Thermostat housing
Like others in this thread I've suffered leaks from an adjustable outlet thermostat on a 302 V8. I too have resorted to the RTV sealer route. Crude compared to the elegant O rings supplied but effective! The main issue seems to be in the by pass tube area where the clamp is weakest and there are two O rings. Here's a few notes that might help others like me that need to fit this type of stat in order to plumb up their engines in the back of a GT4O:
- use best quality clamps, not junk jubilee clips
- first check where the leak is coming from. It took me a while to nail it and I feared it was the water pump as well. Water with anti freeze is very viscous and initially almost every hose clamp had to be torqued up very hard. Water then drips around the front end of the engine giving rise to all sorts of theories of the source. The source was only confirmed by pressurising the system by putting a couple of Ts in the rad to header tank bleed pipe one for air pressure and the other for a gauge. I've got a 13 psi system so that's the pressure I used.
- there's no need to empty all the coolant. I sucked out the header tank with a syringe then blew some more out from the rad bleed pipe into a container by slightly pressurising the system
- first check the mating surfaces are clean and flat
- superglue/CA the stat in place in the housing. Because it fits vertically and the recess is shallow, this stops it slipping down onto the main O ring
- I used Loctite RTV grey sealer which is specifically for water/glycol joints. In UK it's readily available at Halfords
- use the RTV sparingly only on the stat housing face and O ring face and check for zero blockage by blowing back through the by pass hose which goes to the water pump. I left the O rings in place having lightly glued them in place to the housing
- I did not RTV any other area or the other O rings around the rotational element and pipe. They did not leak but if they had I'd probably have had to weld up the housing
- mark up the final position of the pipe and hold it there during fitment. I also marked up the position of the body to the inlet manifold to make lining up the bolts easier.
- use longer bolts than supplied in order to get max torque and clamp but check they don't bottom out
- my water pump had a lug right in front of one of the housing bolts. I cut it off which made bolt access easy. The other bolt was still a quarter turn at a time bitch!
- leave the RTV to cure overnight then check for leaks by pressurising the system empty. Mine was still losing pressure on the gauge but it was easy to go round with a plastic tube to my ear as a stethoscope to find a couple of clamps that needed more torque. My reasoning was that if the system held air pressure then it should hold water!
- I should mention that the housing had to be modified. Sod's law had meant my desired position for the pipe coincided with the by pass tube. So I cut this off flush then drilled, tapped and plugged it. I then drilled, tapped and fitted a new by pass outlet on the side face of the housing.
- refill the system. I've got a bleed from the rad to header tank but even so it took a couple of short engine runs with the cap on and top ups after each short run with a keen eye on the temp gauge (I've got a cap with a pressure release lever which makes this process safe and easy). Remember the gauge sender is unlikely to give a correct reading if there's no water around it. So short runs only until the temp stabilises.
Just another few days in the building of a GT40!!!!
Cheers
Roger Allen
