[Vwdiesel] ideal thermostat temp for 1.6 TD

Val Christian val at mongobird.com
Sat Aug 6 12:26:15 EDT 2005


It sounds like you're running really hot.  When I run a 195 thermostat,
at 1500 RPM, the temp is no more than 200F across the head, including the
sensor area.  The gauge on my 91 reads just a half needle width hot of
the center.

With a 180F thermostat, on a fully warmed engine, at 1500 RPM, without
substantial load, the cyl head temp is no more than 183, measured anywhere
across the front.  The exhaust manifold temp is 785F.  The temp gauge
with the 180F thermostat, and the system stable is about 1/3 up from 
the quarter tick, or about 5/12 of full scale.

At low idle, the temps at the head run a little higher, but by no more than
10F.  If AC is on, and the fan running, there is little change in the
gauge temp.  It will not even move 1/2 needle width.

Based upon your description, I would be suspicious that you do not have
your system fully filled.  Several thermal cycles will help, but there is 
no surefire method I've found to completely fill the system.  I pull one
of the sensors (keep spare 3/4" or 19mm o-rings on hand), and check the
fluid there.

Has the car always been this way, or did it happen after cooling system

BTW, I had a sensor O-ring fail one November, when my son played basketball
in Buffalo.  I was stuck on the toll portion of I-90 with no cooling
system.  It happened 1/3 of a mile from a toll booth, so I managed to 
get a 2 litre soda bottle from their cafeteria, and water from their
sink.  Everyone could care less what I was doing, because it was a 
Buffalo Bills game day, and TVs were on everywhere.  I found some athletic
tape, cousin to duct tape, and made a gasket, loosened the cap to 
depressurize the system, and limped home.  Now an O-ring sits in the 
glove box in a plastic bag.  Essential spare part.  Get some now.

Again, I'd figure you have air in your cyl head, and you need to get
coolant there.  Soon.

I just reread your first note (below) and was reminded of a collapsed 
hose on a GM station wagon that my wife loved, and I hated.  One of the 
inlet hoses had a inside layer get loose, and block flow.  The hose looked
OK from the outside, but after running for a while, and sometimes after
just a jab of the throttle, it would somehow block, and the temp would 
soar.  I eventually bought new hoses for the V-6 (I hate gasser V-6 engines)
and found that mysteriously things worked fine.  Then I went through the
pile of parts and found the separated hose.  

Good luck, and let me know if you get more data.


> Val,
> Thanks for the detailed info.  I have a very good 195 thermostat & a cheesy
> 180 Stant that I bought for comparison.  Tested, the one that I took out to
> check seemed to work OK, but I'd probably replace it anyway (not w/ the
> Stant).  If nothing else, it's a helluva place VW put the damned thing!
> I used an IR thermometer & with the gauge reading almost fully pegged I got
> about 220F at the point where the sensors are mounted where the coolant
> leaves the head.  I assumed that would be the highest temp in the system &
> figured that I could add 10degrees or so to account for error in insulation
> w/ the thermometer.  The thing is that I don't have a real baseline for
> what's normal.  The dash gauge has always varied between 3/4 & full temp (at
> full, invoking the idiot light & buzzer), but without otherwise having the
> traditional appearances of overheating (boiling, etc.)...that's why I got
> the IR gauge, & that's why I want to replace the gauge with an aftermarket
> (preferably mechanical) gauge.  Everything else w/ the car seems to check
> out fine & there's no sign of a head gasket leak (although I've seen it
> failed on other cars with almost no outwardly visable sign....is this
> sometimes the case w/ VW diesels?).   
> Regards,
> Chris
> -----Original Message-----
> From: Val Christian [mailto:val at mongobird.com] 
> Sent: Friday, August 05, 2005 5:13 PM
> To: carstuff at fiataccompli.com
> Subject: Re: [Vwdiesel] ideal thermostat temp for 1.6 TD
> Here's my opinion...and I don't have much data to back it up.
> 1. Run the hottest (195F) thermostat you can.  It will keep you oil free of
> moisture and any diesel, better than a lower temperature.
> 2. In my 1.6 NA (91) I ran a 195F thermostat.  When I went to replace it,
> after 10 years of service, I could only find an aftermarket Standt
> thermostat for 195F.  Bad choice.  The Standt failed, with the back plate
> (valve) coming off and obscuring the waterpump.  Bad news!
> 3. The only high quality (OEM) thermostats I've found are lower temps.
> 4. The 195F thermostat is quite adequate, even when running AC.  Remember
> that with AC, the radiator fan is on all the time.  That's a good deal.  The
> temps stay rock solid that way.  When the fan cycles, as is the case without
> AC running, the temps move up and down.
> 5. In my experience, with many VW diesels over many years, if you have
> "overheating", you have a problem.  The cars work just fine, even in the
> hottest WX.  If you're having overheating, you may not have the system
> completely filled, a head gasket leak, or some other cooling problem.
> 6. One time I thought I had a scaled system, which was overheating.  I got a
> replacement radiator, and after getting the condensor off, found the
> existing radiator covered with dogwood fluff.  I replaced the 12 year old
> radiator anyway, but the overheating disappeared.
> 7. Sometimes thermo switches get "squishy" in their operation, and fire off
> at different temps.  A passive IR thermometer will help verify proper
> operation.
> 8. In selection, I would pick the quality of the thermostat, over the temp.
> I thought I cracked the block, with a failed thermostat.  I didn't but it
> was a real pain fixing everything, and thermostats shouldn't fall apart.
> Best.
> Val
> > 
> > So, i've learned to hate German engineers for hiding the thermostat on the
> otherwise wonderfully designed 1.6 (TD) engine.....  I have a question for
> the collective knowledge & experience here:   What is the ideal thermostat
> temp for this engine?   What I removed when investigating was a VW/Audi
> issue 87C deg thermostat (approx 195 deg F).   I've gotten conflicting info
> from parts sources whether the 87C or a slightly cooler (75C/180F) is the
> correct one for my engine.   The original problem was the appearance (by
> gauge) of running hot & a large enough temp increase with the AC to question
> the integrity of the cooling system.   For mostly rather warm-weathered
> southern US driving, what would be the thermostat to use?
> > 
> > relatedly;  what is the cleanest/simplest/preferred coolant refill method
> ?
> > 
> > thanks
> > -chris g
> > _______________________________________________
> > Vwdiesel mailing list
> > Vwdiesel at vwfans.com
> > http://www.audifans.com/mailman/listinfo/vwdiesel
> > 

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