1800: P1800 Rad/Expansion bottle problems

[142 Guy]

Originally Posted by Kevin 1964

Regards the leak, it always comes from the top of the expansion bottle where there are 2 x small holes just below the cap, never the rad cap.

That is the correct location for venting due to pressure release from the pressure cap.

Did the venting problem occur before you replaced the expansion bottle cap or after? If the problem occurred after the pressure cap was replaced, I might be inclined to think that there is a problem with the new cap. Either it is not sealing properly on the bottle or it is opening prematurely. If the problem occurred with the old cap, then I am at a bit of a loss.

One thing I don't recall you mentioning is what the dash temperature gauge is doing when all this drama with venting coolant occurs. Are you actually overheating according to the gauge? If not, that might suggest that the problem is premature venting from the pressure cap. If you are overheating, then something else is likely at play.

Does your 1800 have the oil to water cooler? If so, is it possible that when your shop was doing the hose changes they messed up the reinstallation - I am really reaching with this one!

Do you have access to one of those hand held IR thermometers? If so, when the engine is running and the thermostat is open take a temperature profile horizontally across your radiator near the top, middle and bottom. A discontinuity in the temperature profile indicates a blockage in the radiator. That might be due to sludge blocking the tubes (depending on how they did the flush when changing the coolant they could have moved 'stuff' in to the radiator. I have also been party to two horror stories. One involving a piece of rag being left in a hose during replacement and finding its way into the rad tank and blocking some of the tubes causing an overheat problem. The second involving a rag stuck in the lower rad hose restricting coolant flow.

If you don't have an IR thermometer, you can do a hand test. After the engine has come to operating temperature shut the engine down. Run your hand across the rad checking for significant temperature differences. Difficult to do with the grill in place and a fan and shroud on the back side.

[Ron Kwas]

Kevin;

"Regards the leak, it always comes from the top of the expansion bottle where there are 2 x small holes just below the cap, never the rad cap. To make matters worse, the new cap seems such a good fit, that after the last overflow yesterday, "

...those two holes are the intended point of pressure relief when the pressure in the CS exceeds the Cap rating, and if the Exp Bottle is overfilled when CS is cold (when it should be at Min level) OR if CS boils (due to air pockets or other reasons) and the resulting expansion fills the Exp Bottle with eventual overflow. Normally the level in the Exp Bottle should vary between Min and middle when cold, and somewhere below Max when hot...with no overflow! I recommend you remove Rad Cap and fill and burp your system completely before turning the (strictly minor) auto-burping over to the Exp Bottle.



Cap on the Radiator is strictly there to seal off the Rad after filling CS...NOTHING should be happening there once it is in place and sealed, see graphic!!
Source: https://www.sw-em.com/Cooling_System.htm

Good Hunting!