Temperature rise and then suddenly goes back to normal?

[moscoworbust]

Hi,

I had a slight scare today.

I drove my car from home to the nut and bolt shop and noticed the temp had gone through the roof.

I stopped, checked if the head gasket had blown. No milk in the oil.

I think it's still blown.

I let it cool and drive to home, and then suddenly the temp goes back to normal (50% on gauge)

I imagine this is the thermostat staying closed and then suddenly opening, flooding the engine with cold water.

Correct?

[Nic]

An airlock in the system can cause the symptoms you describe it could also be a worn radiator cap leaking pressure or the thermostat not opening properly.

I'd start by fitting a new rad cap, top up the coolant to the brim of the radiator neck, then run the car on fast idle with the rad cap off, if the level drops keep topping up the coolant. Once all the air is out of the system fit the rad cap and then leave ticking over until it gets up to temperature keeping an eye on the temp gauge and checking for any leaks.

[synXero]

Could be a bad ground?

[moscoworbust]

An airlock in the system can cause the symptoms you describe it could also be a worn radiator cap leaking pressure or the thermostat not opening properly.

I'd start by fitting a new rad cap, top up the coolant to the brim of the radiator neck, then run the car on fast idle with the rad cap off, if the level drops keep topping up the coolant. Once all the air is out of the system fit the rad cap and then leave ticking over until it gets up to temperature keeping an eye on the temp gauge and checking for any leaks.

Thanks, I'lll do all that then!!

Get a thermostat anyway? only 8 quid.

[moscoworbust]

Could be a bad ground?

On the temp gauge/sensor?


When i opened the bonnet there was a lot of steam coming off the thermostat housing. It was definitely HOT!

[moscoworbust]

went for another test drive and it did it again

[Nic]

Don't drive it until you've sorted the problem, you could cause serious damage if it overheats.

[moscoworbust]

I topped up the coolant, I thought I had. I did what matey above did.

I get a new thermostat from unipart tomorrow and I'll fit it Friday.

Fingers crossed it works.

It might be the belt on the water pump slipping, or a broken water pump but i doubt it.

[moscoworbust]

Seems it may just need a bleed.

New thermostat and a good bleed. This is a great how to:

http://www.lovehorsepower.com/MR2_Docs/ ... system.htm

[bobhatton]

It might be the belt on the water pump slipping, or a broken water pump but i doubt it.

There is no way the belt can slip, it drives the cams too. If it was the water pump you would see lots of water under the car

[moscoworbust]

It might be the belt on the water pump slipping, or a broken water pump but i doubt it.

There is no way the belt can slip, it drives the cams too. If it was the water pump you would see lots of water under the car

cheers

[afennell]

head gasket, that’s exactly the what happened to me, Temp gauge used to shoot to the top, then back down to the norm. I had no other signs of hg failure .

[Bman2012]

id agree with others re H/G, but check Water pump...
My heater went hot, cold for days then gauge went through roof, H/G went, when repaired found pump had failed.

if your doing the job you may as well replace it while its apart.

[moscoworbust]

What?

You would replace the head gasket before replacing the thermostat and bleeding the system?

I'm fitting the new downpipe/exhaust and intercooler now. When they are fitted I'll bleed the system and see what happens. I have already fitted a new thermostat.

I can't believe you would fit a HG before checking the more simple things.

[cosmos]

If you are doing the head gasket and there is little sign of failure you may as well cover all bases by a new water pump at the same time is what is suggested above.

[synXero]

Unbelievably, this happened to me today, I think.

Temp rose slowly. I noticed at about 75% on the meter, and it rose very slowly from there to 3 dashes under full when I parked it and turned it off. Opened engine bay, no signs. Let it cool and drove home as I was only a minute away. Left the car and used the other.

On the drive home, the temp dropped back to normal.

Sounds like HG right... Will try thermostat and coolant top up first.

[moscoworbust]

I was hoping to top up the coolant today but i ran into problems removing th downpipe.

I need to install the new intercooler/exhaust and downpipe before I can run it.

The temp rose at the same rate from 0 to full.

If it had just smashed up to full I would think HG. But as it went up uniformly it was if the thermostat just didn't open.

I've read enough posts on forums describing this and they just needed a bleed.

Here's hoping

[synXero]

Have you tried testing by starting from cold and feeling the rad pipe that runs through front bulkhead to radiator? Apparently of it warms gently, your thermostat is gone, as you'd expect it to warm suddenly.

[moscoworbust]

Can't start it at the moment, as I said.

I put a new thermostat in anyway as I had everything out anyway for the downpipe install.

I'll check it.

[C50]

sounds like thermostat