Help and advice needed - 944 coolant issues

Hey All, It's time I held up my hands and seek advice / tips and help with my ongoing 944 coolant issue in my son's car. I changed the radiator temp sensor and as expected, lost enough water to create an air pocket and now need to bleed the system. On a number of occasions, I'd drive around till operating temperature then park it on a very steep hill. Then turn the temp to full heat and turn on the fan (hot air coming out). While idling, remove the stopper from the top of the radiator hose (it's a very early 944) and the radiator cap and wait for the coolant to start circulating and oozing out on it's own (sometimes letting it idle for 20 - 30 mins) ... It seems the only way for me to get coolant out is to blow air through the radiator cap, trying to force the air pocket to let loose. Coolant does come out of the stopper but then stops when I stop. It obviously isn't circulating enough to exit on it's own. I've done a heap of reading and I think I  am doing everything I'm supposed to but am I missing something?? ... When we first got the car, the temp would be on 1/2 and stay there. Now it goes to 3/4 and a bit more so I know changing the sensor has caused this. I don't want him driving it and doing damage so it now just sits in the garage looking sad. Any help / suggestions gratefully accepted. 🙂

I am not an expert by any means but it is possible to navigate a smaller flexible tube to the air pocket and then use "reverse" siphoning effect?

Ronny, I've relied on vigorous bottom hose squeezing with the engine idling and the radiator cap removed but the "modern" way seems to use those special "spill free" oversize funnels that fit snuggly on the radiator that gives plenty of "head". Also, does the thermostat have a air bleed hole that's clear of detritus?

Ok Dreamr I will admit from the outset that I have no idea what is wrong nor am I an expert therefore I'm going to suggest something completely out of the box. Thinking of what I do when I bleed motorcycle brakes I open the bleed nipple and then crack each banjo bolt and keep pumping until a steady flow of brake fluid comes out of each banjo and starting from the top tighten those banjos once free flowing brake fluid comes out finishing with the bleed nipple. Has worked for me every time. Now I know the cooling system is different however in my limited fluid dynamics knowledge I would assume the principle is the same. Crack each hose joint, start car and let fluid flow. What have you got to lose except coolant. The other thing is way back in the early 80's my 924 temperature gauge always showed the same until one day it went up to the red and then within minutes came back to normal only to go back up again. This went on for a few days when I had no choice but to investigate the problem. All it was, was the plug that connects to the thermatic fan switch ( on the fan itself ) over time had broken an internal wire and the fan would switch off depending on how severe a bump I went over and then would switch back on again after another bump. Wasn't regular so I couldn't replicate it. I only found it after playing with the switch and noticed it switched on and off. Wired in a new plug and never did it again. Maybe make sure your fan is working by "jiggling" the switch. No harm in trying. Hope this has given you some ideas.

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Thanks for the suggestion but I don't believe that is a possible solution. It's supposed to be a relatively easy operation .. raise the front of the car so the air pocket travels to the highest point .. turn on the heat so that the water has full circulation through the top and bottom of the radiator ... run till coolant comes out of bleed hole by itself, signalling that full flow is happening and air bubble is gone .. Thanks Pete .. I will try the bottom radiator hose squeeze method next time .. I can't get to the thermostat but I've read about some that drill a small hole in the rim of it to aid in air removal .. Thanks for the suggestions .. this issue is widely documented in the 944 world. It happens when an air pocket forms in the bottom side of the cooling system and gets stuck. The overheating occurs because fluid isn't in every nook and cranny that it's supposed to be in and bypasses areas that need cooling but aren't. It needs to be "burped" ... I've done a ton of research and theoretically it should just work the way I've described. I've heard that some systems just happen and others, like mine, are a PITA ... no idea why the difference.

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Try parking it facing up the slope and do the bleeding etc.  Move it 90 degrees so it's across the slope and do the bleeding.  Move it 90 degrees so it's facing down the slope and do the bleeding. Move it 90 degrees so it's across the slope (facing 180 from the previous across slope) and do the bleeding.

Very crude but you could try. Find a plastic bottle you can upend and tightly fit into the radiator cap seat. Maybe an O ring or the rubber washer off an old cap would seal it. Cut the bottom off it to fill it and open the bleed?

I have no idea about 944's, but would a vacuum coolant filler help with this?  I have recently bought one for doing the 996 but have not yet used it.  You evacuate the entire cooling system so essentially no air remains, then draw the coolant in via atmospheric pressure as required and do not admit any air in the process.  Therefore, there is no air in there to burp out.  Google airlift.  Not sure how it relates to the 944 cooling system but in principle it should eliminate any air-in-the-cooling-system issues.

We have a pretty simple method. With the use of a hand pressure pump that fits on the coolant tank, fill the car with your coolant mix. Start the car with the heater on and let it warm up for a minute, top up if you need to. Put the pressure pump on the coolant tank and add a little pressure. Open the bleed valve until coolant comes out. Remove the pressure pump and replace with the radiator cap now take the car for a 5 minute drive still with the heater on and park on an angle when you return with the nose up. Add the pressure pump one last time, add some pressure and open the bleed valve until coolant comes out. Thats it. Regards Sean

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I think you’re trying to make me dizzy! ... 😅 Appreciate your help and suggestion, but it’s not supposed to be that hard. From the research I’ve done (admittedly it’s not really working though) its supposed to be a lot easier. I have to admit, I’ve never heard of a cooling system being bled this way! ... 😅 Thanks Sean ... I’ll try and get hold of a radiator pressure tester and follow this .. Much appreciated to all that have commented. Its reassuring to know that there are other enthusiasts out there willing to help when needed ... 😀 Ronny ....