48 Roadmaster coolant leak:

[rdmst71]

I have coolant leaking throught the radiator over flow pipe of my 1948 Roadmaster after the engine reaches operating temperature. It's a slow leak after the engine warms up and the flow of water really increases for a couple of minutes after the engine is shut off.

For years I have used straight water with a rust inhibitor, no antifreeze and no thermostat. This problem just began recently and I lose about 1 to 2 quarts of water after a 75 to 80 mile drive. Upper and lower radiator hose's seem to be in good condition, any ideas as to what I should be looking for that may be causeing this type of leak? A couple of minutes after the engine is shut off the water leak stops.

[Guest NikeAjax]

I would check out yer freeze-plugs... then your heater-core...

Good luck,

Jaybird

[Bhigdog]

Head gasket......................Bob

[jackofalltrades70]

Agree with Bob. Sounds if you have pressure building in radiator from leaking gasket.

[Guest NikeAjax]

With your engine STONE-COLD remove the radiator-cap, start your engine, then with a light, look for bubbles in the radiator: this will tell you for sure if it one of the three problems. You very likely will see the bubbles.

Jaybird

[rdmst71]

I will look into this tomorrow morning. If I see bubbles, which one of the three would be the likely cause of this pressure build up?

[Guest NikeAjax]

I would first check out you freeze plugs, as that's easiest, maybe?, look for rusty streaks, or oily streaks, once the coolant dehydrates it looks oily, coming out of them, or pits. Is there a way to look at your heater core: again, look for the same signs as mentioned before. If all check out, then yes, it probably is your head gasket--sorry!

Jaybird

[Smartin]

He says it's coming out of the overflow tube, not anywhere else in the engine.

Radiator cap sealing completely? It really sounds like it's just running hot.

[old-tank]

He says it's coming out of the overflow tube, not anywhere else in the engine.

Radiator cap sealing completely? It really sounds like it's just running hot.

Good point. Check with heat gun at the thermostat housing. Other considerations: fill level in tank (if filled to top it will always 'find it's level'...1/3 full is adequate); clogged coolant passages in block/cylinder head creating hot spots.

[bhambulldog]

I had this problem.

I replaced my 7psi cap with a 14psi cap

Also put 1/2 gallon of "Water Wetter" in addition to the water/antifreeze mix.

[rdmst71]

I really appreciate all the input on what may be causing this problem, my shop manual does not always have good trouble solution information and I find that most often the best answers will come from other Buick owners who may have experienced the same problem or one close to it.

This leak from the over flow pipe was being caused by problems in the heat conrtol valve or the heater core. Have not determined which one yet.

After doing testing for what may be a leaking head gasket, the one recommended by Jay and a similar test described in the shop manual, I ruled out a possible head gasket leak and moved on to checking out the areas around the freeze plugs and the heater core. The temperture control knob for the heat control valve which is always turned off, was turned over to the warmest setting, but I had not noticed any heat while driving.

After turning the control valve off I started the engine, let it run for about 10 minutes and there was no water leaking from the over flow pipe. I took a 20 minute drive, shut the enging off and still no water leak.

I only drive this car in late spring, summer and fall and do not need or use the heater, so depending on what it takes to repair or replace the control valve and/or heater core, I may just make sure the control valve is always off or disconnect the temperture control knob, untill some time later.

Edited September 17, 2013 by rdmst71 (see edit history)