expansion tank

[craigh]

has anyone fitted an expansion tank to their system as well as the gd supplied header tank? my engine seems to kick out a fair amount of water via the spill off hose on the header tank,leaving me short of coolant when i forget to check it before a run
im running a ford 302

[SimonP]

Craig,
You shouldn't need anything else, provided that:

1. You only fill the tank half full, when the engine is cold.

2. The UNDERSIDE of the top hose at NO POINT is EVER higher than the coolant level in the tank.

Example, if you have a stat housing with 45 degree upward outlet, then you use hose bends etc to bring this back down to your header tank inlet, you will have problems because the water pump doesn't have enough "oomph" to push water over it at idle. - Hence the water in the engine will start to boil, pressure will increase and some will be blown out the pressure relief outlet.

As long as your top hose remains about a quarter full of water at all times, you should not have problems.

If this looks OK, verify the engine temp and radiator inlet and output temp with an infra-red thermometer, as the dash gauge will likely be inaccurate (mine reads about 98 when the real temp is 87).
If the rad inlet temp is a lot lower than the engine temp (on stat housing) then coolant is NOT CIRCULATING properly.

Note - if you have a chromed stat housing, you will have to temporarily apply some matt black paint or insulation tape to it, in order for the IR thermometer to give a true reading.

If this all still looks OK, it may be worth having the system pressure tested - a minor head gasket leak can cause coolant to be forced out due to system over-pressure. The leak can be so small as to let gases into the coolant, but not allow coolant into the cylinders.
They should also be able to test for the presence of combustion gases in the coolant.

But, first things first, make sure the system can flow properly.

Simon.

[maxGD059]

Craig,

I run a hose from my GD header tank to a standard SD1 expansion tank. I did this as I had so many cooling problem due to airlocks. Although not strictly necessary, it has the advantage that you can see the coolant level when the engine is hot, & don't have to run the risk of burns when removing the header tank cap. It also means on very hot days you don't piddle coolant out!

[SimonP]

Richard,
I take it that you would need to use a "plain" cap for the GD header tank and the pressure cap on the SD1 expansion bottle with that setup for it to work properly?

Simon.

[maxGD059]

Simon

That's right -found a nice chromed shiny one at Stoneleigh one year for a few quid & the system works very well. No worries about burnt hands checking the coolant level when the engine is hot. Must get a nicer expansion tank as my prehistoric SD1 item is fairly crappy & a bit embarrassing