How I Solved My Early NA Cooling Problem

[spiffybeard]

My 49,XXX original miles 1983 944 NA has had the problem for some time of running consistently at the 3rd mark on the temperature gauge after warm up. An IR thermometer on the hose going into the head revealed temperatures 90 to 100 C, so the reading on the gauge did appear to be true. The good news is I've solved the problem, and I hope my experience will help someone out.

It may be heresy, but I've come to the conclusion that all cars of this age have lost some of their cooling efficiency. Short of a rebuild, you're not going to get things back to spec. Instead, you have to fiddle around with shortcuts to get back to where you need to be.

The tl;dr version is this...

In my case, the "solution" to my cooling issue was a low temp thermostat with two 2 mm holes drilled at 12 o'clock and 6 o'clock, a matching low temp thermo fan switch, and a later model 6-blade fan setup with one fan disabled. Now she runs consistently between the first mark and the second mark in the middle section. She rarely stays at the second mark unless the AC is running and I'm sitting in traffic.

Here's the longer version...

So how did I end up here? Earlier in the spring, I replaced my timing belt, balance belt, and tensioning rollers as well as the accessory belt for AC and alternator (the '83 has manual steering, so no PS pump belt). Since I was in there, I also replaced the water pump, even though the existing one was upgraded and appeared to be in good shape. Naturally, I replaced the thermostat at this time with a stock 83-degree model.

It didn't seem like my fans were coming on when they should, so I replaced the thermofan switch shortly after. I went with the lower-temp version since I live in Texas and figured what could a little extra airflow hurt? I later learned this probably wasn't the best idea, but you live and learn.

My '83 still has the original radiator top hose (with the red bleeder plug directly in the hose). Despite its age, the hose appears in very good shape, supple with no cracks. I did replace the heater hose coming out of the water pump and the radiator bottom hose as both sustained damage when removing them for the WP replacement. As a side note, I used the cheap URO Parts hoses. I know URO doesn't have a great reputation, but it's a piece of rubber, so how bad can it be?

I drained the cooling system multiple times with a radiator flush and lots of distilled water. I also took the car outside, removed the fan assembly, and doused the radiator and AC condenser with Simple Green, then flushed it from the back with a water hose before painstakingly picking every tiny pebble out of the fins and straightening them with a pick.

And yes, I did thoroughly "burp" the cooling system 20+ times, with the front level, with the front jacked, with a hose from the top hose vent to the overflow tank, with a pressure tester, with the "turkey baster" method, and even with mouth-to-mouth.

Despite all this, I was still running at the 3rd mark on my temperature gauge. As noted earlier, the IR thermometer seemed to confirm the gauge was correct, but I cleaned both the gauge temperature sender and DME sensor with DeOxit to ensure a reliable connection.

Around this time, one of my fans burned out, so I ordered a 6-blade setup from a later model. It was plug and play and moved a lot of air, but I was still at the 3rd line on the gauge. However, I noticed I was typically at the third mark while idling or running at low RPMs. If was over 3k RPMs, I was generally closer to the middle mark on the gauge. Even at highway speeds in 5th gear, the temperature was creeping up.

This told me the problem was not airflow. The problem was coolant flow. When I installed the timing belt, I didn't use a gauge, but I followed Edredas's (YouTube) advice to tighten it so that you can just barely turn the water pump pulley by hand, and when in doubt, go with a little too loose versus a little too tight. I figured I may have erred too much on the loose side, so I retightened the belt.

This resulted in a slight improvement, with the gauge a couple ticks below the 3rd line, but still too far from the middle line for my taste, especially since daytime ambient temperatures were in the mid 60s (F) at the time.

This told me there was a problem with either the thermostat (which seemed unlikely, given it was new) or the radiator. To rule out the radiator, I made the decision to dump my pricey Porsche-brand coolant (interesting side note: My local O'Reilly's now carries Zerex G-40 for half the price) and pull the thermostat.

As another side note, I used a long pair of cheap 90-degree needle nose pliers and sharpened the tips with an angle grinder to remove and reinstall the circlip. It was scary how easy it was. It's also the same cheap tool I used to hold the balance shaft rollers in place when I did that job!

I ran without a thermostat for one warm-up cycle. The gauge never climbed above the first mark. That's a little too cold for my taste, but it did tell me something important: The blockage was NOT in the radiator. The thermostat had to be the problem.

I took the 83-degree thermostat as well as an extra 71-degree thermostat I had on hand and put both in hot water with a temperature probe. This was interesting: At the appointed temperature, both began to open as intended, but as the temperature hit boiling, the low-temp thermostat's "full open" was considerably more than the stock-temp thermostat. I don't know if that's the intended function, but it was certainly the source of my coolant flow issue.

This time, I installed the 71-degree thermostat. I figured the low-temp thermostat should match my low-temp thermo fan switch, and I didn't want to drop the fans again to replace the thermo fan switch. I also had a gut feeling that drilling the holes I mentioned earlier was a good idea from things I had read, and I knew for sure it would help with burping. I put it all back together, filled with Zerex G-40 at 50/50, did a quick burp (and I mean quick - those drilled holes make all the difference), and ran her up to temp.

Now she was still running just a bit too cold with both fans running, just right on the first mark. So I disconnected one fan, and voila! She's now running consistently between the first and middle lines. When we reach summer in Texas, I might plug the other fan back in, but for now, this setup is perfect.

[v2rocket_aka944]

there is no inherent 944 cooling problem.
radiators get clogged even with lowish mileage which can cause issues.

changing the thermostat did not do anything for your supposed issue - thermostat temp is purely a temperature FLOOR. average running temperature (ceiling) is 100% controlled by the fan switch temperature. your old fan switch was working as intended, and now the low temp fan switch will work as intended but turn on at a lower temp.

944 temp gauge sits at that 3rd mark because it's a real gauge and not a "normal" indicator like most cars have. it's perfectly happy sitting at that mark.

[spiffybeard]

Thanks for the reply, but I didn’t change the fan switch. The low temp switch was installed prior to the issue.

I also understand that the gauge is a true gauge, but coolant coming out of the radiator at nearly 100 C while ambient temp is 15 C doesn’t give much wiggle room when ambient hits 38+ C, as it frequently does in Texas.

I’m not necessarily saying my radiator is running at peak capability, but the changes I made are keeping temps sub 90 C under load. I think that’s good in anyone’s book, regardless of how you get there.