dhubbard

I have a 90 GT that is leaking coolant. I pressurized the system today and found that at a minimum the lower radiator hose is leaking near the thermostat. It appears another hose is leaking but that is coming from the oil system, so I'm confused. I posted a photo to help explain. The red line shows the other line that seems to also be leaking right at the Y connector. Can someone confirm what this hose is and if water flows through it in a late model 928?




Thanks,
Dustin

FredR

The other hose is one of the breather hoses where the petrol tank vent gets sucked through - no coolant in that.

The coolant hose is either shot or you have corrosion on the thermostat housing creating a leak path.

dhubbard

Ok thanks. I’ll start with the hose. One more question. Do I have to drain all the coolant again to do this job? Even from the engine block?

Mrmerlin

drain the radiator put a pan under the front of the oil pan so you can drain the 1 inch line, pull it off the water bridge and drain it after the radiator is empty.

NOTE I suggest replace all of the hoses
2 big rad hoses,
1 inch hose water bridge to the fender well ,
vent line water bridge back to the coolant bottle,
cap for coolant bottle,
a new heater control valve and short hose,
new thermostat and O ring and rear seal
if you get the hoses from Roger ask for the thick ones,
they cost more but last longer and you can usually use the old clamps.
For coolant I suggest to use 2 gallons of Zerex G05 and 2 gallons of distilled water.

With a coolant swap , then drain the block and flush the bottle and the heater core with water

dr bob

Kudo's for pressurizing the system cold to find leaks. This relatively simple method is too often forgotten.

There's a fat seal around the junction of the thermostat housing/hose nozzle to the water bridge. They don't go bad usually in maintained cooling systems, when there's less risk of corrosion damage to the interface point there. Sometimes a thermostat is installed incorrectly, with the seal behind the thermostat rather than in front of it. If you haven't replaced the thermostat recently, plan to drain the coolant via the radiator drain, remove the hose, then the three 6mm bolts after you may need to loosen the fuel inlet hardline into the bottom of that damper for access. There's a rear seal in the water bridge opening that deserves renewal, then the thermostat itself, then the fat o-ring seal, then the housing goes back on. Inspect the groove/recess in the water bridge, and the ledge on the thermostat housing for corrosion and repair/replace as appropriate. Draining the system via the radiator drain will drop coolant level in the block down to the bottom of the thermostat opening, so plan on managing a little coolant that will come out unless you drain a little more via a block galley drain.

If you still have original coolant hoses, replace those now per Stan's guidance above. Replacement hoses can be thinner-walled than the factory originals, so make sure that you have clamps available that will put the correct pressure on these connections. The original clamps are Norma-branded, and include the clamping diameter on them in MM. 25.4mm/inch and 2mm smaller than what you had originally will find you some clamps that will work. Our vendors stock Norma clamps and can help you with replacements. Else risk hellfire and eternal damnation by using common 'murican car styled screw clamps.

James Bailey

Changing just one hose is like putting in one new spark plug......

dhubbard