Engine temperature query

[Adil786]

The temp gauge never goes above 1/4 mark these days, it used to sit perfectly in the middle. What's wrong? I did some research on the zone and carried out a couple of tests:

Car idled for 20mins, interior heater off. Measured resistance of water sensors (on the sensors themselves, not at the cluster/ECU, don't know what pins??), results as follows:

Blue (hot) - 352ohms
Brown (hot) - 42 ohms

Measured against a chassis-earth.

I changed the viscous for a sachs one from ECP - twice - as it feels too stiff cold. This thing shreds newspapers at any temperature! Is there a torque vs temperature chart available?

Also the cooling system has lots of antifreeze in it as I got the mix wrong. Maybe 50-60% antifreeze (blue stuff).

I'm going to check the instrument cluster earthing tomorrow, any other ideas? Tempted to get a thermometer and measure the coolant manually!

TIA

[eltel]

possibly your thermostat is stuck open?? more coolant will bring the boiling point down, check the brass nut on the rear of the temp gauge..if it is loose it may be a false reading..not sure what ohms the brown sensor is suppose to be but that could also be faulty

[Adil786]

thanks for the reply eltel. thermostat was replaced about 8 months ago, but it could be that again. I'll put the kettle on tomorrow and test it.

i can't see how additional coolant has much to do with it, the water never boils as it's under pressure, and I can't imagine the BP changing much between the 33% recommended concentration and 50%...but I'm happy to be corrected! I think i read somewhere that alcohol makes the coolant heat capacity drop wrt water, so in (my) theory it should be getting hotter for the same energy put in from the engine - assming the same heat transfer rate....sh1t my heads hurting with all this science!

right - will check earthing then stat.

[eltel]

i worded it wrong the boiling point goes up, i was always told that more anti freeze makes the engine run cooler cos it alters the boiling point. so neat water would run hotter than water with a few litres of anti freeze..i wont stick my mortgage on it but that is what someone said on here..and agree dont think it is the cause of your temp loss but again, a little lost through the concentration of anti freeze plus a slightly open thermostat and a brass nut slightly loose on the instruments could all add up ??

[Alex]

thermostat ?

[HJG-E30]

There is nothing wrong with the gauge sitting in this position. As long as it isn't in the blue or red section when driving (warmed up) then there's nothing to worry about.

[Brianmoooore]

Adding antifreeze raises the boiling point of the coolant, but also reduces its capacity to transfer heat.
Neither of these has anything to do with the temperature that the engine runs at if it is correctly designed and fully functioning. The engine running temperature is set solely by the coolant thermostat.

[Adil786]

mr moore you're right as always. Stat replaced and it's now back in the middle. Was a warranty job, was less than a year old too!

Thanks all

[KimH]

Mine 325 rises to 1/4 within 5 miles and then sits there rock solid once warmed up
since I got it 3 years ago. Unless anyone can offer a valid reason to meddle with it I see no reason to change anything.

I've become used to cruising along with diagonal needles: 2.5k rpm, 65 mph, 1/4 temp, 30mpg and nearly empty. With the temp sitting at 1/2 I would have to fill up, drive faster and return 15mpg to achieve the same effect.

[Adil786]

Haha I like your reasoning kimh!

If you change your stat your car will get to optimum temp quicker and will be more fuel efficient. Cooler engines burn more fuel. Stat is easy to change too

[schnaarf]

mine used to sit just below half then changed the thermostat now its just above 1/4

[Brianmoooore]

Where the needle sits depends on the rating of the thermostat fitted.
On UK spec. E30s the needle sits just above the quarter mark on six pot engines, and just about on the centre mark on four pot motors.
Don't forget that the scale is not linear, and there's only a few degrees between the quarter and half marks.