[Vwdiesel] ideal thermostat temp for 1.6 TD
val at mongobird.com
Sat Aug 6 14:20:31 EDT 2005
Chris, see remarks below. I copied to the list, incase there is any
addtional enlightenment there. -Val
> Thanks again. That's all helpful - especially for comparing notes.
> Actually, it's always run warm - maybe warmer now that full summer & full
> 95F humid southern weather is in effect...but I've only had the car since
I understand it's hot and humid, but we get those temps here, or
within a few degrees. It doesn't impact the cooling system, unless
it's real marginal to begin with.
> April. I got it from a friend who basically used it for a rather long work
> commute & he confirmed that it always ran on the 3rd tick on the gauge. He
> didn't use the AC. The odometer says its got 425K miles so there is no wear
> or wear-out issue that I would rule out. That said, one reason I bought it
Good miles! Nice deal on the parts!!!
> (other than the incredible mpg & the fact the same friend owns a salvage
> yard specializing in VW/Audi/etc. & said to just come & get anything I need
> for the Jetta for free) is that it has obviously been maintained well both
> mechanically & cosmetically.
> The thermostat I removed had a hole drilled in it. I usually do this now
> when I am replacing thermostats on FIAT twin cam engines because of the same
> apparent tendency to be left with air gaps in the head & thus hot spots.
> The replacement I have (the good one) has a "jiggle valve" built in for
I guess it's OK to do this. I have the failed Standt in my hand,
and there's no hole there. I have an OEM downstairs, and I
don't recall seeing a hole in it. But in the end, it shouldn't
be a factor in the operating performance, and if it helps
burp the cyl head, great.
I probably wouldn't do it, because I'm often trying to get the
engine warmer. In the winter, I can watch the needle go from
normal to "C" after turning on the heater blower. Putting a
hole in the thermostat might be enough to have the system
chill the passengers in the winter. Frightening.
> I suppose it's very possible it's had an air gap in their for some time & no
> one realized it. Under mild - country - no stop/go use it's fine. Besides
> perhaps pulling the upper-most sensor to fill, is filling via the overflow
> tank the correct method on these engines? Oh, that reminds me that I never
> was able to detect or measure any coolant loss or low level.
A friend who services 2.5L Chrysler gasser engines, says it's one of
the biggest complaints that DIYs have. That cyl head has a plug
which can be opened to burp the air out. Doesn't do a complete
job, in my experience.
> Btw, how do you measure RPM? Also - a basic diesel question - does pump
> timing effect running temp the same way ignition timing in a gas engine
Tuned ear. Timing will affect temp, but not as much as a gasser,
and for somewhat different reasons. It's not a factor.
> It sounds like my gauge may be just fine then. Hmmm.....I may bounce some
> thoughts your way if you don't mind once I get more info. Now, on to some
> other weekend errands...
I haven't done this, but you might try a web/ news group search
for purging air from a cooling system. A local parts house tool
catalog has a vacuum pump to purge air...apparently it works even
with the fluid in the system.
If you can draw a mild vacuum, that might be a try...but there's
some radiator/heating core risk. I don't have experience with this
method..but if it works, it would solve some problems.
I think I'd try starting the system, unpressurized, with the car
on a steep incline, so that the radiator is well above the cylinder
head. Then as the engine warms up, I'd give it some RPMs (3000 to
4000) to get the coolant moving. Heat valve on. See if the stirring
of the fluid, might free up some air in the system. You may see a
drop in the system coolant level, if you get some air out.
> -----Original Message-----
> From: Val Christian [mailto:val at mongobird.com]
> Sent: Saturday, August 06, 2005 11:05 AM
> To: chris granju; vwdiesel at vwfans.com
> Subject: Re: [Vwdiesel] ideal thermostat temp for 1.6 TD
> 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
> 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
> 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
> > 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
> > 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
> > 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
> > 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
> > 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
> > > _______________________________________________
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> > > Vwdiesel at vwfans.com
> > > http://www.audifans.com/mailman/listinfo/vwdiesel
> > >
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