Back in a 944

[murv69]

Hi all

Well my last ownership of a porsche 944 was very brief but am glad to say I a now a new owner of a 1989 2.7 in guards red. The car itself bodywise is in very good condition and the engine is good, it has a few electrical problems that I have managed to fix but will no doubt be looking at a bit of advice of a few other things.
I know it has been cold over the last few days but one thing that is bugging me is that the car runs very cool, the tempereture guage rarley gets above cold, it does if in traffic & the fan cuts in ok.
If I turn the heater on its not what I would call hot but if I hit the defroster button its very warm. I am thinking that the thermostat may be stuck open. Is there anything I need to be careful of when changing a thermostat in a 944, I have changed many in the past on other makes of cars but thought I would ask .

I will get it polished up & a few snaps taken over the weekend and look forward to chatting a lot more

Cheers Simon

 

[Riverside]

If the heater air is hot when you put the windscreen demister on then the problem can't be with your coolant or thermostat. I had pretty much exactly the same symptoms on mine when I first got it & changed the thermostat. It's a right pain to do and it made no difference at all. The heater's automatic temperature control works by measuring the cabin temp, air temp at the heater inlet (under the bonnet) and inside the air distribution chamber (ie after the heater matrix has warmed the air). Any of these three thermistors may have failed, and they could fail open or closed. There is a diagnostic checklist to follow in the service manual (downloadable from various places, try [link=http://www.promax.com]www.promax.com[/link]), you'll need a multimeter. If one of the thermistors has failed you can replace them new from Porsche for about £11,000 each (approx) or from any electronics store for about 4p & however much a soldering iron costs []. I know almost nothing about electronics & fixed mine without any drama, it still works fine 3 years on. hth

 

[Fen]

I'd still say change the 'stat. I have found most cars benefit from it, my 944s in particular. The gauge should sit pretty steady a little below the middle of the scale at all times with a working 'stat, the exception being in traffic where it will climb to the marking just past centre before the fan brings it back down again. If it isn't doing that then the 'stat isn't working correctly. I agree in the main with the above however, as you should be able to get air as hot on the hot setting as you do with the demist setting as clearly pushing the demist button can't make the coolant warmer. Basically I think you have 2 problems.

 

[homesea]

It sounds like you dont have a stat in or it could of stuck. Nasty people have been none to remove stats to hide overheating problems. But they are a bit tricky to change so its not like it is a 5 min bodge. Once the car is up to temp then you should have hot air in the car, if not then you have another problem. Could it be that the stat is stuck so the car is taking a long time to heat up so it's taking even longer to heat air up from the heater matrix?? As to the heating I been told to remove the sensor behind the round grill thing in the dash and clean it out.

 

[Fen]

If it has the numbers on the heater knob then there could be a multitude of causes for it not blowing hot. Besides the thermistors mentioned above Tom is right about the little round vent. There is a hose behind it leading to a fan above the glovebox. The hose needs to be connected both ends and the fan needs to have all the lint that accumulates on it removed. Also next to the glove box (it's maybe worth taking it out to check, but pull the fuse for the light first to save blowing it) there should be some linkage rods with plastic clips connecting them together. If any of the clips break you get weird temperature behaviour. I don't think that is the issue here, but you never know. In a completely different area the vacuum hose that connects inside the cold-air chamber in the scuttle needs to be connected, not leaking and not clamped in the seam of the chamber as the one in my cab was. It's a relatively complex heater control system and I confess I don't know exactly how it actually works beyond it measures cabin temperature via the little grill and maintains it by blending ambient air (all the addition of air-con does different is cool the ambient air below ambient) with heated air, the mixing being done by manipulating flaps both electrically and under vacuum. It is very, very good when it's working properly. After I discovered (accidentally) that the vacuum hose in the cold air chamber of my cab was crushed and fixed it the heater was nothing short of brilliant; it would maintain a constant temperature hood up or down even when alternating between motorway speeds and rush-hour crawl. I don't know how much of the above applies if you have the red/blue markings on the temperature knob, but I suspect most of it is no longer relevant, possibly only the clips.

 

[Diver944]

Hi Simon and welcome back [] The guys are right about the sensors probably being the cause of gentle heat unless the defrost button is pressed. I would check the sensor in the engine bay. It is directly in line with the steering wheel at the bottom of the windscreen glass, and by the grille for the heater intake. This senses the outside air temperature and when it fails the system thinks it's hot outside so doesn't mix enough warm air from the heater matrix. Mine failed about 8 years ago and was around a tenner from the dealer back then

 

[murv69]

Cheers guys A lot to think about there I will have a look at these, I will probably try the stat too as I drove it home 95 miles all motorway and the tempereture dial hardly moved, although if you stop it does creep up & the fan cuts in. Didnt get around to taking any pics as too busy today plus really does need a clean again Cheers again Simon

 

[peanut]

I would have to offer a word of caution about changing the stat. They can be an absolute barsteward to change . Bleeding the air out of the system can be a nightmare . My Indie had to resort to raising a temporary supply header tank 2 metres above the car after hours of bleeding the system unsucessfully.The reason is the heater control valve is shut when the engine isn't running because it is controlled by vacumn therefore an airlock is created in the heater circuit There are 2x thermostats available in the UK with different temperature settings one will leave your gauge on the first marker at normal running the other stat will leave your guage reading just under half. You need to check before ordering My gauge never goes above cold yet the heat is like a blast furnace. I would check you haven't got some air in the heater system and check that the thermostatic heater valve is operating properly. They frequently get sticky and don't open properly Have a look in the Clarkes garage site under 'Garage shop manual' under 'heater' there is an excellent troubleshooting guide with full diagrams. Blimey its complicated [link=http://www.clarks-garage.com/]http://www.clarks-garage.com/[/link]