New waterpump and thermostat - now big header tank pressure? (And higher temp and more fans)

[Mike_Pollock]

Yes - but the reduced pressure from venting the system will allow the coolant to boil at a lower temp - releasing more vapour - thats why it should be cold. Running the engine just ensures that the air trapped anywhere in the system will find its way to the top of the system.

 

[Eldavo]

Mine is the single fan setup hence I'm getting the 2 pin one. It lists the 3 pin as for a 2.7 but when I pulled the plug off the sensor on the back of the fan it is 2 pin only.

 

[DavidL]

ORIGINAL: A9XXC Yes - but the reduced pressure from venting the system will allow the coolant to boil at a lower temp - releasing more vapour - thats why it should be cold. Running the engine just ensures that the air trapped anywhere in the system will find its way to the top of the system.

Mike, Assuming that any volume loss from bleeding is taken up by "excess" fluid in the header tank - obviously not allowing any air to be drawn in - then the system will repressurise when it is sealed up again whether that is immediately or another day. I see what you are saying with regard to boiling point and lower pressure but surely its just temporary? ETA are we talking across purposes here? - I'm banging on about a quick tweak, as Giles did, if you think there is a problem after a coolant change not a complete refill from empty. This you would inevitably do from cold as the engine has no coolant but would warm as the engine needs to be running to allow the air to be removed.

 

[Mike_Pollock]

From a practical point of view, either will work but as someone said earlier its not a good idea to vent a hot engine as it becomes "confused" and trys to spray everywhere! I usually do it hot on the bleed screw very slowly! Yes it is temporary but if you have both cap and bleed screw open at the same time you can draw in air and if you vent it quickley the vapour coming out of the coolant may end up trapped in the very places you have just emptied of air by running the engine. And yes, you need to run the engine just to get a decent fill from empty.

 

[tref]

My experience is that bleedin' 944s' is a pain in the a**! One thing that hasn't been mentioned so far I believe, is to make sure the heater is on when it is bled. Secondly, it is a lot easier to bleed if the car is pointing uphill... It is nigh on imposible on even the gentlest of down-hill slopes. when the engine is cold and empty it takes ages for water to weep through into the block... some people I know reckon on letting the engine warm up, and then the thermostat will open and water will rush in... I don't like that idea, it sounds like overheating engine suddenly cooled, so with the engine cold, I take the bleed screw out, top up the expansion tank. Have a cup of tea, top it up again, have something to eat, top it up again, mow the lawn, top it up again, leave it over night, top it up again, loosely put the bleed screw back in, then fire it up and bleed it. I also top up the expansion tank whilst the bleedscrew is open. Thereafter I will check it regularly, and it is surprising how often I will get further air out. Big airlocks will blast water out of the expansion tank just after the engine is switched off, and the temperature rises because the water pump isn't circulating/cooling. Other things of note: I have found a lot of weak rad caps in the past - the usual give away is a car that won't stay topped up, and old weak thermostats run cold - after changing the thermostat it is usual for the car to run hotter (and do more to the gallon as a result!). Hope this helps, Tref.

 

[robwright]

ORIGINAL: tref My experience is that bleedin' 944s' is a pain in the a**!

Yes they indeed are. This is why when I changed my header cap I converted the old one into my patented pressure bleeding device. I took out the spring and fitted the cap with enough rubber to make a seal and put a PCL airline coupling on it. Incidentally it will also accommodate a foot pump. It is also handy for finding leaks to have the system under pressure. It is anyones to borrow for the price of posting []

 

[tref]

Always meant to make one of those myself, an excellent idea.

 

[DavidL]

You can do similar things with a slightly modified Easibleed. I tried to find the leak on my 21 and promptly blew half the rad core out. At first I thought I'd connected to a tyre at 35 psi but no it was a nice safe 12. Took the rad out the the other half promptly disintegrated!! New rad required.

 

[robwright]

Less than 10 PSI shoild be plenty to do the job.

 

[Sandspider]

Just a quick update. Driven the car several times now, and the coolant level seems stable when cold. I've not bled it again, but will do so in the next few days, and will do it the same way I've always done - with the bleed screw open a tiny bit when hot, engine off, filler cap closed. In the meantime though, my car seems to be running a good bit hotter than it did. I.e. temp gauge usually a couple of mm below the bottom marker for the top 3rd of the gauge, most of the time once it's warmed up. Also, the fans seem to come on a lot more often - not just in traffic, but at 30 / 40mph on an open road on a coolish evening, and even (I think) on the motorway at 75 on another cool evening. Is this to be expected? (When the fans do come on, the temp gauge still stays a couple of mm below the top 3rd marker). I don't think I've every switched the car off since the thermostat change and not had the fans still on after the car is off... I will go and have a wrestle with the search function, but if anyone could tell me if this is the sort of behaviour I should expect now that I've got a new waterpump and thermostat, that would be appreciated. Cheers, Giles

 

[robwright]

Giles in my experience it is unusual for the fans to be on that much. Incidentally how do you know if they are on at motorway speeds? It may well be that now you are running at the correct temperature that the thermostatic switch now also needs changing.

 

[Sandspider]

Thanks Rob I've done a lot of reading, and it looks like my car is now at the top of the usual temp range, and that with the fans on a lot. (As I said, I'm not totally sure if they were on at motorway speeds but I did notice some temp and voltage fluctuations which I assumed was the fans activating). When you say the thermostatic switch, do you mean the temp gauge sensor near the front of the block, in the pic here? [link=http://www.clarks-garage.com/shop-manual/elect-19.htm]http://www.clarks-garage.com/shop-manual/elect-19.htm[/link] (The pic below the two temp gauge pictures). Or is there some other switch (or switches / sensors) that I should be looking at replacing (too)? Cheers.

 

[robwright]

No mate the one that screws into the radiator and controls when your fans switch on and off.

 

[Sandspider]

Ah hah! I thought my temp gauge might be reading too high as the temp gauge sensor is aged & can't cope with new waterpump and thermostat. But you're thinking its the fan control sensor triggering the fans too early / too often? But if that was the case, wouldn't my car be running cooler rather than (appearing) to run hotter? (Indie did say the fans were coming on at about the right temp, but seems hot and lots of fan action to me...) Guess I could always replace them both, if they're not too tricky to do. Cheers for the guidance.

 

[scam75]

I am almost certain it is not bled properly. Try to bleed it when cold and then when just starting to warm, not when fully up to temp! Also lift the front of the car, either on a jack or axle stands or park up a hill. Stuart

 

[robwright]

Giles do you have access to an airline? I will send you my bleeding cap. Then you don't have to worry about what bloody angle the car is at lol []

 

[Sandspider]

Lol! Thanks chaps. I don't have access to an airline, but my drive does slope quite nicely, and I don't think bleeding is the issue. I will check again tonight, and bleed at a wider range of temps. Having said that, when I drove into work today (about 5 miles including gradients, traffic lights & traffic) the fans didn't kick in. They have done on this same journey in the past, though it's not so hot today. I'll give it a bit longer to settle down before I start dismantling more bits of the engine I think!

 

[DavidL]

Giles, I have a compressor which you would be very welcome to use. I claim no bleeding knowledge beyond your own mind!!

 

[Sandspider]

Thats a kind offer David (& Rob), thank you. If it turns out that bleeding is still the problem, I will be in touch. Always happy to meet up and talk 944s anyway []

 

[picopro19k78]

Just spent several (lots) of minutes reading this thread. I have had the same problem of high temp on the gauge as well as the temp warning light lighting. I also (like a fool) opened the ex tank and had several litres of coolant fly out. Quell surprise! After reading alot on the subject I think it is probably bleeding bad also maybe the expansion tank cap. I hve replaced mine and it has made it run cooler and the temp rises slower on the gauge. I think its the bleeding as before my heater matrix was by-passed and so I re-attached it and was very soon aware why it had been by-passed. Previous to this I had changed the coolant and bled the system "to the book" and it used to run only 1/3 to 1/2 up the gauge. After the matrix hell I re-bled it quickly and hasn't been the same since.