Strange temperature problem

[diggerbucket 0]

Strange one this... the water temp and the oil temp are both reading about 20 degrees cooler than normal.

First thing I did was change the thermostat because I thought it might be stuck, but that didn't make any difference.

So I put it on VAG-COM while it was running, and the temperatures reported actually looked normal on the computer, but the gauges on the dash are still reading about 20 degrees too low!

So basically, the engine seems fine, fan cuts in at the right temp etc, but the gauges are wrong.

What on earth could cause this?

[Russ_vr6 12]

hmmm interestin mate what happens when the fan cuts in temp wise?

[diggerbucket 0]

Driving along normally, the water temp sits at about 70, then when sitting stationary the gauge doesn't even reach 90 before the fan cuts in. Then if I start moving again it drops like a stone to 70 again! Oil temp reads 60-70 most of the time, sometimes reads 80 but very rarely!

[matth76 1]

My oil temp reads on average 10 deg lower in this colder weather, although it does normally reach operating temp (90deg) once you get going. 20 deg lower seems quite low, and especially if it never reaches normal operating temp. My oil temp normally reaches 90-95 at normal operating temp. In this weather it normally takes twice as long to reach 90 degrees.

Have you changed your oil as that can make a big difference? Or has anything else been changed on your engine in the last few months?

[diggerbucket 0]

It's not that it's not reaching operating temp, VAG-COM confirms that it is. It's just the gauges are giving a false reading.

[Russ_vr6 12]

hmmm,really? coz since i changed my coolant and stat,my temp never goes above 70,and oil stays ay 80-85

check the big multi plug by the aux water pump mate,seen before where the pump leaks slightly and leaks onto the plug and causes all sorts of probs

[lee060 3]

long shot . but is it possible that the replacement sensors could be slightly diff or wrong in some way?

[Petesvw 0]

Maybee the dash comp is shagged?

[diggerbucket 0]

Yeah thought it could be that Pete, but everything else works fine?

Does anyone know where the dash temps are measured - do they have separate sensors?

[SiGainey 1]

Check the earths - a slightly dodgy one will result in a lower reading

[Russ_vr6 12]

the water temp sensor is in the thermostat housing-prob a blue one