P6B Coolant leak

AL-58

AL-58

New Member
My '76 P6B is losing coolant. no sign of it getting hot.

I've just fitted a new thermostat, as general maintenance. Hoses are all recent as is the rad cap. The car runs an OEM overflow tank (pressure cap on the rad, blank cap on the bottle) Coolant does return back to the rad under suction when the motor is cooling down, but obviously the level in the tank drops.

There is always signs of coolant on top of the valley cover gasket at the front and the rear where you can see it, it's not just residue from dealing with hoses etc.

Once I run the engine up to temp, the top hose does not get very firm with pressure. When I do squeeze the top hose more coolant leaks on to the top of the valley cover gasket running down the back of the engine. Is this likely to be the coolant pipe under the manifold that goes to the heater? Or something else(bad head gasket)?

Just trying to get some idea before I delve further into it. If it's just manifold off to change the pipe I can deal with it, if it's head gasket I'd rather drive it to a mechanic while its still driveable.

Al
 
Try changing the caps over . Blank cap on the radiator and pressure release cap on the overflow header tank.
 
It might have been much simpler than I was thinking.

I found the bolt on pipe at the back of the inlet manifold(one of the heater pipes) covered in grey silastic. Pulling it off it didn't show any obvious signs of leaks but it was a mess just the same. But just in case, I cleaned both the pipe and the manifold where it bolts to, removing any sign of old sealant. Made a new gasket and bolted it back on with a light skim of sealant each side.

So far it seems to be working properly, Top hose is getting firm like it should under pressure when it warms up. And most importanly no more coolant pooling and running away on the valley cover gasket. Looks like it was just a bad/rushed decision from a previous owner.

Al
 
GRTV8 said:
Try changing the caps over . Blank cap on the radiator and pressure release cap on the overflow header tank.
Click to expand...
It's a thought but I can't see how it would affect coolant leaking under the manifold.

BMC/Leyland cars have the run the caps both ways around. As long as you have a pressure cap that allows backflow putting the pressure cap on the rad is correct.
 
Hi Al,

Just so you know, the P6B was never fitted with an OEM overflow tank. Cars that have them fitted was something an owner chose to do.

Coolant that leaks onto the valley gasket typically will come from one of three places. Either the thermostat housing is not sealing, or one or both of the short rubber hoses at the front is/are leaking. The mild steel pipe that runs beneath the inlet manifold above the valley gasket could also have corroded and leak. The pipe stub that you refitted can allow coolant to flow onto the valley gasket but given the engine slopes back that would be unlikely unless the car was sloping down hill or you had been driving with the braking force precipitating a leak to flow forward.

Ron
 
I have an overflow tank on mine, with the pressure cap, and a plain cap on the radiator - no problems in several years.
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Agree with JP928 - everything I have been told/read says if header tank fitted pressure cap moves to tank and blank cap on to radiator.
If I am correct: with pressure cap on tank end it allows expansion into the tank as water temp rises. With pressure cap on rad end it will only get to and from tank when pressure cap is ‘defeated’ thus it opens and coolant runs into tank. Tank end pressure cap seems logical place… happy to be corrected!

Dave
 
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