Do you want the Road Tax system to change? Do you have thoughts on the potential changes to the Road Tax system? | No thanks
97 pressurising coolant tank and other symptoms - Gary0509
I bought this car on Friday from a small garage near the end of my street, a guy who sells the odd car now and again.

I was in a rush as i had my previous car stolen and burnt out and i needed one for my business. The car had very little petrol in it (the petrol gauge didnt even move) so i literally took it for a spin down the street and back.

On Saturday i broke down on the way home from work and had to be recovered back home (the garage is closed til Monday) The recovery mechanic identified that i needed a new starter motor, 2 new coil packs, and that the header tank was pressurising. The first two are not a problem, but the pressurising, He said this could be one of a few reasons. 1) The thermostat has gone, 2) The water pump has gone 3) The heater matrix or worse, the head gasket. I just want to arm myself with some knowledge before i take the car back on Monday.

When i was driving the car i could hear a sound like fluid running, it was coming from behind the dash area by the passenger footwell. I lifted the bonnet and saw that there was water being forced out from the cap of the header tank. The windscreen seems to mist up easily and also there is a slight mist on the inside of the plastic "screen" where the speedo and rev counter etc are. The heater, i noticed dont seem to get very warm, only slightly aired.

The recovery guy said they will do a pressure test to identify the problem, but i dont want them to do the test and then fob me off by telling me it`s not the head gasket, when it just might be.

Edited by Pugugly {P} on 06/01/2008 at 11:27

1997 Renault Megane pressurising - Railroad.
The cooling system is supposed to pressurise. Pressure and temperature are directly related, the higher the temperature the higher the pressure. Holding the cooling system under pressure allows for the boiling temperature to be raised above 100 degrees celsius. The pressure cap is an overall safety valve which will lift if the pressure exceeds it's limit. As the engine cools the cap allows air back in to the expansion tank as the pressure decreases. If this didn't happen vacuuming the cooling system would occur.

Suspect the head gasket if the pressure in cooling system increases rapidly from cold. And speaking of the thermostat I'd change it anyway
1997 Renault Megane pressurising - Gary0509
So what would explain the water coming out from the header tank cap? Is this just a case of it being too full? Also, the water was really brown, almost sludge like.

Edited by Gary0509 on 06/01/2008 at 12:09

1997 Renault Megane pressurising - Railroad.
In that case it does sound like head gasket I'm afraid to say. For some reason I don't know why but Renault's do seem to suffer with engine internal corrosion more so than other makes. This is exactly what anti-freeze is supposed to inhibit. Anti-freeze does have a shelf life, and should be changed every couple of years, but maybe for some reason it goes off earlier on Renault's than on other makes, I really don't know, but it does seem to be a problem.

The corrosion (that brown sludge as you describe) restricts coolant flow, and blocks the radiator, heater matrix and causes thermostat failure. The engine then overheats, and hey presto you've got a blown cylinder head gasket.
1997 Renault Megane pressurising - Gary0509
Ah, ha! Maybe i should just get my money back, if i am able to.
1997 Renault Megane pressurising - mike hannon
IIRC head gasket woes were not unknown with early Meganes. At least one friend of mine suffered a mega bill over it.
1997 Renault Megane pressurising - Pugugly {P}
Get your money back. See HJ's frequently Asked Questions.
1997 Renault Megane pressurising - Gary0509
Cheers guys!
1997 Renault Megane pressurising - Gary0509
Can i just confirm. Will a pressure test confirm a suspected head gasket / other problem. I am willing to give the garage a chance to put things right, but if it is the head gasket, i think i`ll just get me money back.
1997 Renault Megane pressurising - TurboD
A 'sniffer test' should tell if exhauts gas is in the coolant, but by the sounds of it you can see that it is, when I had a cracked cyl head problem, bubbles could be seen in coolant expansion tank.
At that age the car is pretty worthless anyway and no way will a dealer want to spend anythng on it.
Clearly it s not fit for purpose.
1997 Renault Megane pressurising - Gary0509
Now you mention it, we (the recovery guy and me) did notice a few bubbles in the header tank when the engine was running. Only a couple of times. He did mention this was a sign of the head gasket. I think i`ve made up my mind now. Cheers all for your help.

Ask Honest John Right column

Value my car