944 Cooling System

Leaking Water and Even Overheating!

The info below is a typical 944 situation. This particular effort was on a 944 turbo but the basic approach and fix are very similar for the 944 or 968.


My new purchase came with no service records so, I needed to get a early look at the condition of the belts because as we all know, a broken belt means a lot of work and big $$$. 

Changing the belts and rollers was on my list but I wanted to be sure the water pump was OK too.  It would be aggravating to swap out all the belts/rollers only to have to go back in again to do the water pump. So.... checking the water pump starts with checking the condition of the water pump pulley. Generally, I look for evidence that the belt is slipping on the pulley surface.  This "evidence" is pretty unscientific and, in my case, inconclusive.  I could feel a little lateral play on the water pump pulley and that is usually a bad sign. I had also  heard a chirping sound with the engine running which I imagined might be a roller with a dry bearing. Other stuff included a hint of a water leak and the usual oil film over the lower part of the engine - maybe a little worse than usual.  

The previous owner told me too that he'd had some concern for the cooling system but hoped that it was only a defective expansion tank cap. On 944s, cooling system problems almost always end up being related to the water pump - overly tight cam belts cause them to fail pretty frequently.  I'm still dreaming at this stage though, hoping maybe it is just some leaky hoses. There are so many connections, especially on the turbo cars, that leaks are pretty common too.

To find a leak, its easiest to put pressure on the cooling system and look for the drips.  To do this I rented a tester and sure enough found a few leaks.    

Side note: the tester seen here is a Stant tester, a very good piece of equipment that can be "borrowed" from Autozone. I was so impressed that I kept mine ($80).

One side note about the big clamp (;ower area in "Leak Number 1."  Be sure to make note the orientation of this large hose clamp - with the screw nearest the center of the car. This is the correct way to have it installed. Its more trouble to get it in this position because the clamp can't be secured until after the fans are in but there is a real upside. If it is turned around so the screw is out (nearer the driver's fender) that screw will be very close to frame rail, and will contact that rail during some driving "events." When that happens the vibrations are transferred through the clamp and to the radiator neck. This contributes to failures of the radiator. This is a very common problem on 944s and is avoidable.  


The 4th leak is coming from the cooling fan switch - which cannot be accessed without removing the cooling fans; which cannot be accessed without removing the oil cooler, which cannot be accessed....... You can begin to see where this is going.

The 5th leak is the worst because I couldn't confirm where it was coming from. I drained the radiator, removed the belts, tensioner's & rear belt cover and then re-attached radiator hoses. I could then re-pressurize the cooling system and confirm that the last leak was from the the water pump. You can see too, that I have a few oil leak issues so I'm starting to see an all-out front reseal and water pump job in my future. And so it begins.

To get the water pump removed, we have to remove the rear belt cover, the balance shaft gears (aka cogs) as well as the gears on the crankshaft. All of those are easy except the crankshaft gear. It is held in place by a large bolt that is torqued to ~160 in lbs. This, too, is do-able if you have the right tool. 

To loosen the crankshaft bolt means somehow preventing the crank from turning. You might reason that you could put the car in gear and set the parking brake to hold the engine. True enough, this can be done on some engines, but, unfortunately, the Porsche 944 is not one of them - there is just not enough clutch friction to hold the crank from turning. Attempting this can even result in damaging the rubber centered clutch that is used on the 944NA. The most common solution is to disconnect battery, remove the starter and, in its place, insert a flywheel lock. 

Before locking the crankshaft, lets look down the road a little. Pulling those belts, gears and pulleys  means we will have to get the engine back in time so lets look at the timing marks.  Generally, I get the PS belt and AC belt off. Then pull both the upper belt cover and the cam gear cover. Then, I can remove the lower front belt cover also. Now the belts are exposed. First take a peek at the lower balance belt cog to find the alignment tab and the small v-cut in the cog itself. Note: the marks are probably not in alignment yet - thats coming. The pics below show them in alignment.


Next the upper balance belt cog. 

The cam - note the distributor cap and aluminum gear cover is removed for this pic.


And finally the crank shaft - it has two marks; either will work.


Before you remove the belts or install the lock, you might observe the relative position of the cam and balance gears.  If you're not familiar with the various timing marks then now is the time to get comfortable with them, so you will know how to get the engine back "in-time."  

So once I get the upper front belt cover off, and the distributor cap/cam gear cover off; I rotate the crank (face the front of the engine and rotate clockwise until I can see the cam gear marks lines up (see pic above). Next, I confirm the crank mark is at TDC; meaning the crank marks are in alignment and therefore the crank/number 1 piston is at Top Dead Center. (either crank mark will work for this but I prefer the one at the bottom of the clutch housing (sometimes called a bell-housing). And last, I should be able to look at each of the two sets of marks on the upper and lower balance belt cogs) and verify that the counter-rotating balance shafts are in alignment with cam/crank TDC.  Side note: its a little surprising how often I find the balance shafts are not in alignment. If not aligned - you will witness a engine vibration at around 3000 RPM but there will probably not be any damage to the engine from this problem. 

As a general exercise, put the transmission in neutral and rotate the crank clockwise and observe how all the marks come back into alignment after two full revolutions (720 degrees) of the crank. This is the part that you want to be comfortable with because this will be the "test" that you want to do after installing a new waterpump/and or belts as a last step before putting the belt covers back on.

So now, we' re read to install the flywheel lock. I like to have the crank locked at TDC - its just an assurance that the lower part of the engine is not moving. And its easy too since the crank marks are available at the bottom of the engine, right near the starter. 

So now we're ready to remove the cam and balance belts, On all 944, you would just loosen the balance belt tensioner cog to then remove the balance shafts belt. The cam belt varies by model year and if you have the 87 and later 944, then you will loosen the cam belt by loosening the adjustable spring tensioner. Hint: loosen bolts A&B; use a combo pin wrench or a small pin wrench to rotate the spring tensioner and thereby loosen the belt (the spring tensioner will rotate about 10 degrees). Hold the spring tensioner in that position (retracted) and re-tighten the bolts A&B. Now the remaining two bolts on the spring tensioner can be removed and the spring tensioner can be separated from the engine.  This will save some headaches with trying to get the spring tensioner off and back on the engine). The cam belt can be removed at this time.


Now if I were only replacing the belts, I would begin re-assembly at this point.

If you need to go deeper (like I did for my water pump) we're finally ready to pull the crankshaft bolt (power steering pulley, AC pulley, balance belt cog etc). 

With the belts & tensioner out of the way and the flywheel locked , I can move on to removing the crankshaft bolt. Some people try the chin-up method but I've never had luck with that approach; the shoe-on-3 foot breaker bar works though unless you mange to break the socket or breaker bar. I'm doing this with a 1/2" drive socket but 3/4" drive tools are a nice-to-have here. Note even though the tightening torque is around 160 foot/pounds, it may a need more torque than that to get this bolt loose as Porsche used sealant on the threads (I think to help with oil leaks). With the bolt out, the power steering pulley will fall off the end of the crank.

Here is a good point to look over your power steering pulley, many have been assemble incorrectly. Take special care when reinstalling this to get it centered.

The lower balance belt gear will probably be stuck and you may be tempted to pry it off with some sort of lever. This might work but you risk damage to the surrounding components. Here I'm using a typical gear puller and you can see that it just barely clears the radiator. 

With the crank gears out of the way, I can remove the rear belt cover and finally get a good look at the crusty old water pump.

One note concerning the water pump - one of the nightmares that can occur when changing a water  pump is breaking of one of the small mounting studs or bolts. These are often  weakened by corrosion. Apply heat to soften the thread locker and remove them carefully. Many vendors (and hardware stores) sell metric studs, very few sell the correctly hardened and treated ones. As far as I know, the Porsche originals are the best. 

This is the time when you need to decide if you're going to replace the engine seals. If you're interested in how to do that, see our page "944 Front Engine Seals", else continue here to prepare the new pump and start re-assembly.

Preparing the New Pump

One of my leaks (number 3) was due to the small nylon fitting that houses the turbo-charger's thermostat (yes the turbocharger has it's own thermostat). The fitting can also serve as a block-off if you have a turbo prepared water pump and want to use it on a non-turbo car. To prepare the fitting for use in my 951, I had to start with drilling out the inner wall. 

You can see the general position of the two thermostats, I would have replaced both of them with new but somehow I got an 80 degree main thermostat and an 83 degree turbo thermostat. I'm thinking they ought to both be the same, so I'll use my original. By the way, my new pump is a rebuilt unit from Zim's and comes with a gasket and an inner thermostat seal. Note: all of the water pumps shown here are updated pumps, for more info on this see our "944 Updated Waterpump?" page.

Note: before installing a new thermostat, check the condition of the inner seal, see above. These generally don't fail. There are two seals, an inner one, (seen above) and an outer one that situates next to the t-stat. For that outer seal, there are two possible versions. I believe the earlier cars (prior to 87) got a pump that uses a bigger seal. Getting that seal, t-stat and snap-ring in place can be a tight fit and topic of some frustration. The later pump/t-stat arrangement uses a seal that lips-over the outer edge of the t-stat. It is easier to get installed.

It is of course best to get the correct seal. I can report though that I have seen the small lip-over seal used in pumps where it was not correct without a problem noted. You will know that you have this situation if, when you install your t-stat, it is a little loose and can be rotated. With the correct seal, it will be snug - and perhaps provide better control of water temps.

One last note about the snap-ring. Snap-rings are wonderful but they are also a pain, especially with the bigger ones. This is compounded even further if they are located in a difficult-to-get-at location, like, say an installed water pump. When you install the snap ring to capture the thermostat, position the snap ring opening to 12 o'clock. This will be helpful if you should later need to change the thermostat - without removing the pump.


On the water-pump...Some people use a gasket sealer, some don't. I tried it once with no sealant and promptly developed a small leak. Since then I've always used the sealant. The down side is that it is extra work to clean the old sealant from the front of the engine.  You may be tempted to dig out an old scraper but beware, this aluminum is soft and scars easily. Both mating surfaces get a light application of acetone to insure sealant bonding. 

All that is left  is to place the pump on the engine and carefully tighten up the fasteners. Again, be careful not to over-torque. 

Final note: when I got everything back in place and refilled the coolant, I went back to the pressure tester to make sure I had all of the leaks. Everything seemed fine, so I just left the pressure tester connected with pressure applied. About an hour later I noticed that I had yet another leak. And, it seemed to be coming from the area of the turbo charger. I thought sure I was going to have to pull the intake and isolate the leak. But then I heard a faint hissing, thankfully, it was just the bleed screw that was leaking.

New reservoir tanks are about $260 for the turbo cars (they have doubled in the last ten years). The turbo tank is NOT the same as the NA tank.

One Last Assembly Note:

If you should manage to leave a loose bolt inside of the belt covers, disaster can occur.
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