the system. Do heat controls have significant affect? Are ther any coolant passages in the block that can be clogged? Have you tried an alternate method of measuring temperature?
Not much help I know.
 

Prairie Chicken

Veteran Member
Joined
Jan 28, 2014
Location
Northern IL
TDI
05 Jetta, 04 Jetta
Just wondering about your driving conditions - do you have a long commute? If you blast down the freeway for 20 miles does anything change?
 

Nevada_TDI

Top Post Dawg
Joined
Aug 17, 2008
Location
Reno, sort of...
TDI
2001 Jetta TDI
If push comes to shove, there is a 95*C thermostat out of a 1.8T motor that many of us here are running in our TDI's that you could try. I am happy with the results I have gotten from this t-stat.
 

JohnInSeattle

Member
Joined
Apr 18, 2018
Location
Seattle, WA
TDI
'04 Beetle, '04 Jetta Wagon, '05 Beetle and another '04 Jetta Wagon
The engine and coolant are very clean, there is a tiny bit of very fine rust that comes out when I change the thermostat, maybe a 1/2 teaspoon of fine dust in a gallon, the liquid looks clear but I see it on a coffee filter when I put it back in.
My alternate method of measuring temperature was my hand. Tee engine was no where near 190F after 20 miles on the freeway, I could touch it easily.
Turning off the heater seems to not make any difference.
If I go uphill for a while it gets up to about 125F then back downhill it goes back to 115F. It cools down to 110F at idle.

I do have exactly a 20 mile freeway commute each way. No it doesn't warm up

I will try that hot thermostat if the one I have on order doesn't help.
 

super1

Veteran Member
Joined
Apr 19, 2010
Location
NY
TDI
none
Air pocket?
Jack up front of car, Rad cap off & keep massaging Lower radiator hose & keep revs up


Sent from my iPhone using Tapatalk
 

JohnInSeattle

Member
Joined
Apr 18, 2018
Location
Seattle, WA
TDI
'04 Beetle, '04 Jetta Wagon, '05 Beetle and another '04 Jetta Wagon
I should have mentioned, I use a vacuum coolant refill every time and put all the fluid back in, if there is any left of course that would mean an air pocket.

Also I can't see how an air pocket would cause excessive cooling?? Only overheating I think?
 

steve6

Veteran Member
Joined
May 25, 2010
Location
Beaverton, ON
TDI
2003 jetta tdi
Is it auto or 5 speed? has someone changed the routing of the hoses at all that you can tell? The thermostat is the only control for keeping the temp up, unless there is some kinda bypass happening.

Make sure the thermostat is properly sealing when you put the housing back on, if its not water is just going to run past it.
 

JohnInSeattle

Member
Joined
Apr 18, 2018
Location
Seattle, WA
TDI
'04 Beetle, '04 Jetta Wagon, '05 Beetle and another '04 Jetta Wagon
It is all factory auto. they are all the factory molded hoses held in their little clips.
The thermostat with the gasket fits into the block like a cork in a bottle.
It takes a few pounds of pull to get it out.

I very carefully put the new one(s) in and made sure the gasket was seated and not rotated or out of place before putting the housing on.
 

steve6

Veteran Member
Joined
May 25, 2010
Location
Beaverton, ON
TDI
2003 jetta tdi
It is all factory auto. they are all the factory molded hoses held in their little clips.
The thermostat with the gasket fits into the block like a cork in a bottle.
It takes a few pounds of pull to get it out.

I very carefully put the new one(s) in and made sure the gasket was seated and not rotated or out of place before putting the housing on.
I've had plastic from the thermostat housing break off and jam in an open thermostat, kinda annoying but look for things like that.

http://forums.tdiclub.com/showthread.php?t=148452&highlight=thermostat+replacement-tip
 

JohnInSeattle

Member
Joined
Apr 18, 2018
Location
Seattle, WA
TDI
'04 Beetle, '04 Jetta Wagon, '05 Beetle and another '04 Jetta Wagon
That was one of things I explicitly looked for when I removed the old Thermostats. They seemed completely closed when I took the housing off.

My latest thermostat has arrived, I'll boil it up and test it then throw it in and see if it makes things any better.

I think I'll try putting a fine wire or fishing line through the valve then support it in water I am heating and see what temperature it lets go at.
 

JohnInSeattle

Member
Joined
Apr 18, 2018
Location
Seattle, WA
TDI
'04 Beetle, '04 Jetta Wagon, '05 Beetle and another '04 Jetta Wagon
That fixed it.
I tested the new thermostat and it held on to a wire until about 205F.
It now takes 19 miles to warm up but it did get up to 195F eventually.

I read the thread
http://forums.tdiclub.com/showthread...eplacement-tip
and was wondering why they had such issues with the gasket? my gasket was a square ring with a groove that fits over the edge of the thermostat, you just push it in the hole.
The new thermostat, the Mahle, came with just an oring, rather than fight with it, I used the gasket from the last one and got in it in minutes.

I also noticed, watching my scan gauge, the bit about the gauges just being analog idiot lights. The gauge went to 190 when the temp was 130F and stayed right on 190 while the real temp continued to rise to 195F. Wow, I didn't know that!.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
So it was the thermostat not closing all the way?
I think stuck open thermostat would have been everyones interweb diagnosis of choice, but...
Third times a charm!
Great work and thanks for reporting solution!!
 

JB05

Top Post Dawg
Joined
Oct 20, 2005
Location
Il.USA
TDI
Golf,2005,anthracite blue
With the new t-stat, does your lower radiator hose get warm when the SG reads 195F?
 
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