Occasional overheat

[ed1801]

Hey there,

My Ph1 172 is playing up.

About 1 in 20 times (guess!) I take it out and drive it, after about 5 miles it will overheat. I stop/pull over and after a minute or so the temperature gauge zooms down to normal (in a couple of secs) and everything is fine.

Looks to me like the thermostat isn't opening correctly/everytime.

I changed the coolant and the old thermostat as that had stuck open. I'm wondering if i bled it properly.

I reassembled and filled it up, then loosened the bleed screw until no air was coming out. I then started it and left the bleed screw loose until no air came out - the thermostat had opened before i decided all the air was out.

I have no loss of coolant, everything else about the cooling circuit looks good.

Any suggestions?

Thanks

 

[ed1801]

Ok, so it did it again this morning.

It is definitely that the thermostat isn't opening correctly. As I drove to work the temperature gauge started at cold and just went up and up. I stopped (presumably allowing time for heat to soak into the thermo and open it) and the temperature goes back down. After it has done this, everything is fine no matter how long i drive for.

Can I confirm that there is only 1 bleed bolt on the thermo housing and there isn't a sneaky one anywhere else? If i squeeze the rad top hose, it feels like there could be air in it..... It kind of gurgles and bubbles.

Can someone also let me know the correct bleed procedure so i can do it again?

Thanks for your help,

Ed

 

[pinky]

I would say its the thermostat..are the pipes at the top hot and the ones at the bottom cold?.
sorry dont know about bleeding.

 

[ed1801]

Hey there,

Thanks - the thermostat is definitely shut - the rad top pipe is cold and then suddenly heats up - it is like it is sticking shut, but it is a brand new thermostat.

I think that there is air in there and so only a bit of the thermostat is heated by water meaning you have to wait for the heat to conduct through the thermostat body to open it, hence the delayed reaction for it to open up. I can't get the air out though - I've bled it twice now..... Unless I'm doing something wrong.

I would say its the thermostat..are the pipes at the top hot and the ones at the bottom cold?.
sorry dont know about bleeding.

 

[pinky]

Maybe put up another thread with the title..how to bleed the coolant system.

 

[mattjk]

I dont think Its due to air being in the system. What coolant and mix are you using?

 

[bmh.01]

Heres the filling/bleeding procedure:
http://www.getflat.co.uk/pics/3286A-110-111.pdf

Assuming the thermostat is in the right way round and it definetly works? (tested it?)

Also you only really want to be using the proper premix renault type d coolant.

 

[mattjk]

Comma Xstream red is also fine!

 

[ed1801]

Yes, I didn't quite do that procedure - I left the bleed screw open much longer.

I'm using the halfords long life pink stuff mixed 50% with deionised water.

I will try that procedure again tonight and report back!

Thanks for all your help

Heres the filling/bleeding procedure:
http://www.getflat.co.uk/pics/3286A-110-111.pdf

Assuming the thermostat is in the right way round and it definetly works? (tested it?)

Also you only really want to be using the proper premix renault type d coolant.

 

[ed1801]

Ok, so i undid the bleed screw when cold and loads of air came out. I'm guessing this is the source of the problem.

Did back up and ran engine for about 20minutes till the therm opened, and it sucked in a whole expansion tank worth of coolant! So the rad must have been half full of air too!

So it is a double mistake on my part. Bear with me though - i'm used to my mx5 which didn't have any of this bleed screw business.....

Thanks for all your help!

Cheers

Ed

 

[bmh.01]

You didn't let the tank level fall to the lower opening did you? Otherwise it will have sucked another load of air in, you need to keep coolant in the tank while its sucking a load in.