S3 overheating when driving. Normal when idling

jamesmartin · Nov 17, 2018

Sputnik01 said:
Some thoughts on this
1) Are you getting an air lock? I had a similar situation where it (109 2.25 petrol) ran at a decent temp then as soon as I started to climb a gradient the temp shot up. It was too quick a reaction to be the actual engine temp increase due to loading. Later when I pulled the cooling system apart to replace the thermostat due to other issues it disappeared. No reason why the thermostat would be affected by gradient
2) It's not the valve timing or what ever you have on diesels that make it go bang is it?
3) Head gasket.

series engines favour the bypass unless thermostat is fully open which often old thermostats dont fully open, for hot countries and omn later engines ther bypass hole was reduced on series engines by a plate with a smaller hole fitted between bypass and thermostat housing and on later the hole in thermostat housing for bypass was cast smaller

Stormintrooper · Nov 19, 2018

I'm at a loss then. I have no reason to doubt the gauge. As soon as I let the engine idle the gauge reading goes down. I haven't tried. Leaving it sat stationary with higher revs for very long but stationary revving doesn't seem to make it rise

Only when actually driving

jamesmartin · Nov 19, 2018

Stormintrooper said:
I'm at a loss then. I have no reason to doubt the gauge. As soon as I let the engine idle the gauge reading goes down. I haven't tried. Leaving it sat stationary with higher revs for very long but stationary revving doesn't seem to make it rise

Only when actually driving

if gauge rises as revs do check alternator output at idle and when revved

Stormintrooper · Nov 19, 2018

Checked before
Volatge increases with th revs

Stormintrooper said:
Goes from between 12.4 up to 13.8 depending on revs

jamesmartin · Nov 19, 2018

Stormintrooper said:
Checked before
Volatge increases with th revs

fit a new alt then the problem goes away

Stormintrooper · Nov 19, 2018

Is my alt not working correctly? Wouldnt my fuel gauge do the same thing if it was the alternator?

jamesmartin · Nov 19, 2018

Stormintrooper said:
Is my alt not working correctly? Wouldnt my fuel gauge do the same thing if it was the alternator?

it may do but it has a voltage regulator feeding it

Stormintrooper · Nov 19, 2018

Is there a way to test it?

Don't mean to question your knowledge I just want to avoid spending more money replacing things that aren't broken lol

Blackburn · Nov 19, 2018

Try checking the voltage at the temperature sender at tickover and revs , an analogue gauge is best. Temp sender should just be getting 10V same as fuel sender , as it is switched on and off by old type voltage regulator digital meter struggles to read the changes.
You can buy electronic versions of voltage regulator which give a smooth 10V

jamesmartin · Nov 19, 2018

Stormintrooper said:
Is there a way to test it?

Don't mean to question your knowledge I just want to avoid spending more money replacing things that aren't broken lol

whats alt rise from at idle and to when revved,

nickjaxe · Nov 20, 2018

Its not right that the temp should drop when the engine idles....if the stat is working correctly it should stay the same...or raise after a while as its getting no cooling air passing through the rad.

Get an infra red thermometer off ebay £10 or less...point it at the thermostat housing and it will give you its temp...thats where the sender is.

Then you will know if your gauge is giving you correct info or not.

wireman · Dec 3, 2018

Did you ever get to the bottom of this?

Stormintrooper · Jan 12, 2019

Sadly not. New job started just before December and I haven't had time to touch it yet. Plan for today however is to get the analogue meter on it and hope the one I bought isn't too cheap to get an accurate reading lol

nickjaxe · Jan 12, 2019

The rad will go cold lower down...just doing its job...a laser thermometer is a very handy tool in the garage for checking things like this...very cheap on ebay.

I was going to say the voltage stabilizer for the instruments...that what at idle the gauge drops.

Stormintrooper · Jan 12, 2019

Tested with an analogue and digital multimeter. With engine off. Battery voltage about 12.2v

Lead to temp sensor and lead to fuel sender reading between 11.5 and 11.8 volts.

Is it weird that the digital meter had a clear reading with no jumping?

Blackburn · Jan 14, 2019

If some one has fitted an electronic voltage stabiliser the true reading will show on either meter. Sure the voltage to intruments should be 10V not 11.5V or 11.8V.
This voltage needs testing with the engine running as alternator will give out upto 14V.

Stormintrooper · Jan 14, 2019

Found a rusty voltage regulator behind dash. Figured it was knackered. Opened it up out of curiosity and it was pristine inside. Guess the part that contacts the case to earth itself had corroded too much. New one on order. Will see what difference it makes

Paulthengine · Jan 28, 2019

Just had a Series 2 in complaining of intermittent overheating, wire from temp sender resting on exhaust manifold, burnt through insulation but not making good enough connection to manifold to give full scale deflection on gauge

Stormintrooper · Feb 2, 2019

UPDATE
Changed the stabiliser.
More accurate and responsive. Still reading high under revs. Normal at idle.

Next step is a new radiator I guess

Stormintrooper · Mar 24, 2019

New update.

New rad fitted. Another new (tested) thermostat . Still over heats but slightly less.

Still goes back to normal at idle and creeps up with revs whether stationary or moving.
Checked alternator output again. 12.6 idle and 13.6 at revs

S3 overheating when driving. Normal when idling

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