Technical Does the thermostat need replacing

[Punt0]

Hi

I want to just check before I change the thermostat, that this sounds like the problem.

Read a few previous posts, but just checking

I took my wifes punto 55sx for a drive as she said she saw a puff of white spoke out the back while driving down the motorway.

When driving the car I didnt see any smoke but the temp gauge was over the hot level, I put the heater fan on full blast on hot and the temperature started to decrease, but no hot air coming out.
When looking under the bonnet the top hose was red hot and the bottom cold.

Not sure what the smoke was unless the car was so hot it was burning oil but sure looks like the thermostat or blocked rad.

I guess for a tenner its worth changing anyway.

Many thanks

 

[bredsticz]

Do a compression test, could be a head gasket. Still smoking when the engine warms up? Its usually thermostat when top hose is cold

 

[red]

If the top rad hose is hot, the stat has opened and let water from the engine. Sounds more like a blocked rad or water pump failure. Puff of white smoke sounds ominous though! Maybe need to look for signs of failing head gasket (like unexplained coolant loss).

red

 

[bredsticz]

Compression test is always more reliable than coolant loss!

 

[Punt0]

Hi
I'm going to have a better look tomorrow but there didn't seem to be anymore smoke when I took it for a quick 20 min drive.

Checked the water level and that looked ok, maybe the head gasket is on it's way.

Car has done 55k and a p reg

Is the head gasket an easyish job.

 

[red]

bredsticz,

I agree that compression test is a better diagnostic that coolant loss or say mayo in oil, but the latter symptoms should be obvious to anyone as an indication. Compression test would be next to prove/disprove a problem but not everybody has the gear to do that. I've found the electrical method to be quite useful (picoscope with current probe to measure cranking current) but again, this equipment is not going to be generally available to the home mechanic.

red

 

[red]

Head gasket is an easyish job if you are reasonably competent. It does involve removal of an engine mount, cam belt, manifolds and a few other bits. You'd need to ensure the valve timing and cam belt tension are correct on reassembly and you might want to renew the belt as a prudent measure.

You ought to do (or get done) a compression test before condemning the gasket though (of course low compression on one or more cylinders could have other causes like sticking or bent valves but the head would have to come off for that anyway).

red.

 

[Punt0]

Took the car to the local garage and they had a free look, the guy suspects the thermostat, said its running fine and no signs of head gasket gone.

To start I think I will drain the cooling system and replace the thermostat.
Is there anything I need to know, im just going to follow the haynes manual.

i guess just drain from the bottom hose

 

[Punt0]

Changed the thermostat which wasnt that hard and it all seems ok, even decided to stick new plugs in and air filter, might as well do the oil next week.

thanks all for your help

 

[Punt0]

Just found a little leak at the bottom of the Rad, got a rad from the breakers which seems fine but the heaters are not blowing that hot, could I have a air lock in the system

 

[Scoobysnacks]

Air lock is very possible if you've not got hot air coming through. Dead easy to sort! With the engine running, park it with the nose down hill and open the rad bleed plug until coolant flows out. Close that one and then open the second bleed plug, which is up near the bulkhead. Again wait until coolant flows out.

Make sure that there is plenty of coolant in the tank before you start, and top it up if necessary, with a mixture to the manufacturers spec.

If that doesn't help then it could be a leak or locked matrix, but I've not heard of the Punto doing that very often, and a leak would have other symptoms such as water in the footwell!

Good luck!