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Low Coolant Temps in My Mk4 TDI Jetta
by
Toby
on 09 Jan, 2014 06:20
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I am having trouble with low coolant temps with my 2000 TDI Jetta. Th gauge does not come off the peg unless I drive it hard for an hour or so. Cabin heat seams to work but it takes a long time to come up to temp. This is all at 45*F. After a 3 hour drive I can still put the back of my hand on the top radiator hose. Fuel mileage is way down (37+/-). It has a brand new 92* C thermostat in it. The second one since I got the car in June. After I replaced the first one in July the gauge read mid scale, then as ambient temps dropped so did my coolant temp. I doubt that its the temp sender. A 197*F I should not be able to touch the back of my hand to the hoses. The VagCom said I was at the magic 80*C when I checked the timing. No relevant codes.
Any idea where to look?
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#1
by
theman53
on 09 Jan, 2014 07:15
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Odd you have already done what I would suggest which was T stat. They are known bad items in these cars. Did you boil it to see if it was working? Really sounds not related but just wondering. I am not too familiar with it but is there a way that something could be in there bypassing the t stat and not letting it get cold?
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#2
by
libbydiesel
on 09 Jan, 2014 11:14
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Thermostat. I got three bad new ones in a row once...
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#3
by
rodpaslow
on 09 Jan, 2014 12:00
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Since I live were it has been really cold for a while (-30 or so, lower if u include wind chill); I would try covering up the rad and take it for a drive. Temperature should rise. My current DD is a 1.6TD, around city it rarely gets over 150°F or so depending on what I'm doing. Highway speeds it's fine.
If it doesn't temperature doesn't rise at highway speeds, I'd definitely test the thermostat as per theman53.
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#4
by
745 turbogreasel
on 09 Jan, 2014 16:06
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Go to harbor freight and get the $25 IR pyrometer. If coolant is leaving the thermostat housing at much less than 195, replace that thing again.
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#5
by
Toby
on 10 Jan, 2014 03:24
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Go to harbor freight and get the $25 IR pyrometer. If coolant is leaving the thermostat housing at much less than 195, replace that thing again.
That was my first thought, until I read that the Horror Fright IR thermometers can be off by 75* F. It would give me a relative reading I guess. I will block the radiator tomorrow when I go out and see if I get a reading on the gauge. I was going to do that before but couldn't see an easy way to get some cardboard to stay in place.
The fact that these have known problems leads me to believe that it may be a manufacturing defect. It would only take a slight flaw to screw up the function. Just a slight leak. I suspect all of the aftermarket units come from the same slave labor camp in china. Maybe I will step up and get a real VW part.
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#6
by
745 turbogreasel
on 10 Jan, 2014 04:15
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I've had pretty poor luck with DOA thermostats of every brand. Trust your diagnostics not the parts list.
I haven't personally tried the HF gun, I went above an beyond for a customer, and he got me a nice one.
Still, your hand is ~90, and a pot of just boiled water is ~210, so it's easy to know how far off the gun is with respect to rad temps.
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#7
by
libbydiesel
on 10 Jan, 2014 10:28
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Just for reference, blocking the radiator will not affect the temperature of the coolant entering the engine unless your thermostat is bad. It can change the operating temperature of the engine some from blocking cold air from blowing over the engine itself, but if functioning properly, the thermostat will very accurately control the temperature of the coolant entering the engine right up to the point that the thermostat is wide open which only occurs in hot weather under significant load.
Do you have the insulated engine cover installed?
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#8
by
Toby
on 14 Jan, 2014 04:17
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Does the cover matter for anything other than sound deadening?
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#9
by
libbydiesel
on 14 Jan, 2014 09:55
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Yes. The cover makes a significant difference in how quickly the engine warms up. That said, if the thermostat is working properly then it should come up to temp faster than you say it does. My '02 wagon gets right up to 190° fairly quickly and stays there rock solid regardless of how gentle I am with it.
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#10
by
Toby
on 14 Jan, 2014 14:17
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As far as I can tell, it never does get up to temperature. I bought a German thermostat and temp sender from Bora that I will install here in a bit. Can't beat their service. Ordered at 3:00 pm here 10:00 am next day. The Wahler t-stat has a rubber gasket in the works, to my surprise. It would seem that getting all the flow shut off when cold is important.
Film at 11:00.