88 DegC stat and Temperature gauge error

[The Hatter]

I recently fitted an 88 DegC stat to my 350i and was alarmed the first time I drove the car to see 115 DegC on the gauge...

BUT... it didn't boil over. Using an infra red thermometer I checked the actual inlet manifold temp around the gauge sender on the driver's side and the CTS/thermotime switch on the passenger side and it's approx 95DegC when the gauge is reading 115; plus the (new) radiator fan switch is switching the fan on and off which agrees with a coolant temp of 95ish at the thermostat housing.

So... I think the gauge is telling porkies. Plus with the 88 DegC stat the engine is running really well (as if the ECU temp sender is reading correctly) and the heater works very well!

Anyone else checked their engine temps with an IR thermometer on the inlet manifold? Or have reason to not trust the gauge?

[adam quantrill]

Quite often you find a series resistor in line on the sensor to adjust it back. Let it get up to temp then put in a hundred ohms to adjust the gauge - if not enough add more resistance. Or you could use a 1k ohm pot to start with - ajust ti till its right, measure then get the nearest resistor. You can put it on spade connectors and in shrinkwrap to make a neat job.

[RCK974X]

agree with that, but if it's a hot wire type gauge (i.e. standard Lucas type) 100 ohms is probably a bit big IMHO.
I would reckon starting at about 20 ohms or so would be better....

My 280 has a 15 ohm resistor in series, which brought the (SW) guage down about 10 percent of its full scale.
It now sits exactly half way at normal cruising.

Edited by RCK974X on Thursday 5th December 00:39

[GV]

I tested mine with with IR laser and found my temp gauge was not out by very much.