Pinpointing Overheating source

[Captain_Birdseye]

Hi, if anyone has the time to read I'd really like your opinions. I have done some digging in the wiki, other peoples posts which have been useful and google too. I have a weird leak from my coolant tank but theres a few twists to the story.

Background: (don't have to read).
-Recently had a leaking top hose replaced and the engine had got extremely hot (wasn't noticing the temp gauge). The garage did top hose and bled the system.
-The temp shot into the red very quickly after I got it back from the garage (they warned there might be other damage) so I left it a few days, then drove it and after a few days of driving short trips where the temp would shoot into the red it eventually started behaving again.
-Had a month of trouble free motoring although the temp was getting near red then coming down to the middle area, felt that was good enough.

-After the first dilema I don't think, after usual tests, that the head is cracked.

Now:
-Temp shoots to red in 10/15 minutes and doesn't come back down, maybe a milimeter or 2 on a long straight run.
-Have done the newspaper in fan test (viscous clutch) and it stops easily when the engine is hot, from reading up on the wiki etc I understand this is not good. There is not much different between the engine getting hot quickly when sitting in traffic or being on the open road though.
-The coolant tank is leaking from it's other cap, the small nut-shaped one with a wire attached to it. Can't find anything about this cap on the internet. This will be spurting steam if really hot, it's not gushing but that appears to be because the leak is too small. When the temp is near the blue it does leak a little bit, just trickles out.
-All hoses are hard and hot after a 10/15 min run (and temp in red)
-After the tank has finished leaking as above all the coolant pretty much has gone.

Questions:
-Why is this coolant leaking from where it is? I only fill the tank to half way half way so not sure why there seems to be so much pressure.
-Is the whole issue related to the dodgy viscous clutch/coupling?
-Is the viscous clutch/coupling actually dodgy? Some people seem to say that newspaper test isn't supposed to be the best.

[daimlerman]

Small nut shaped thingy is the connector for the coolant level light,so I presume we are talking about a six cylinder engine?

The fan only 'works' with the car below 30mph,above this speed the incoming air is sufficent to cool the radiator on it's own....so you saying the gauge is in the red at speed points to a system failure somewhere.

The leak could be due to either excess pressure or a damaged tank/fitting.
A viscous coupling is not expensive from ECP/GSF and will help with low-speed cooling.

My thoughts are more toward a damaged head to be honest,any signs of oil and water mixing?
Any steam from the exhaust?

[Captain_Birdseye]

Hi, thanks for clarifying that.

There's no steam from exhaust. The oil looks not too thin on the dipstick. No soapy smell from exhaust. (Other tests?)

I just went out and let the car idle for a bit, the revved it for 60 seconds and the water was trickling out of the connector for the coolant level light (I took it off and had a look inside to see a thingy that was obviously for that job!) I had a go at tightening it but it gets to quite tight and then clicks back up so can only tighten just over thumb tightness really.

[daimlerman]

Really,excess coolant should escape via the overflow in the tank neck,the sensor nut should be little more than hand tight.
The overflow port is clear,of course?

Real question is;
Why is the expansion tank pressurising to this extent?

Still feel that the root cause is a damaged head,the running hot will have caused damage somewhere!
Removing,pressure testing,skimming up may well be the answer.

[Captain_Birdseye]

The overflow port is clear,of course?

Is that the port for the breather hose? I've not heard of it b4.

Real question is;
Why is the expansion tank pressurising to this extent?

Good question, not to do with air lock? May need bleeding?

Still feel that the root cause is a damaged head,the running hot will have caused damage somewhere!
Removing,pressure testing,skimming up may well be the answer.

Thanks for your help, could be another excuse for my mates to tell me I'm a moron for getting an old car!

[daimlerman]

I've not heard/seen a blocked overflow either,but something is causing coolant to be forced past the level sender nut!

I assumed that you had tried bleeding the system

Older cars are fun to own/play with,as long as you are prepared to get stuck in and get your fingernails mucky!

[Quaser]

Sounds like your fan is knackered to start off with - i'd get that changed asap.

You said your hose is getting hard and hot after 15 mins - sounds like they are pressuring up - can you check the hose before and after the rad and waterpumps - maybe a dodgy waterpump as well.

The nut shaped thing with the wires, sounds like the coolant level sender - water should not be leaking from there!

[Captain_Birdseye]

I've not heard/seen a blocked overflow either,but something is causing coolant to be forced past the level sender nut!

I assumed that you had tried bleeding the system

Older cars are fun to own/play with,as long as you are prepared to get stuck in and get your fingernails mucky!

oh right, the overflow stuff seems clear, ye. The system was bled when it went in for work about a month ago, but, no not since then

[Captain_Birdseye]

it's ok now. I was fiddling with the sender cap after a run and it shot off emptying the overflow tank. noob. Bizarrely it is now running no hotter than it should be.

[Brianmoooore]

it's ok now. I was fiddling with the sender cap after a run and it shot off emptying the overflow tank. noob. Bizarrely it is now running no hotter than it should be.

I don't think that there's anything seriously wrong here. Skimming through the thread, I'd say that whoever replaced the hose didn't bleed the system properly, and now the sudden de-pressurisation of the cooling system when the level sensor cap blew off has dislodged the partial air lock.
I've come across a couple of cases of stripped threads on coolant bottles, and the only cure is replacement. Good second hand will do.

[Captain_Birdseye]

Thanks Brian, fingers crossed eh? The tank will need doing, now theres not the pressure in the system it seems not to leak so will get that done soon and it needs a new viscous just to get everything up together.

[zaust]

If your coolant cap has a failed rubber it will always boil and give the symptoms you describe.

[Captain_Birdseye]

it's happening again, should I shell out on letting the garage try and find what it is? How would I know if it's the rubber on the cap? Just by buying a new one I suppose. I'm hardly flush at the moment so the garage labour for them to possibly turn round and say 'Dunno mate, we'll just have to replace everything from water pump to radiator' would not be good.

[SGP]

I've had exactly the same prob with the coolant level sensor cap thread, I found plumbers or ptfe tape helped stop the leak. 9 times out of 10 overheating problems occur because the viscous coupling has had it. i don't know if it was mentioned earlier but the expansion tank lid should be replaced under a recall if it hasn't already been . this may have a bearing on the pressure in the system. A properly equipped workshop can "sniff" the coolant to check for traces of combustion gasses, to rule out the head gasket. You need to replace the fan coupling first though. that poor engine is being cooked

[SGP]

If only household appliances were built as well as bmw viscous couplings ! To last 20 odd years is no mean feat

[Captain_Birdseye]

Cool, I've got a new viscous from Prey, better put it to use.

[SGP]

Good stuff , btw the newspaper test is fine but you'll also notice from a cold start a good coupling will drive the fan for a few seconds after start up and then disengage - the blast of air and the noise will be apparent with the bonnet up. Also beware of faulty new couplings, if they haven't been shelved in the vertical position they more than likely will fail straight out of the box, and there are plenty of them out there. Best of luck hth.

[Captain_Birdseye]

In the end I flushed the radiator, bled and replaced the thermostat and for now it's done the trick, the most the temp needle has reached so far is the 1st mark after cold compared to wjhen it was 'working' b4 where it was at 1/2 way.

[Morat]

Well done
These engines _can_ be tricky to bleed. Your temp gauge position is fine, some cars run there, some run at halfway.