Mrmerlin

leave them alone

Giovanni

My 88 parts car had a leaky oil cooler (stock rad) and a blown head gasket!

76FJ55

Have you checked the overflow line off the expansion tank to make sure it vents freely? if the vent line is pluged or restricted the overpressure released by the rad cap has nowhere to go and the rad system will over pressure even if the cap is in good shape and tries to vent at the correct pressure.

timp928

Thanks all.

The Cylinder head guy said that he thinks what may have happened is that a small amount of exhaust gas has travelled between the head and the head gasket into the water jacket....

I have ordered a new radiator (with reinforced side tanks), and am installing a pressure gauge into the sysetm so i can see what sort of pressure is being generated in the future.

I am starting a new thread on the refurbishment of the head.

Thanks for all your replies, they have been of great assistance.

regards,

Timp
90 S4
Black on Black
Queensland
Australia

M. Requin

Mt 86.5 has a coolant pressure sensor - does the S4 have this, and would it have indicated a problem?

timp928

Hi,
I know it has a coolant level sensor, not sure about a pressure sensor??

There there no alarms dispalyed (digital dash) apart from the occasional low coolant - but it wasnt overheating.

There is a small "sensor" between the coolant tank and the radiator, but i thought it measured flow for some reason... anyone know for sure??

regards,

Timp
90 S4
Black on Black
Queensland
Australia

JET951

Hi Tim , that's the pressure delay switch , its to minimize coolant level warning coming on to quickly when engine is started cold.
Regards. BB.

M. Requin

Thanks- never understood that.

WallyP

Nope - the cooling system pressure switch is to hold a low coolant warning even though the coolant level increases.

Coolant level is low - warning is set.
Car is driven, coolant gets hot and expands enough to hold the coolant level sender in the normal position, so there is normal cooling system hot pressure on the switch.
Car is shut off for a brief time, canceling the low coolant warning.
Car is restarted - coolant level is just high enough to not trip the low coolant warning, but lower than desired. The coolant pressure switch holds the warning on, so you still get a low coolant warning.
When you open the coolant tank, the pressure drops, so the assumption is that you have added coolant. The pressure switch no longer holds the low coolant warning on.
When the engine cools, the pressure drops, and so does the coolant level. If no coolant is added, the low cold level again trips the low coolant warning.

M. Requin

Thanks, Wally, very interesting. I notice in another thread that this switch often fails when the body separates (mine did) and many just remove it from the system (as the PO did on mine, but its back in now). If I understand your explanation, a warning might be set just once in a heat cycle (ie car on or off but at operating temp) and therefore a warning that is set and then disappears on a restart should not be thought to be a false alarm.

timp928

Hi Bruce, Wally,

Thanks for that impressive bit of information
I had no idea about that.

regards,

Timp
90 S4
Black on Black
Queensland
Australia