Temp guage says overheating, but car not?

[Daves8]

My 2005 VZ calais was a erratic temp guage. It will tell me it is overheating, and the warning in dash reads engine temp hot..... but i lift bonnet and not heat or steam, and the overflow bottle coolant is normal temp...

The guage will then swing up and down rapidly (say 1-2 seconds to go from almost red (top) to half.....)

This has happend a few times, we put it on a code reader, but nothing was detected.

I understand it may be the sensor or switch?

Has this happended to anyone else, and was it expensive to fix?

[Fnomna]

My VT has started doing this once in a while. Even on a cool day it might shoot up to hot, the temp warning light and buzzer goes on, but then after a minute it will go quickly back down to the proper temp. The thermostat's only a few years old. Seeing how quick it went back down makes me think it's not actually overheating, but may be a sensor or wire.

My wife's Vectra does a similar thing, but will stay indicating hot until the engine's switched off. Then if I switch it back on straight away it shows the right temp, so I'm pretty sure that's a sensor or wire too.
I might try doing this with the VT next time too and see if that happens.

I'd like to hear any definite answers too.

[HSV Listy]

Are you sure your thermostat is working. Sounds like it is sticking and then letting go so there will be no water flow inside the engine. Then again it could be a electrical fault with the sender. Get some boiling water and cold water and put the sender in that to test it and see what the guage does.

[SharkBiscuit]

It's just started happening to me over the last few days as well. I've done around 300 k's in that time and it's happened about 4 times.

The car's not steaming or low on fluids and it seems to kick in when cruising or idling at lowish revs.

The classic scenario seems to be in sixth doing 80 k's.

The engine doesn't seem to be unresponsive when the guage is high and in fact it seems to resolve itself when I drop a gear and give it some revs ie still doing 80 k's but in fifth.

I'm also finding that the fan is running for some time after the engine is switched off as well.

Needless to say, I'ts going to get checked out ASAP incase it is anything other than a misread of the actual temp.

[Daves8]

Sharkbuscuit can you let us know once you have had someone look at it, as i dont have time over the next week or so to go see Holden.....

Cheers

[ova400]

I would say at a guess its the sender, I had a similar problem with the sender playing up, a new one sorted the problem quick smart.

Have a look at the sender in the top left of the passenger side head make sure its not brittle and cracked allowing a bad connection and when this comes out the temp goes straight up.

Next time it happens try to jiggle the connection and see if that fixes it and theres your problem

[SharkBiscuit]

I just had a chat to my workshop and a suggestion was made of thermostat issues or perhaps wiring.

Until it's investigated though, it's speculation.

I have the car booked in next week. (and to get a Tru Trac installed :woot:)

[TERRAFIRMA]

its possibly just a bad earth on the sender??

[Daves8]

Whilst the bootle where you put the coolant says full.... the radiator cap took over 1 litre.... the handbook says fill and check through the coolant bottle, but a mechanic told me to check radiator.... as low water can prevent a proper earth.....

May have fixed the problem, but i will wait a week to be confident it fixed it.

[Desertws6]

Whilst the bootle where you put the coolant says full.... the radiator cap took over 1 litre.... the handbook says fill and check through the coolant bottle, but a mechanic told me to check radiator.... as low water can prevent a proper earth.....

May have fixed the problem, but i will wait a week to be confident it fixed it.

This sounds like a bad radiator cap. If the cap seal (and or filler neck issue) is bad it is possible to weep enough coolant when hot and draw air in when cold, leaving the bottle at the same level.
It's work having a look at!

Cheers,
Steve

[Growler]

This sounds like a bad radiator cap. If the cap seal (and or filler neck issue) is bad it is possible to weep enough coolant when hot and draw air in when cold, leaving the bottle at the same level.
It's work having a look at!

Cheers,
Steve

I had exactly the same problem with my VZ, and yes it was the radiator cap apparently it is not an uncommon problem with VZ's.

[fireguard]

I had a similar problem with my old vt. Turned out it was a dodgy thermostat. Maybe look into that?

[SharkBiscuit]

Mine has been resolved now and the cause was most likley the thermostat (now replaced with a cooler thermostat) but my water pump also had a suspect leak so was replaced as well as a coolant flush.

Pretty much covered all bases :)