Mechanics

MODELS TEMPERATURE GAUGE

1990 BMW Other

Engine Cooling problem
1990 Other BMW Models V12 Two Wheel Drive Automatic 200000 miles

I replaced the water bypass pipe on my 1990 750IL. My question is the temperature gauge is supposed to be between the 2 color zones and its only registering a quarter of the way. Do you know why it would only register a quarter of the way?
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Srt8man
September 8, 2010.



Hi srt8man. Welcome to the forum. There can be a wide variation in gauges, sending units, and thermostats. I have two identical Grand Caravans with the same size engine. One reads lower than quarter scale but goes up to almost half scale when pulling an enclosed trailer that's bigger than the van. The other one reads about 2/3 scale all the time. The heaters on both will roast your hand if you hold it there long enough.

What's important is the actual coolant temperature. If you start with a cool engine, you can leave the radiator cap off and pop in a small thermometer and watch it as the engine warms up. If it never gets close to around 190 degrees, and / or you already see coolant circulating, the thermostat should be changed. An engine that's running too cool will not get its normal fuel mileage. If you do find the coolant is up to at least close to 190 degrees, you can try a different sending unit for the gauge but they normally give very little trouble.

Caradiodoc

Caradiodoc
Sep 8, 2010.
Was it reading normally before the bypass hose got changed?

Dr. Hagerty
Sep 8, 2010.
It's never really read right to begin with but it was between the 2 color zones most of the time.

Tiny
Srt8man
Sep 9, 2010.
Hi guys. It would be appropriate to delete my first reply and let you guys figure this out between you. Dr. H, do you have the technology to delete this and my first reply? Go ahead if you can, otherwise I'll do it in a day or two.

Carry on. : )

caradiodoc

Caradiodoc
Sep 10, 2010.
It never really read right is the phrase I have keyed onto here. The instrument cluster in the E-32 cars was an analog gauge and it lacked ability to calibrate to a range, it simply displayed a temperature. The newer cars BMW produces are digital function to allow the gauge to read at one point ( 12 o'clock) regardless of the actual temperature of the coolant, what this means is that the older cars may be within the " normal" range of temperature and the gauge reads where it reads, newer cars hold the gauge at one point to allow customers to " see" normal temperatures, even if there is an excursion. Analog gauges have suffered from sender failure, added resistance in the connection/wiring, poor grounds and/or power that change the gauge reading. I recommend changing the thermostat and see if the gauge reads the same. Then we might need to go after some other aspect of the coolant temperature indicator.

Dr. Hagerty
Sep 10, 2010.