A while back I ask about what thermostat to use, early or late thermostat in the new late style water pump. The snap ring distance was for a early water pump.

https://rennlist.com/forums/924-931-...ch-to-use.html

I search around trying to find a answer with no luck. Someone else on Pelican Parts forum ask the question and he didn't get a answer either. A little confused. Well I ordered early and late thermostats, 5 in total from 3 different vendors. I didn't want no trouble. I measured all of them cold and 3 fully open. The answer to this mystery is that all the 944 thermostats are all the same regardless of the part number. The only difference between early or late thermostat part numbers is what rubber band that goes around the thermostat that comes in the box. Thick for the 7mm snap ring distance, thin for the 4.5mm snap ring distance, and a o-ring for which I'm guessing is for some other application. Hopefully this saves some poor soul out there some confusion.

I was also a bit quick to throw Wahler thermostats under the bus. My water pump was the cause of my woes. It wasn't moving any coolant and from looking at it I'm not sure why. Bearings good, impeller and pulley are on the shaft tightly. My best guess is that the pump may have had a very small leak that you can't see but enough to cause the timing belt to slip. I'm kind of doubtful about this. More likely the rubber sealing ring for the by-pass close off was melted and distorted allowing coolant to recirculate around the block???



There's two water pumps Laso makes for 83 944. I used p/n 75200101. It's cheaper than the one that's for the turbo car and it doesn't need the block off either. I installed the pump, gasket dry and torque it to 6 ft lbs, filled the system with coolant and pressure tested it before I installed the rear timing cover. It leaked. I tighten it some more and the leak stop. However one of the 6mm bolt threads in the block let go. God bless the inventor of the Helicoil. I didn't want no more trouble with leaks. I reinstalled the pump with Permarex on the gasket this time and threw the torque wrench away. No leaks. I'll worry about cleaning the gasket off 6 years from now.

In closing the water pump replacement every second timing belt replacement is a fact with these car's. Something which I thought was BS. Not leaking, spins good, it's good to go. To be honest, I've had this car for 5 years now and this is the first time I'm doing the water pump. Please don't flame on this or the double negatives but these cars do have a oddball cooling system. Marc

 

thanks for doing the detective work on this.
i've done a TON of 944 water pump replacements over the years but i always have put the "late" or "turbo style" pumps on, regardless of car's MY.
always wondered which car used that fat seal, since all the pumps i've done (all late type) have used the thinner seal.

re: WP every 2nd belt...luckily they aren't super expensive but it is still fairly frequent.
my Subarus (x2) have 105,000 mile timing belt intervals and some people do those WPs every 2nd belt (210k miles, per pump).

i think the 944's tight TB routing and lack of tension compensation (manual tensioner, even the 87+ spring arm models) is what beats the crap out of the WP bearings.
that, and most 944 folks probably take more than a typical amount of years to get to that 2nd belt interval mileage which dries out the pump bearing seal.

968's with a hydraulic, compensating TB tensioner have 60k mile timing belt intervals, FWIW.

 

Happy to share my finding with the 944 community.

This was driving me nuts. The temperature gauge was reading hot, the upper radiator hose was still cool, but yet the heater was hotter than hell. So I ruled out the water pump and blamed the thermostat. And to add to the confusion the old water pump was a late style pump with the early 4.5 snap ring distance also! I wasn't even sure if the vendors were sending me correct thermostat. With the 80c thermostat installed the gauge stays in the middle now. I still don't understand how the water circulates in these car's. I've never seen so many passages in a water pump before!

 

definitely a lot of recirculation ports, that's why the 944 warms up so fast...

water comes into the pump and bypasses the thermostat from the oil cooler area (small round hole), the heater pipe, the turbo blockoff plate if drilled out, and also down from the cylinder head ("right" side of the WP, triangle shaped port)

 

Thanks Spencer. I was wondering what that small round hole was for.

 

I would like to talk about differences of other brand's of thermostats. Wahler is the standard thermostat for our car's. I've read that people have had runing hot issues after installing a different brand thermostat into their 944's and the smaller opening and reduce flow is blamed for this. I disagree. I believe the cause is the weaker spring for the bypass close off valve. All of the Wahler thermostats I tested takes about 18 lbs of pressure to compress the spring.



​​​​Here's a Stant thermostat that's fits a 944. Only takes about 6 1/2 lbs of pressure to compress the spring:

And why is this important? The water flows towards the thermostat from bypass is port and can force the valve open. So when I said in my first post all 944 thermostats are the same, it's all Wahler 944 thermostats are the same.

 

Good research, Marc! Nice to know! In your hot water testing, did the valve open wider in the Wahler vs the Stant? Probably about the same amount..I would guess. Thanks again!

 

Tiger, they were the same when hot. It was fun trying to get the dial calipers in the 200 degree pot of water.