Temperature gauge of the scale past red and blowing cold air

Post Mon Sep 25, 2017 8:21 am

Hi all,
I've had a temperature gauge that has been jumping around for a while now on my 1989 BMW e30 320i Convertable and I previously took it to my mechanic who said it wasn't over heating as the the pipes from the radiator could still be squeezed when it was showing very hot.
This weekend I took the car on a 160 mile round trip and before the journey back topped that coolent level up but didn't tighten up the cap totally on the water/anti freeze top up bottle in the engine.
When we hit traffic almost home I noticed the temp gauge had got so hot that it had gone past the danger red zone and was as far right as it could go,I turned on the hot air on in the car which was very hot to try and cool the engine but then it started to blow cool air.
I pulled over and let it cool down and there was steam coming from the slightly lose antifreeze/water cap so I let it cool slightly then put more water in.
Considering the gauge was past the red the car didn't seem to be acting that strange and I checked the dip stick and rocker cap and there is no creamy colour in there.
Any ideas ?

Post Mon Sep 25, 2017 9:08 am

Firstly when cooling sys is running correctly. its running under pressure as a seal system, with a sealed cap
as the Coolant water is pressurized the boiling point of the coolant is raise. that's why yours was boiling and loosing water as steam.

I don,t know why your temp gauge is all over the place, its probably the wiring /connectors or the actual sensor/Guauge itself at fault.

There are two rechargeable type batteries in the dash (back of) which are suppose to last 4-6 years.
Some one on here will know their function, something to do with service indicators ? I don,t know if they affect the gauges.

Sounds like your lucky and have not done any damage to the engine. as you stopped.

Post Mon Sep 25, 2017 10:47 am

Jumping temp. gauge is probably a loose small brass nut on the back of the instrument cluster housing. Common fault.
What has happened since is purely because you left the pressure cap loose, and it boiled, and blew out most of your coolant, before you noticed the gauge. Heater went cold, because there was insufficient coolant to fill the pipes, and circulation to the heater stopped.
I'm unclear as to whether the heater now works, but if it doesn't, you have an airlock in the top heater hose from the bulkhead, which is most easily cured by removing the cap from the coolant bottle, removing the top heater hose where it connects on the bulkhead, pulling the small rubber overflow pipe from the coolant bottle back into the engine bay through the hole in the inner wing, placing the open end of the pipe in your mouth and blowing gently while holding the palm of your hand flat across where the pressure cap fits.
This will lightly pressurise the system, and force coolant from both the stub pipe on the bulkhead and the heater hose, so push the hose back in place while this is happening.

Post Mon Sep 25, 2017 11:45 am

Thanks guys,thought I was in bad trouble for a moment there but looks like I'm o.k.
Thanks for all your help and advise:-)

Post Mon Sep 25, 2017 1:41 pm

Joedean wrote:Thanks guys,thought I was in bad trouble for a moment there but looks like I'm o.k.

Time and miles will tell! If your car had the 2.5 litre version of your engine instead of the 2.0 litre, there'd be a very good chance that you would now have a cracked cylinder head, but the smaller engine is more tolerant.
It illustrates the importance of keeping things in full working order. If the gauge needle wasn't already prone to jumping around, you may have noticed the climbing temperature earlier and saved stressing the engine so badly.
There is provision on the instrument cluster circuit board for an excess temperature warning light, similar to the low fuel light, but no E30 I've ever seen has had it fitted.

Post Tue Sep 26, 2017 9:16 am

I'm hoping it was a crazy coincidence that I didn't tighten the coolant cap and the temp gauge finally broke at the same time as after starting the car from cold this morning the temp gauge goes off the scale again after about 7 minutes from starting the engine stationary and the engines is no way that hot! Have my mechanic coming on Thursday to take a proper look.
Fingers crossed.

Post Tue Sep 26, 2017 10:00 am

Do you have a working heater? If not, you have the airlock I referred to in my last but one post. This MUST be dealt with or you will crack the cylinder head.
Follow the simple instructions in my post.

Post Tue Sep 26, 2017 10:23 am

Thanks Brian,I need to wait for the thermostat to kick in before the heater will blow hot apparently when starting the car from cold which my mechanic says would normally take about 15 mins.
I'm going to leave it to him but will definitely show him your post if he doesn't already know.
Thanks for helping,appreciate it.
I love that car.

Post Tue Sep 26, 2017 10:30 am

M20 engine should start producing noticeable heat from the heater within a couple of minutes at most, usually less. It uses a bypass system with the thermostat that diverts the water away from the radiator during the warm up phase, so ALL the heat produced by the engine at this time is delivered to the heater.

Post Tue Sep 26, 2017 4:19 pm

o.k well that's not happening so will inform my mechanic.Thanks !!!!!

Post Tue Sep 26, 2017 4:54 pm

I've had an experience similar. Mounted on the hot feed pipe to the matrix was a small valve, over time it got full of tiny bits of debris in the water. Literally just fine particles of rust. I drilled out the rivets holding it on, cleaned it out and refitted it using bolts. The problem was sorted after that.

Post Wed Sep 27, 2017 9:32 am

steve3smart wrote:I've had an experience similar. Mounted on the hot feed pipe to the matrix was a small valve, over time it got full of tiny bits of debris in the water. Literally just fine particles of rust. I drilled out the rivets holding it on, cleaned it out and refitted it using bolts. The problem was sorted after that.

The matrix on my Merc 190 was so packed with gunge thatit was giving out no heat- i resorted to using limescale remover- it took the better part of a morning before it ran clear.

Post Wed Sep 27, 2017 9:59 am

Any half decently maintained E30 won't have gunge and rust in the cooling system!
It's important to maintain anti freeze strength and renew according to the service intervals. The aluminium alloy cylinder head will corrode at an alarming rate if this is not done.

Post Wed Sep 27, 2017 6:35 pm

Im going to raise all these points with my mechanic friend tomorrow so thank you.
I'll keep you posted if youre interested to know. As I said,love that car!! fingers crossed.
Can't upload photos on here can you ?

Post Wed Sep 27, 2017 9:09 pm

Joedean wrote: Can't upload photos on here can you ?

You can : instructions are at the top of the 'for sale' forums, BUT there's a whole new look to the zone coming soon (up and running right now,for testing, in parallel with this one), which will allow you to upload photos much more easily.

Post Sat Sep 30, 2017 10:22 am

Hey peeps,
Yes you were right guys,air lock so topped up,took ahout 3 litres of water :-/ but I'm told the coolent system in total holds about 20 litres.
Bleed the air lock out and the heaters blow hot and the needle on yelp gauge is sticking in just a tad over half.
My mechanic said all the pipes where the same temp, the engine was running. Really smoothly and there were no sigjns of damage

Really happy.
Thanks for all your advice.