Bad water pump? Troubleshoot/diagnosis help

[fasterfaster]

I'd strongly suggest you test the gauge sensor as shown below. This is the last page in out guide and the most accurate way to test it. If the sensor tests ok, then next we can show you how to test the accuracy of the gauge in the car. If they both check out, then at least you can have confidence in the actual temps and are not chasing ghosts. Based on your various comments, at least from this side of the internet screen, it seems like there is still uncertainty about your real temps. One the other hand, spitting up coolant and seeing steam is never good -- so I'd also want to pressure test your cooling system to test for any leaks, and look in the oil cap for any signs of mocha sludge.

temp-sensor-testing.jpg

Super helpful, thanks. I'm ashamed to admit I didn't know about the 944 handbook until you pointed it out in this thread! It'll be a little tough as I don't have a stove or heat source at my shop, which is a 30min drive and $8 bridge toll away from home. But I think I can rig something up with a camp stove so I don't have to do a back and forth.

edit: to answer your other Qs, I have a radiator pressure tester that I used to test and bleed the system, and it held 20psi for over an hour with about a 5ish psi drop, so I feel good about the system sealing.

And nope, no signs of coolant and oil mixing. Both drained recently and looking clear. Nothing frothy at the top of the reservoir or cap.

Have you checked actual temperatures at the sender, radiator inlet/out using an inrfrared temperature gun? These can be had for cheap---the inexpensive ones have limitations and one needs to be aware that different materials and colors can emit varying ranges in the IR spectrum, but one can establish a general trend by carefully tracing the cooling system according to the diagram in the link below.

I felt like I wasn't getting accurate readings off of the rubber hoses - maybe useful to measure a delta, but not an absolute temp. but maybe they actually were much cooler than the crossover? And supposedly IR thermos are not reliable off of reflective metal surfaces, but I was getting numbers that felt pretty close with some trial and error of different angles.

I have seen at my shop a couple of instances of slipping water pump impellers in 944/968 circa 20 years ago, we had a reliable rebuilder for a number of years, but that became less so . . . . have used only new pumps ever since (Laso and Geba brands have been good). But I would first be sure that the cooling system is truly bled. Is there hot from the dash vents with the heater valve open?

Yes, heater is blowing hot, but now that you mention it, I'm realizing that the vent air temp dropped over time. It was piping hot when I first turned it on, and just very warm maybe 10 minutes later... feels like the valve is opening but the water isn't circulating?

As noted above, the last water pump was a rebuild almost 15 years ago so could be of that generation. If I DO get in there, I plan to use a new Laso unit.

IThe advanced move would be an IR camera or attachment for your smartphone, I use this one several times a week at my shop:

That's a great tip, and you're right would be generally useful. I'm always up for an excuse to buy a new tool!

[jeyjey]

... and it held 20psi for over an hour with about a 5ish psi drop, so I feel good about the system sealing.

What pressure cap do you have? It should vent off down to the cap setting more-or-less immediately, but shouldn't lose any pressure at all after that.

[fasterfaster]

... and it held 20psi for over an hour with about a 5ish psi drop, so I feel good about the system sealing.

What pressure cap do you have? It should vent off down to the cap setting more-or-less immediately, but shouldn't lose any pressure at all after that.

the tester replaces the cap, and then i test it at overpressure so that i’m confident it will hold at the specified 15psi

[cda951]

Hi Marc,

Here are a few pics I quickly snapped of my 944S2 engine while idling, using the IR camera attachment mentioned above. I am still figuring out the best way to save and share screen shots---the below are the low-resolution shots saved within the app. If one uses the normal screen shot function of the smart phone, the images are higher-res but show all the menu items within the IR camera app.

I wish I could figure out how to show a scale showing the correlation between the color and temperature, but one can see the general trend by studying the pictures. I also forgot to take a normal reference photo of the engine bay, but I added a couple of black circles to the first pic---the one at the lower right shows the intersection of the metal pipe from the cylinder head coolant outlet (bright yellow) to the upper radiator hose, which demostrates the disparity in IR emissions based on material that you mention. You can see the same at the circle in the lower right corner at intersection of the fat lower radiator hose where it meets the thermostat housing. The metal portion appears to be white hot, but the hose section is demonstrably cooler than the upper hose at the right.

Further proof of coolant flow is shown in the second pic---one can see the hood latch at the bottom center, and can see the top of the radiator through the "windows" to the left and right. The reduction in temperature is clearly demonstrated. The third pic shows the expansion tank and hoses.

You could determine the same with a cheap IR temp gun if you slowly trace the circuit while noting the differences of materials. You can establish a general trend if you do this numerous times and record the readings.

[Dkraven]

From the IR pics it looks like your thermostat isn't opening maybe? I know you just installed a new one, but maybe faulty.

[cda951]

From the IR pics it looks like your thermostat isn't opening maybe? I know you just installed a new one, but maybe faulty.

Thanks for the reply, but I posted these pics in an attempt to help the original poster, my pictured 944S2 engine temps are good .

I can see why you might conclude this from the first pic, as the lower radiator hose inlet appears to be much cooler than the adjacent metal thermostat housing, but this has do to with metal parts having greater IR emissivity than rubber hoses. The proof of coolant flow through the radiator is shown in the second picture (and mentioned in the post above).

The infrared method takes a bit of practice to interpret the system, but with enough study one can establish the general thermal trend. It is quite rare for a thermostat to stick in the closed position, the usual failure mode is they hang open slightly and the engine takes quite a long time to warm up.

[fasterfaster]

Hi Marc,

Here are a few pics I quickly snapped of my 944S2 engine while idling, using the IR camera attachment mentioned above.

this is super helpful thanks! I’ve got one on order - seems a small price to pay for a LOT of troubleshooting info. The good news is my iphone is so old I’m still on a lightning connector, and the compatible cameras are all on clearance, lol

[Dkraven]

From the IR pics it looks like your thermostat isn't opening maybe? I know you just installed a new one, but maybe faulty.

Thanks for the reply, but I posted these pics in an attempt to help the original poster, my pictured 944S2 engine temps are good .

I can see why you might conclude this from the first pic, as the lower radiator hose inlet appears to be much cooler than the adjacent metal thermostat housing, but this has do to with metal parts having greater IR emissivity than rubber hoses. The proof of coolant flow through the radiator is shown in the second picture (and mentioned in the post above).

The infrared method takes a bit of practice to interpret the system, but with enough study one can establish the general thermal trend. It is quite rare for a thermostat to stick in the closed position, the usual failure mode is they hang open slightly and the engine takes quite a long time to warm up.

Hey thanks for the explanation, and sorry for not paying attention to who was posting!