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Changing a 944 Thermostat

Pelican Technical Article:

Changing a 944 Thermostat

Michael Van Bibber


3-4 hours






Large flathead screwdriver, metric socket set, snap ring pliers with 90-degree bend, water supply, drip pans, many shop rags, gloves, metal polish, degreaser, floor jack, jack stands, wheel chocks, safety glasses, torque wrench, brass wire brush,

Applicable Models:

Porsche 924 (1977-82)
Porsche 924 Turbo (1980-82)
Porsche 944 (1983-89)
Porsche 944 S2 (1989-91)
Porsche 944 Turbo (1986-89)
Porsche 944S (1987-88)
Porsche 968 (1992-95)

Parts Required:

54mm thermostat in 160 degrees, 180 degrees or 190 degrees, new seals, O-rings, a spacer (optional), bottles of radiator flush (2), radiator hoses (as needed), coolant

Performance Gain:

A clean and properly functioning cooling system for your 944's engine

Complementary Modification:

Replace the water pump

If you car is running a little hotter than you think it should, perhaps you need a new thermostat. Here in Florida, high outside temperatures combined with stop-and-go traffic can raise your engine temperature up to the 3/4 mark pretty quickly. My solution was to put a 160-degree thermostat in the car, and to flush out the cooling system thoroughly. Optionally, on the series 1 944s, you can install a lower temperature thermoswitch. Though this article was written based on a 944 NA, the same principles apply to a 924S/944S/S2/951/968.

Though this would seem like a simple procedure, removing the thermostat can be an exercise in frustration. By virtue of its location and how it is mounted, it requires special tools and/or some creative engineering to remove.

Naturally, once you start this procedure, inspect all of the hoses and clamps for wear, replace as necessary.

Warning/Disclaimer:You will be working on a hot engine, and draining hot fluids out of the car, there is the potential to burn yourself, be careful. Also, consult your local regulations regarding disposal of anti-freeze.

Tools Needed:

  • Large flat head screwdriver
  • Metric sockets
  • Snap Ring Pliers - get the ones that have a 90 degree bend with tips that are fairly thick OR Miniature round nose pliers - straight or 90 degree bend  OR Awl
  • New Thermostat (NAPA carries a 160, 180 and 190 degree version) It doesn't have to be a Porsche thermostat, just one that is 54 MM in diameter.
  • New seals, O-Rings and optionally, a Spacer
  • Radiator hoses (As needed)
  • 2 bottles of radiator flush
  • New Coolant - Coolant that is approved for "DEX-COOL" works well.
  • Water Supply
  • Drip pans and a lot of rags (I used 3 large drip pans).
  • Gloves
  • Metal Polish (Optional)
  • Degreaser (Optional)


1. Run the car and turn on the heat, once you start getting warm air, shut the car off.

2. Jack up the car and support it on jackstands, if you have one, remove the belly pan.

3. Let the car cool for about 10 minutes.

4. Place a drip pan under the radiator drain and one right in front of the crossmember.

5. Unscrew the radiator drain; be prepared for a rush of warm coolant.

6. Remove the cap from the expansion tank - the coolant will really squirt out now. Allow the system to drain as much as possible.

7. On the passenger side of the car, remove the lower radiator to water pump hose, be prepared for yet another rush of warm coolant. If you have timed this right, the thermostat will still be open, allowing the engine block to drain. There is a bolt to drain coolant out of the block located on the passenger side of the engine. However, this bolt can be difficult to get at, and in many cases, it has corroded and fused to the block.

8. Inspect this hose for excessive wear. If your car is equipped with power steering, any seepage or small leaks will have splashed power steering fluid on this hose, causing it to soften/swell. My hose actually had a flat spot from where it was resting against the inner fender. This, coupled with an old PS fluid leak, had softened the hose to the point where it was sticky. If this area is greasy on your car, I recommend thoroughly cleaning and degreasing this area before you continue - your hoses will thank you.

OPTIONAL: Disconnect the upper radiator to engine hose at the radiator. Take a garden hose and hold it in the lower radiator outlet and turn on the water. This back-flushes the radiator and should remove any clogs you may have.

9. Optional: If the water pump/radiator hose connection has a bunch of crud on the outside, you can remove it with a rag and some of the radiator flush. Use a brass wire brush if the crud is really caked on.

10. Now it is time to remove the thermostat. It is held in by a 55mm x 2mm snap ring. As you can tell by looking, you do not have a lot of room to work. This ring is much easier to remove on the newer style water pumps, but can be an absolute nightmare on the older pumps (because it is in there deeper). Find the holes in the ring and work it out the best you can, hopefully without damaging the ring or your water pump. If you can't get at it easily, you can try inserting an awl in one of the holes and spinning the ring into a better position. Some mail order catalogs offer a "Water Pump Helper" Tool to get the ring out - it runs about $25.

11. Once you get the ring out, pull the thermostat and any o-rings, seals, and spacing rings that may be in there, making note of which order they went in. Be prepared for yet another rush of coolant.

OPTIONAL: Now that the thermostat is out, you can take your garden hose and back flush the block. Do this by connecting the garden hose to the engine head to upper radiator hose. Any loose debris will shoot out of the water pump.

12. At this point, I wiped the thermostat housing down with a rag soaked in radiator flush, then polished it with metal polish, making sure to remove all traces of polish when I was done. Since I was reusing the spacer and the snap ring, I cleaned and polished them as well. This removed a lot of crud, making the new thermostat seat securely and made the snap ring easier to install.

13. In the classic Haynes style, installation of the thermostat is the reverse of removal.

14. Reconnect the hose, clamping everything down tight and replace the radiator drain plug.

15. Time to flush the system. Empty the bottles of radiator flush into the expansion tank, followed by water - keep filling the tank to just above the maximum mark - the water will be sucked back down as you run the engine.

16. Since the block no longer has coolant in it, you have two choices to fill the system.
A. Run the engine and continue adding water to the expansion tank until the system is full, bleeding it in the process. - This can be an exceptional pain.

B. Disconnect the hose at the top of the motor, and filling the block with water, then pouring water down the hose and into the radiator, filling it up as much as possible. If you backflushed the system, this hose should be disconnected already. This ensures the block is full and reduces the amount of time you have to bleed the system.

17. Reconnect all hoses and start up the engine, and let it run for 10 - 15 minutes with the heat on, bleeding the air out of the system and adding additional water as necessary. Keep an eye on the engine temperature, since you are running plain water, you cannot let the engine get too hot or the water will boil, causing all sorts of problems.

18. After the engine has cooled for a bit, drain the water and radiator flush. You can speed this up by disconnecting the radiator to water pump hose at the radiator - BE CAREFUL, the water will be HOT.

19. After the system is drained and cooled, repeat steps 15 - 18 with plain water.

20. Repeat steps 15 - 18 again, this time with coolant and water. Bleed the system completely.

21. Check for leaks over the next couple of days, topping off coolant as necessary. To be safe, you should bleed the system every day for a few days afterwards to ensure trapped air bubbles are worked out.

Bleeding Tips:
Once the system is full of coolant, loosen the bleeding screw slightly. You should see coolant bubbling from under the screw. As the system forces air out of the system, you can feel the head to radiator hose heat up. After the hose is a uniform temperature squeeze it a few times, this creates a small backpressure wave through the system, helping to force trapped air bubbles loose. Once you have a steady stream of coolant oozing out of the bleeder screw, tighten it down, you are finished.

Michael Van Bibber (AFJuvat)

Comments and Suggestions:
Andy Comments: I have a 84' 944, I bought a Wahler thermostat that came with 2 O-rings, one larger, round and thicker. The other one is smaller, square and appears to fit on top of the thermostat. What is order of placing the O-rings, thermostat and snap ring. The old rings was badly deteriorated and missing, unable to tell where it belonged. I have the original water pump.
April 27, 2017
  Followup from the Pelican Staff: I think it takes only one sealing O-ring. On the top of the t-stat. Choose the right O-ring for your vehicle. GOing by memory. If old was damaged, going to be hard to tell. To be sure, Give our parts specialists a call at 1-888-280-7799
- Nick at Pelican Parts
Gene Comments: 1986 944 non-turbo. The radiator fans keep running after the engine is shut off but the temperature guage doesn’t register as being “HOT”. Where should I start troubleshooting?
May 24, 2016
  Followup from the Pelican Staff: Check if the fan relay is always being commanded on or if it is stuck. You will need to locate the wiring for your vehicle. - Nick at Pelican Parts  
Matt Comments: I'm replacing the thermostat on my 1980 924 turbo. I'm confused about the O-ring placement. Does the O-ring get placed above the thermostat connected to the outlet oe is is placed under the thermostat where the housing is that connects to the head?
April 27, 2016
  Followup from the Pelican Staff: The O-ring goes on top of the thermostat, then the housing goes over it. Install thermostat, then O-ring. Going by memory, but I think the newer models had an O-ring that went around the thermostat, old models it was on top of the thermostat. - Nick at Pelican Parts  
jon Comments: Hi, I'm planning on replacing my thermostat but my car doesn't blow any heat. So do I just leave it running for a few minutes before I start draining the coolant?
February 29, 2016
  Followup from the Pelican Staff: No. Do not drain the coolant until the engine is cold. - Nick at Pelican Parts  
Jan Comments: Is changing the thermostat in the 924 turbo the same as the 1988 911 Porsche can I Gt a repair book for the 1981 turbo carrera t? If so please let e know where to mail for it and the best and cheapest place for parts.
November 7, 2015
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
kastirli Comments: I have a 1987 944 Base and have had numerous overheating issues. I found the best change was to use the high flow Wahler thermostat. Look at the size of the hole in the middle compared to others 180 deg was fine on very hot days.
The other thing I want to share regarding balancing shafts. Don't bother with them. There is only a hardly noticeable vibration at 1800rpm and 3600rpm, but to me this goes along with a sports car. I have run the last 100,000mls with this high pitch whining balancing belt removed. Makes working on the engine a whole lot easier!!!
September 2, 2015
  Followup from the Pelican Staff: Thanks for sharing your experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
Joe Comments: Hello there! Could you help with a diagram or instructions on how to remove the dashboard on a 1987 Porsche 924S? I am going to re upholstery it. Thx for your help!
April 5, 2015
  Followup from the Pelican Staff: We don't currently have that tech article. If we get a chance to perform the procedure, we will be sure to document it.

I would grab a repair manual. It will have the procedure, special tools and torque specs.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
Joe Comments: Need some wisdom please! Planing on installing the 160 deg thermostat on my 87 924s. Gets very hot in Orlando Florida and my question is, will the second high speed fan come on at all to cool the car still? Would you recommend replacing the thermostat switch also? The fan comes on but when it gets very close at times right before the red mark. I discovered that there is a faulty connection on the fan itself. Any suggestions greatly appreciated! Joe
April 2, 2015
  Followup from the Pelican Staff: If the fan comes on too late, the sensor may be faulty. Try repairing the faulty connection you found and replacing the fan switch. - Nick at Pelican Parts  
Joe Comments: If you use a 160 deg thermostat on a 1987 Porsche 924s, do you have to use a lower temp thermostat switch to turn fans on???
February 14, 2015
  Followup from the Pelican Staff: No, the fan is designed to operate at a certain temp. It will still run at the hot temp it should. - Nick at Pelican Parts  
Corky Comments: Remarkable;this is part of the info I need for my 87 944s.Overheating as I took fan fuses out,cause it kept running after shutting down;ran down battery constantly. Shop said no idea how to change thermostat. Another wants a fortune and said if he could find parts.Looked online and you 2 hours later made my day, without having to spend a dime unproductively. Thanks again, you are appreciated. If you had pictures you would be perfect.

October 3, 2013
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
jerrymoran Comments: i have a 1984 944 porsche, do i have to drop the gas tank to empty the bad gas?
also, where is the fuel pump located? is it easy to replace or difficult? any comments? there are two sensors located upfront, where are they located and what are they called? thanks for your help
February 13, 2013
  Followup from the Pelican Staff: The fuel pump is easy to get to. it is in front of the right rear tire. I would remove the fuel tank and have it cleaned. If you would prefer not to, you'll have to siphon the fuel out and hope you get it all. - Nick at Pelican Parts  
Dan Comments: check the vaccume tank, no vaccume, no heat control.
May 3, 2012
  Followup from the Pelican Staff: Check the vacuum line to the tank. It may be plugged or broken. - Nick at Pelican Parts  
Kesper Comments: I have 924s 1986 no power steering .
Mine stuck I can not undo and removed! Any suggestions how to remove?
March 6, 2012
  Followup from the Pelican Staff: The pump is stuck? You will have to replace it. - Nick at Pelican Parts  
Bill Comments: To vvrjim:
I had a similar situation and discovered the problem when I took the dashboard off to cover it - one of the plastic clip connectors for the cabin climate control broke. The one that I needed to replace could be done without removing the dash, but the other - I don't know. The 944 climate control is nice and does a great job when it works properly.
June 26, 2011
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
hr Comments: The instructions and prep. suggestions for replacing my '87 944 thermostat much appreciated by me. You're right-this was a 10 level frustration job. I'll sell the car before I ever do it again.

June 25, 2010
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help, sorry it was so frustrating. The woes of working on your own car I guess.
- Nick at Pelican Parts
motormach Comments: hi all ive got my self 944s got to change cam and balance belts is it hard to do and can i buy workshop manual on the 16v engine any wear look farword to your comments
thanks steve
April 23, 2010
  Followup from the Pelican Staff: Hi there. I'll have sales contact you for pricing on the manual set. - Wayne at Pelican Parts

Hi Steve, short of spending several hundred dollars on the factory workshop manuals (although they are far and away the best manuals), all we have available is the Haynes book. It's item number BK-112019AM and costs $20.95 + shipping.
Martin Comments: If you don't have a ring compression tool, do the following:

Carefully compress the ring in a vise so that the open ends are touching. With thin wire, wire the holes together and slowly open the vice. Make sure that the open ends do not go anywhere. Properly insert the thermostat and seat the ring in its grove. With a good set of wire cutters, cut the wire that holds the ring together and slip out the cut wire.
Make sure that you do not leave any bits of cut wire in housing.
March 23, 2010
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
March 10, 2010
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
vvrjim Comments: On my 16,000 mile 87 944, the heater climate control system? blows hotter than the temp control switch says, and it pulsates, blowing hot air, then cool air. It only does it at lower temp settings on the control swithch. So far, I have replaced the heater control valve, bled the water per OM, checked the lever by the driver's foot, and cleaned the air intake on the inside, all to no avail. My next move is replacing the thermostat. Any ideas? Thanks!!!!
February 28, 2010
  Followup from the Pelican Staff: I wonder if there is a problem with the blend door. If it is cycling, causing the temperature change. I would look into that.- Nick at Pelican Parts  
chili951 Comments: The thermostat seal inner or the inner seal thermostat housing. where the inner seal goes in the housing and then the thermostat follows. I'm tring to replace inner seal, it seams that the esal is the same dia. as the hole. 86 944 turbo
July 13, 2009
  Followup from the Pelican Staff: It sounds like you are looking for replacement seals. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts

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Page last updated: Mon 1/22/2018 02:22:02 AM