warm engine gets colder while idling?

yotatoy

Active member
Joined
Sep 22, 2012
Location
Kodiak, AK
TDI
2000 Jetta 1.9 TDI
I have noticed my TDI will not warm up while idling. I just picked up a coolant heater from a friend for free (is new, but he totaled his TDI and won't be needing it). Anyhow. I was driving yesterday on highway for about 2 hours in the cold northern parts of Michigan, engine running right at 190 the whole time. I pulled over to rest, potty break for kids, snacks, etc. Left car idling while doing this to keep heat on for boys (we travel with them in comfy clothes and no coat in warm car). Any how, by time we idled there for twenty mins and were ready to leave, the temp had dropped down significantly (I would guess 120-140).

It seemed strange to me that it would cool down from warm while idling.




Does this seem normal, or maybe a thermostat issue, or....
 

cfa5

Veteran Member
Joined
Mar 14, 2010
Location
Southern AB
TDI
2003 Jetta wagon 5sp
normal for diesel motors to cool while idling in cold climate.

wayne
 

yotatoy

Active member
Joined
Sep 22, 2012
Location
Kodiak, AK
TDI
2000 Jetta 1.9 TDI
That was my feeling after thinking about it. Just caught me off guard. Thanks for the response.
 

Curious Chris

Top Post Dawg
Joined
Jun 11, 2001
Location
Pineview GA
TDI
Jetta Wagon 2003 RIP Rockford IL
Yes at idle aka throttle position = 0% the ECU is mandated to deliver enough fuel to maintain an even idle at 903 rpm; no more no less. And of course it is only spinning the flywheel and that is not enough load so it cools off.
 

kd7iwp

Veteran Member
Joined
Jun 27, 2009
Location
Abbotsford, BC, Canada
TDI
2002 Golf GLS
Geepers! Having never been in a cold climate like that myself I didn't know. I know it doesn't take much fuel to spin the engine at idle, but still, I have a hard time believing that the heat more heat is leaving through exhaust and radiation from the block alone than is being injected with fuel. Considering that it is covered with panels on all sides, etc. Wow. Gas cars sure must be inefficient (which we already know with mpg comparisons)
 

demox

Veteran Member
Joined
Mar 16, 2005
Location
Montreal
TDI
Jetta TDI 2000
I have noticed my TDI will not warm up while idling. I just picked up a coolant heater from a friend for free (is new, but he totaled his TDI and won't be needing it). Anyhow. I was driving yesterday on highway for about 2 hours in the cold northern parts of Michigan, engine running right at 190 the whole time. I pulled over to rest, potty break for kids, snacks, etc. Left car idling while doing this to keep heat on for boys (we travel with them in comfy clothes and no coat in warm car). Any how, by time we idled there for twenty mins and were ready to leave, the temp had dropped down significantly (I would guess 120-140).

It seemed strange to me that it would cool down from warm while idling.




Does this seem normal, or maybe a thermostat issue, or....
Yes, its very normal ...to get the heat back to normal ..all you have to do
is not to use any heating in the car for 5min. or so ..190 will be back
to normal.It can also hapen while driving short dist... due to extreme cold condition
again you shut the heater completely no fans etc..
Also think about the unburned fuel blowing out of the exhaust due to the low engine temp, exhaust smell..etc
Unsafe for the passengers.
 
Last edited:

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, MA. USA
TDI
2015 GSW 6M in S trim the other oil burners: 1967 two stroke Sonett 1988 Bolens DGT1700
I have a hard time believing that the heat more heat is leaving through exhaust and radiation from the block alone than is being injected with fuel.
The major contributor is that the diesels don't use a throttle plate to limit air intake.
Gasoline engines limit the air as well as the fuel. At idle there isn't much fuel, but there also isn't much air let in either.
A diesel cuts the fuel to the minimum, but there's still the full volume of air brought in. The diesel is, in effect, internally air cooled with a lot of cold air coming in, and not much heat being added from fuel.
 
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