ALH running warm

wildn

Well-known member
Joined
Oct 19, 2019
Location
Ventura,CA
TDI
2002 Jetta TDI wagon AT
My ALH seems to be running warmer, I've noticed temps at about 200-240*F max. I read both temp measurements from VCDS and my scan gauge. The worse its been was 243 and I pulled over immediately but there was no temp light on. I may just be overthinking, I know these run warm but how warm is too much.

I'm just a little stumped in the 3 months I did a full coolant flush and replaced the thermostat, ECT sensor, and the flange because the clipped snapped. Then about 400 miles ago I had my timing belt and water pump was done at a Trusted TDI mechanic, so even more fresh coolant was added.
The A/C blows cold and the fans kick on with the key on and the A/C button, is it the fan control module? The fuse doesn't look blown and the connection looks good.
 

realslimshaver

Veteran Member
Joined
Jun 20, 2006
Location
cambridge ontario
TDI
2002 jetta gls tdi
does the heat blow nice and hot sustained for 5 min? (confirms water pump impeller is working)

anyting over 212f for these cars is odd unless being pushed hard up hill in hot weather. 185-205f is more normal. check conditions of the 3 30amp fuses on top of battery and give them a wiggle. iirc I think the fan controller is visible on the underside of the car with the pan off. i have wiggled connections on it to get it to work agian. be sure both your fans are working if you have the 2 rad fan model they should both work at the same time.

can be the thermoswitch the offical temps are {low speed fans; on 197-206 (92-97C), off 183-195 (84-91C) high speed fans; on 210-221 (99-105C), off 195-208 (91-98C)}. there is a diagnostic on the fan system here go to page 1 https://forums.tdiclub.com/index.php?threads/check-your-radiator-condenser-fan-operation-now.242699/

rads can get coated or plugged if people don't change there coolant or if they use hard water can cause scale buildup lowering the heat transfer ability.
 
Last edited:

irvingj

Veteran Member
Joined
Nov 28, 2006
Location
Etna,NH
TDI
2005 Jetta Wagon TDI (PD/BEW)
...And radiators can simply lose their capacity for effective heat transfer after a number of years due to external dirt and/or corrosion. Learned that the hard way while delivering an older Subaru to Berkeley from NH. A replacement radiator totally eliminated the problem.
 

Tdijarhead

Top Post Dawg
Joined
Nov 10, 2013
Location
Lawrenceville PA
TDI
2003 TDI Jetta Daughters Car, 2001 TDI Beetle, Daughters car, 2005 Golf TDI Mine, all 5 spds
I recently changed my thermostat and put a new O ring on my CTS. For the first time ever I got an air blockage, these cars almost never have that happen. I separated the upper radiator hose at the plastic union just to the right of the oil filter cap. I heard an audible pop as the hose came loose and I immediately put it back together and the heat gauge has been perfect ever since.

The engine with a properly functioning thermostat should be rock steady at 190* plus or minus 5*. These cars don’t tend too run warm but cool instead especially this time of year. If your thermostat is old and lazy you might struggle to maintain 170*. The temps you are seeing are way warmer than normal.
 

jmodge

Veteran Member
Joined
Jun 18, 2015
Location
Greenville, MI
TDI
2001 alh Jetta, RC2 5speed daily commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/502's backroad cruiser
Hosing your radiator fins out is good maintenance also, especially if you run dirt roads or areas with lots of bugs or pollen. don't use a power washer, just a low pressure hose, don't want to fold over fins. Fins are another thing to check.
Is it running good?
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
ALHs absolutely do not run warm, quite the contrary. If you're confident the water pump and thermostat are working properly I'd question whether or not the head gasket is leaking. After the car sits overnight squeeze the hose coming off the radiator. If it's hard, that's an indicator of a leaking head gasket, as is air escaping from the coolant bottle when you loosen the cap after an overnight sit.

If you don't have those symptoms I'd suspect the water pump.
 

wildn

Well-known member
Joined
Oct 19, 2019
Location
Ventura,CA
TDI
2002 Jetta TDI wagon AT
I recently changed my thermostat and put a new O ring on my CTS. For the first time ever I got an air blockage, these cars almost never have that happen. I separated the upper radiator hose at the plastic union just to the right of the oil filter cap. I heard an audible pop as the hose came loose and I immediately put it back together and the heat gauge has been perfect ever since.

The engine with a properly functioning thermostat should be rock steady at 190* plus or minus 5*. These cars don’t tend too run warm but cool instead especially this time of year. If your thermostat is old and lazy you might struggle to maintain 170*. The temps you are seeing are way warmer than normal.
The cars temp gauge doesn't move past 190*F but the VCDS graphs it peaking at 220 after a while, same with my scan gauge; usually I pull over once it hits 215 on the highway and let it cool down. I replaced the thermostat recently and the ECT sensor, plus I had the timing belt/water pump replaced but I still cant seem to figure out why its getting so warm, would adding a aftermarket skid plate add to the heating up the coolant?
 

wildn

Well-known member
Joined
Oct 19, 2019
Location
Ventura,CA
TDI
2002 Jetta TDI wagon AT
ALHs absolutely do not run warm, quite the contrary. If you're confident the water pump and thermostat are working properly I'd question whether or not the head gasket is leaking. After the car sits overnight squeeze the hose coming off the radiator. If it's hard, that's an indicator of a leaking head gasket, as is air escaping from the coolant bottle when you loosen the cap after an overnight sit.

If you don't have those symptoms I'd suspect the water pump.
The hose isn't hard its a little squishy and I can hear fluid moving when I squeeze it, It doesn't feel like there is an airlock. I flushed the coolant and then I even had the TB and water pump done.
I'm testing the fans tomorrow but the heat and A/C both work as they should.
Is it possible to trigger the fans on VCDS? or do I have to manually supply power to the fan control module and the fans themselves?
 

Tdijarhead

Top Post Dawg
Joined
Nov 10, 2013
Location
Lawrenceville PA
TDI
2003 TDI Jetta Daughters Car, 2001 TDI Beetle, Daughters car, 2005 Golf TDI Mine, all 5 spds
My temp gauge on the car never moved off 190* either but my ultra blue scan gauge showed up to 223*. Pop the clamp on the upper radiator hose to separate the upper hose from that plastic fitting/union to the right of the oil filter, that’s what solved my air lock problem.
 

rwthomas1

Veteran Member
Joined
Oct 16, 2002
Location
Wakefield, RI
TDI
'03 Jetta
ALH's run cool. The fans will really only run in hot weather, in traffic with AC on. If you are on the highway, moving, there is plenty of airflow already. Overheating on the highway means either the thermostat or the waterpump. Could be an airlock, but that is rare. Replacing the thermostat doesn't mean its functioning correctly. I'd start with replacing the thermostat again. Its pretty easy to do and cheap. If nothing changes, then likely you have a waterpump problem.

RT
 
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