PorKen

The 928 thermostat has basically the same dimensions as used on most Mercedes 3.0/3.2L inline sixes (others too). The Porsche thermostat has a larger rear sealing plate, and may be slightly taller, but with the rubber real seal, this doesn't matter. The rear plate is spring loaded, so the absolute height is not an issue. At some parts places, you may always get the Mercedes part.

I'm going to try a hotter thermostat, 87C, for better effeciency (mileage), but combined with intake isolators, so it may give better HP numbers, too.

Thanks (I think ) to Ernest from NY, for sending me his weird 92C Calorstat (France), which I could not find in the US, but got me started looking.


Notes
-The o-ring included with most thermostat 'kits' are too small
-Early, 78-82, w/o the rear seal may need the large rear plate, 1.9"|50mm?
-Don't use a thermostat with a rear plate smaller than 1.7"|43mm (BMW, Audi, VW = 1.38"|35mm)
-There must always be small hole/valve/jiggler to allow air to vent, some types may not have this
-Thermostats start to open somewhere around their stated temp, and are fully open roughly 7C|20F above
-All the searches below use Porsche 1986 928S and Mercedes 1990 300TE
-Don't put too much faith in the pictures you see online
-YRMV, YMMV


Porsche
75C|167F - 928 106 129 16 (superceded by the 17)
83C|181F - 928 106 129 17
o-ring - 999 701 632 40
rear seal - 928 106 163 00 (83-up)

Behr/Wahler (WorldPAC, IMC)
75C|167F - 116 200 00 15
83C|181F - 928 106 129 17
87C|189F - 110 200 05 15

Beck Arnley (Autozone, others)
79C|174F - 143-0578
82C|180F - 143-0681
90C|195F - 143-0636

Motorad (Autozone, Orielly, IMC)
928 http://www.motoradusa.com/catalog.ph...+FI+N+VIN%3A+B
300TE http://www.motoradusa.com/catalog.ph...962cc+GAS+FI+N

Stant (everywhere)
82C|180F - 13648 (35648)
90C|195F - 13649 (35649)
o-ring - 25271



Autozone
928
180F - Valucraft 27780
180F - Beck Arnley 143-0681
192F - Valucraft 27792


27792

300TE
170F - Valucraft 3527
180F - Valucraft 3528
180F - Failsafe 7248-180 (locks open >280F)
192F - Duralast 15649
192F - Failsafe 7248-192 (locks open >280F)
195F - Valucraft 3529


3528



NAPA
928/300TE
167F - ATM1162000015
180F - THM180
195F - THM280
o-ring - THM1071


THM180

ew928

Never measured how accurate the dash temp gauge was, but that crazy 92 C thermostat made the temp guage needle sit just below the upper white line. Scared the bejeezus outta me the first time I ran with it since the car had gone into repair with a failed to open thermostat.

So now when anyone is stuck in nowheresville with a failed thermostat, they can tell the shop to crosscheck Merc inline 6 thermostats if they can't wait for overnight package from the 928 parts vendor.

PorKen

The thermostat that was on my current '86.5 when I bought it would make it run at the same point, just below the upper white line, but it wouldn't ever go higher. I think it was broken. With a 75C, it was just above the first line, and the 80C runs just below or at the mid point.

I did my highest HP/TQ dyno runs with that thermostat, but in the winter, so the intake air was a nice 70F or less. That's partly why I've been looking for a hotter thermostat.

With most of the dyno runs I've seen with 928s, the numbers go up after a couple runs. Maybe the engine runs too cool, or the oil needs to warm up?

The Stant part numbers interchange between the Merc and the Porsche. The Motorad 'Failsafe' thermostats might be worth trying. They supposedly lock open if the engine is overheating (>280F).

sharknoob

NAPA had one in stock for me but i didnt care for the small looking o-ring that came with it my old one was in good shape i reused it

_Thomas_

Hi in colder weather the water temp. of my car hardly ever increases above the first mark, and I also thought about fitting a hotter thermostat.

Today I found my thermostat has no. Nr. 928 106 129 06 (written 83 °C) which is superseded by 928 106 129 17 - so it is probably quite old?

When the thermostat is cold (room temperature) there was still a gap visible, and I can quite easily blow air through it. When the thermostat closes, is the pin where the metal disc is attached to supposed to stop the travel, or the metal disc itself?
Should the thermostat be replaced anyway?

Regards Thomas

PorKen

It sounds like it is defective. It should be tightly closed at room temperature.

New ones are inexpensive, so you would do well to replace it.

H2

Thanks, Ken. Good info. I'd like to get a thermostadt that would open wider and allow more coolant to flow through faster....keeping my engine just a tad cooler.

Harvey

PorKen

I installed the 87C thermostat. On the highway, it runs one to two needle widths below the upper white line. (This must have been what was in there when I bought the car, because it ran in the same spot, never higher than the line, even on the dyno.) The front of the head shows 200F with an IR thermometer.

With my intake spacers, the intake is only around 120-130F with 70F air temps!

From what I've been reading, hotter temps make more NOx, but are more efficient, and can produce more power. Newer BMWs have an electronic thermostat which increases the engine temp with low loads, and cooler at high load/full throttle.

I also put in 10W40 Mobil One high mileage for the first time, instead of Rotella 5W40. (Rotella is now more expensive than M1 at WalMartland! M1 - $23.75/5 quarts, Rotella - $20/4 quarts) I swear the engine is quieter, now, at high rpms.

_Thomas_

Hi I installed a new thermostat, Porsche part. no. 928.106.129.17 (got a 'Wahler' 83 °C), together with O-ring 999.701.632.40 and seal 928.106.163.00.
When the motor is warmed up, the cooling water temperature is now also steady 'one to two needle widths below the upper white line'.
If Porsche had fitted the cooling water temperature display with numbers I would have replaced the thermostat a long time ago.

shmark

Interesting. From my testing, mine opens right around 86-87C so I'm wondering if I have the Mercedes thermostat too. Driving at speed, it runs right about the middle of the gauge, climbing to the upper line in stop and go traffic. This is with the a/c running. Now with the outside temp getting cooler, it's running just a little lower than that. My radiator temps run around 70C after it opens with the electric fan on and idling in the driveway. The electric fan comes on just about exactly when the needle gets to the upper line.

hacker-pschorr

Like many things there are two sides to every theory

Todd tries to keep his engine as cool as possible. He fully understands the slight drop in power, but it's a trade off to keep the heads as cool as possible to cut down on detonation. The slight drop in power due to lower engine temp is easily made up and exceeded with a bit more boost and / or timing.
On a N/A car this might not be as much of a concern.

PorKen

This was how my '86.5 ran up till now with the 83C. Near the upper white line, the A/C fan would come on, and the needle would drop.

With the 87C, the t-stat has to work harder to keep the engine hot, because it normally wants to cool very quickly. The needle movement at the top of the range is smaller, and before, it never went more than a needle width above the upper line.

Since when can you compare...well, anything from a FI to NA engine.

IIRC, the Bimmers run less water around the cylinders to keep them warm, and more to the head to combat detonation, and reduce wear on the valve train.

PorKen

It does knock more at full load. It could be that I have too much advance at full load (likely), and reducing the lead may not reduce the power output. Or, I may have to revert to the 83C.

The Beemer e-stat got me thinkin'. I could put a connection between the lower rad hose and the heater hose input into the t-stat housing controlled with a heater valve. At idle and part throttle, the valve would be closed with high manifold vacuum, but at full throttle, the valve would open, bypassing the thermostat, lowering the temps, plus allowing more coolant volume.

H2

If your shark runs just below the top white line in normal driving, where's it at when you run the hell out of it? (on the track, of course). Hard driving creates more heat. My S4 runs between mid line and upper white line, but when I thrash it, it starts moving into the red...and it's overheating. I did some tweeking on it the other week and I've not run it hard since so I don't know if I fixed it or not. When it runs near the upper white line, I get nervous.

I have a 83 Wahl thermo in it and am wondering what other thermo might be better? I understand all that about it not running hot enough for optimal performance but I don't want it to run too hot when taxed. I'm wondering there's a thermo that opens wider, allowing more coolant to cycle?

H2

hacker-pschorr

Hey, just throwing out more info for any boosted guys that read this thread

That would be ideal, I wonder if anyone is looking into a way to do this with a 928 engine.......