[Vwdiesel] VW Diesel engine running too hot (fwd)

[Val Christian]

>   Frankly I've NEVER seen one that ran hotter than the thermostat. 
> Most of the diesels have a hotter than 180F thermostat.  Most are 
> 192F or such.  They're supposed to run on the hotter side than a 
> gasser and as I said before, the gauges are not calibrated so a 
> thermometer in the coolant reservoir is the only way to tell if it's 
> right or not.  

1. A passive IR pyrometer / emissive thermometer, aka "laser thermometer"
pointed at the head will give you a VERY accurate idea of the temperature
of the engine, and if there is coolant in the head, and it is circulating,
it will be VERY close to the temp of the coolant.  If cylinder variability
is not a suspected problem, I try to "shoot" the same spot on the head
for consistency.

You can use the same tool to look at coolant temperatures, by "shooting"
the hoses from up close.

Technically, the emissivity of a Al cylinder head is a little different
from a black radiator hose, and that will account for a small read 
difference in the radiated temperature, but not much, and at car engine
temperatures, the widest variation theoretically is less than 2.3F from
-40F to +280F.  Most PIR devices are adjusted for an emmisivity of 0.95,
which works well in almost all automotive applications.  The exceptions
are when measuring objects like polished chrome coolant parts.

I have several of these units, and in my hand is an Extech IR 201 which 
is a low end unit.  Mine is three years old, and cost $59 when new.  The
same device is remarketed by Sears, and retails at $39.  I've been told
they sell for less sometimes.  The range on this unit is -58F to +518F.
Wider range units, very handy for spot checking external turbine and 
exhaust temps will cost more.  

Other automotive applications include measurement of tire tread temperatures
as an indicator of tire alignment.  AC service (measures duct outlet 
temp, not air temp), bad wheel bearing spotting, dragging brake 
identification, etc.  Home applications include freezer performance 
and localized temperature measurements, insulation effectiveness, etc.

Bottom line, this is a tool that should be in everyone's collection, 
just like a $10 voltmeter.

2. Avoid commonly available thermostats, except in an emergency.  I used
a Standt thermostat, which did not seem as rugged as an OEM.  It wasn't.
The rivet failed, and the plate on it ingested into the water pump, 
immediately blocking flow, and causing a blown head gasket within 
just a few seconds at highway driving speed.  I've NEVER had a quality
thermostat disintegrate like that, and the consequences were extreme,
from my perspective.  Oddly enough, the quality thermostats don't seem 
to cost much more, they are just harder to procure.  Find someplace
other than the run of the mill auto parts store to get your thermostat.

3. I cannot find OEM style thermostats for my A2, with 192F or 195F 
temps.  I've only been able to locate 180F thermostats.  Leads would
be appreciated.

On a diesel, the waste energy is less than on a gasser.  The diesel 
runs on heat (expression).  Keep it as warm as you can, so that it
doesn't over temp.  I like 192F or 195F.  180F is too cool.
Besides, in the winter, you'll have better heat with a higher temp 
thermostat.

Val