Hey guys.
So I bought myself a '84 944 and it was always overheating.
New sensor, new thermostat, new thermofanswitch. Still overheating.
Ive concluded that the water pump was just not moving water. I tested this by removing the thermostat, filling the engine with water and just seeing what came out of the upper water outlet. Barely a trickle. Furthermore I was blowing a little white smoke so I might have warped the head.

Ive got a new water pump
In there. The old one looked pretty corroded, but didn't turn too badly. Could this really be the problem?
been worried about putting this together and setting the belt tension correctly.


I've ordered the tension tool but it hasn't shown up yet.

Are there any 944 techs in Vancouver or the lower mainland that I can hire to show me how to set the tension?

 

No need to worry about the tension so much, just keep a fresh belt on it and tension by hand, recoup some cost and return that tool. Look up 90 degree twist method for the belt. Check out the boss in this video

https://www.youtube.com/watch?v=UvzZ2objumY

Other things to consider with the over heat, partially blocked radiator, internal or external. System not holding pressure due to small cracks in overflow tank or bad cap. Bleeding the system correctly and fully. How was the head and gasket?

 

There's nothing obviously wrong with the head or the gasket.
I took the head in to get tested and they said there was a "slight warp"and resurfaced it.

I don't think the radiator is blocked. I can run a whole bucket of water clean through it.

 

I'm not sure you can judge the effectiveness of the water pump by removing the thermostat with this engine as with others. In the 944 it looks like the thermostat acts as a shunt between the bypass circuit and the circuit with the radiator, such that without it, the water pump impeller just cavitates without moving much coolant anywhere.

Cooling system problems caused by an impeller not moving coolant are extremely rare. I've only known of a few cases...One with a guy I met with an old truck who ran straight water in it for years and years (rusted out), and there are a few cases of water pump designs in some engines using plastic impellers where the impeller would actually slip on the shaft.

Had you tried carefully bleeding the cooling system? Trapped air within the system will cause it to tun hot. You can't just fill these car's up with coolant and go, like 99.9% of other cars on the planet.

 

I am in the sheared composite impeller club but the pump was 22 years old.

For a cooling system to work efficiently it must hold pressure and the coolant needs to be the proper ratio.

Did your fan(s) function properly after installing the new components? Clark's has a good step through on checking the high/low operation.

 

When I bought the car, the fans were always on, even with the key off, even when stone cold.
After installing a new thermofanswitch switch, the fan never turned on.
The car immediately gets hot, and I can manually turn on the fans by turning on the AC, but this doesn't cool things down.
So I've always suspected that water just isn't moving around.
I've tried to bleed the air as best I could. I took out the bleed screw and filled it until it was overflowing. I burped the hoses and everything.

Actually I read something on Clark's garage that mentioned a head gasket failure will push air into the cooling system, which might explain things.

Also: if the belt is slippery, or improperly tensioned, maybe it would fail to drive the water pump?

I'll try the new head gasket and new water pump and try again

 

can you pull the radiator and see what kinda flow you get with a garden hose?

did you replace or inspect the fan relay? ballast resistors may be good since the fans engaged prior to replacing the switch. do not trust a URO brand part to actually work. heat your thermoswitch and check the resistance. I am unsure of the workings of the early cars.

 

The radiator seems ok. I can pour water into the reservoir and it will all flow out through the lower rad hose.

The fans and relays might be all out of whack, but whatever the case may be, I can turn on the AC, which turns on both fans, and this doesn't cool things down at all.

 

If the plug at the fan(s) is flipped, they will turn backwards

 

Also make sure you have the proper radiator cap. Wrong caps are known to wreak havoc.

 

Did you use a oem Wahler brand thermostat? Some other brands have a smaller opening which will cause issues. Verify the thermostat opens & moves enough to close off the bypass or you won't get enough coolant flow thru the rad like Tempest411 posted. Also the thermostat should fit tight in the pump & not wiggle any. There are 2 different size gaskets & a spacer you may need.

 

I think I've discovered the problem!


I was all ready to put the head on and I tried to turn. The water pump by hand. It would not turn.
I know I torqued this to spec, and it would only turned when I loosened the bolts.

I took the pump off and the impeller seat looks a bit scored


You can see its oddly formed from about 1 o'clock to about 6 o'clock.

So here's what I think happened: an old water pump bearing went bad, the tension from the belt pressed the impeller hard into the block and distorted the seat. Now the water pump can't turn easily and impedes water flow.

That's my guess anyways.

How am I going to make this flat again?

 

Bummer. They do put up a struggle.

Compare the depth of the impeller on both pumps. If the new one doesn't have the impeller seated on the shaft all the way, return it. If they have the same deck, I would be tempted to make a gasket out of thicker material and go with it.

 

Was the pump a rebuild from a local auto parts store? I have seen them sell 2.7/3.0 pumps as 2.5s. The pumps are identical except for the size of the impeller. A lot of the big rebuilder outfits have no idea there's a difference.The 2.7/3.0 pumps have larger diameter impellers that will do exactly as you've found-hit the block. I have heard a few people say you can increase the capacity of the cooling system of a 2.5 powered car by clearancing the block for the later large-impeller pump. But as this isn't done very much, I assume it's not that big of a deal...

 

It's also a good way to ruin a block. The pumps rely on a specific and rather tight clearance to the block to generate flow. If you open it up too much you'll dramatically effect the pump's efficiency in a very bad way.






To clarify, a 3L pump on a 2.5 block will strike the block at the cutwater, NOT in the area your image shows. It appears from the looks of things that you got a faulty pump; one where the impeller was not pressed onto the shaft all the way and is instead a mm or two proud. It's possible the impeller or shaft is also slightly bent; that area of the block that is marred is a flat surface so if the impeller were straight and simply not seated onto the shaft far enough, I would expect to see a circular mark all the way around the area, the same diameter as the impeller.