Temperature problems

[Nefarious]

I'm sure you're all bored with overheating problems, but if you could come up with any suggestions for me I'd be most grateful...

Noticed the other day while sitting in traffic that the temperature was drifting north of the indicated 95 at which the fans usually come on. Fans finally kicked in at an indicated 105-106, but switched off again at around 100.

I've just been and plugged the laptop in, and as far as the ECU is concerned, everything is hunky-dorry - it's switching the fans on and off at 85C and everythign is coming on when it thinks it should.

However, 85C at the ECU equates to 105C on the dashboard - it never had this big a discrpancy before - usually dash read 94-95 when the ECU said 85.

I've been round all three bleed points and I've got water coming out, so I think I can rule out an airlock.

Can a water temp sensor fail like this (i.e. just underreading) or do they just stop working altogether?

Edited by Nefarious on Friday 19th September 16:30

[SlvrCrb]

Check the capillary tube that comes from under the front engine cover and is then routed along the o/s of the block to the dash gauge as it may have moved a bit closer to the exhaust manifold as this routing method is the usual culprit for the discrepancies in gauge/ECU readings. I re-routed mine well away from the block in the end and the gauge is now within 1-2deg of the ECU.

[Nefarious]

That is a possibility, as the car's just been in for its 12k/tappets, so I'll definately check it.

BUT - my suspicions are that the engine is actually running hot. Temp gauge reads exactly as it always did in normal running (85-95), and I'd expect to have seen a constant shift across the board if it was just that the capilary had moved closer to the manifold. Also, and I know this is completely subjective, the engine bay feels hotter than normal.

[The AJP Griff]

Best bet is to take your sensor out,and place in hot water with a thermometer to compare accuracy.Another less accurate but easier way to get a rough idea,is to see what your gauge says when the thermostat changes over from the bypass to full flow through the rad.Mine stays at stat temperature for a little while whilst this happens,before going on to climb higher once the whole system has warmed through.
If you had an airlock affecting the one sensor you would be very unlucky for it not to affect the other one as they are right next to each other.

[C3BER]

I'll go for an iffy gauge as mine does the same and it's been on the laptop more than once to check the temp.

[Nefarious]

Cheers guys.

I'll check both the water temp sensor and the capillary tomorrow...

[brakedust300]

Mine was doing this, would climb to 100 then flick about, changed the thermostat and she's been fine since, my tell tale was that when on the move it would be fine but once stationary the temp would climb.

[Nefarious]

brakedust300 said:

Mine was doing this, would climb to 100 then flick about, changed the thermostat and she's been fine since, my tell tale was that when on the move it would be fine but once stationary the temp would climb.

Do you mean the thermostat or the water temp sensor?

[smash]

Perhaps the thermostat isn't opening fully? Hence higher temp at idle as water pump is just turning over and partially open thermostat = restriction. Once the revs are up it'll be pressuring higher to get better flow? Yes/no? (I have my coat on standby!)

[brakedust300]

I replaced the thermostat, not sure what the problem was with it, the half open theory sounds good.

[Nefarious]

I think you might be right.

Just been out to look at relocating the capillary - pulled it away from the engine and wrapped in heat-shield, but it made absolutely no difference.

Taking temperatures around the engine, the water rails next to the engine were pretty close to what the dash was reading (c.105C), while the radiator top hose was c.85C.

How tricky is the thermostat swap? From looking at the part in the catalogue), it looks like its just a case of swapping hoses around... (oh, and where is it exactly?)

[brogenville]

Thermostat is an easy one. Like you said, just a matter of clamping onto the hoses. It sits just underneeth the rad top hose.

[brakedust300]

Yep, easy job! and makes a big difference!