Possible overheating, stuck thermostat?

[stiglet]

Bit of an odd one this, here goes...

Coolant level/temp warning light comes on after driving for about 5 mins or so. Checked level, all fine. Also, my dash temp gauge is now not reading much above minimum. The two symptoms started at the same time. The engine is definately getting up to temp as the the top hose is hot, and the rad fan does kick in when left idling. If anything, the hoses seem to be hotter than usual, hence my worries that the engine actually is overheating! Could just be paranoia though...

And before anybody mentions, I have very recently replaced both the MFTS and thermostat.

I'll try unplugging the level sender and see if that helps, but it's the cold reading dash guage which has me really confused

Any ideas what could cause these two symptoms simultaneously?

[S-Express]

it is possible that you have an air block.......

[220bhp]

Check that no water is coming out of the header tank.

[Flat on my back]

The dumb one...

Can the thermostat go in the wrong way round...

Sorry not you...

[stiglet]

No water out the header tank, and thermostat is in right way round.... i think! Well I replaced it a few months back and it's been fine until this started a few days ago. It can't be a coincidence that this is very hot weather too! So i'm worried that it really is overheating but I can't tell because the bloody dash gauge has stopped working

I'm 70% sure it is electrical, because all hoses are hot so it is circulating I suppose. More I think about it the more it can't be the thermostat, must be a dodgy connection somewhere...

Am I right in thinking that the dash gauge signal comes from the MFTS (which is definately exposed to hot water, granted with a possible air lock) but the warning signal for the autocheck comes from the sender on the back of the head?

[Flat on my back]

.

My Bentley is saying the MTFS is the signal source for the Autocheck system, and the rear mounted head sensor was ecu for hot and cold determination.

[stiglet]

Right, thanks very much for that

So it would seem that both problems, the dash gauge and warning, are coming from the same sendor. Why would the same sender give a cold reading to the dash and an overheating reading for the autocheck? WTF is going on with my car?!?

Oh well, when I have time and sober i'll flush the coolant and see if that does anything at all...

[220bhp]

And the one in the header tank

[bigdan]

My understanding of the MFTS is that it;
1) gives an overheat warning to autocheck at 119 degC
2) gives an overheat warning to ecu at 119 degC and cuts boost to mechanical pressure
3) sends signal to dash gauge.

As the new ones have three pins, then i guess they have 3 separate senders, two thermoswitches and a PTC thermistor for the gauge?

so yes, it would be possible for the MFTS to give both faults separatley.

I found s2central.net helpful for this info

regards,

Dan

[Error404]

I vote for expansion tank issues on this one, had similar myself a while back

Take off the tank, fill it with boiling water and some TSP powder, leave it for 5 mins then shake it like Michael J Fox on crack

Loads of gunk and skank should some out - I did mine 3 times before it came out clean and its been fine ever since

[stiglet]

You reckon it could be the level sender? I tried unplugging it between work shifts today but couldn't quite get to it, had no tools and had a fear of getting bitten if the fan came on! How would that ****** up my dash gauge though? My faulty gauge is what points me to the MFTS, or at least the connector shorting or something.

[Knight Rider S4]

I vote for expansion tank issues on this one, had similar myself a while back

Take off the tank, fill it with boiling water and some TSP powder, leave it for 5 mins then shake it like Michael J Fox on crack

Loads of gunk and skank should some out - I did mine 3 times before it came out clean and its been fine ever since

and change the cap!!!!

[Error404]

You reckon it could be the level sender? I tried unplugging it between work shifts today but couldn't quite get to it, had no tools and had a fear of getting bitten if the fan came on! How would that ****** up my dash gauge though? My faulty gauge is what points me to the MFTS, or at least the connector shorting or something.

My guess would be that the stat you got is a slightly dodgy one and the autocheck alarm is unrelated

[stiglet]

So I unplugged the coolant level sender and no change, so it isn't that. It is temp related, as firs thing in the morning it took a while before the alarm came on. And the temp gauge always sits in the same place on the gauge when it happens, between the first two dots (around 60?). After the initial warm up in the morning, any consequent journeys after that and the alarm comes on much sooner as the car is already hot.

Got to be a short somewhere in the MFTS wiring. The plug is wet and shows signs of corrosion (blue manky stuff) so i'm 100% sure it's a wiring issue on the MFTS.

[S2central.net]

Well the two alarm pins - C and R - are separate circuits from the T pin that drives the temp gauge.

C pin is alarm into autocheck
R pin is alarm into ECU / AIRCON - but not applicable to all vehicles

I'd need to hit the books to see at what voltage levels on the C pin it declares fault but I know its different from the R pin...

To check wiring you should buzz out the signal from C & T pins to the cluster & autocheck - I can help with that if need be... I have 7A schematics here Stiglet.