Leaks coolant when plugged in ONLY

[young_gun17]

93 w250 auto. The rig is cold natured and doesn't want to turn start when it gets down around 35 at night. I've been plugging it in, and I noticed that I leak about half a cup of coolant over night when it's plugged in. It doesn't leak when its warm, cold, all of the above. It only leaks when it's plugged up. Anyone else have this problem? What can I do to fix it?

 

[pausma]

first off, figure out where it is leaking, check and make sure your hose clamps are tight.
You could also pressurize the coolant system to help you find your leak.
My guess could be around the block heater. Perhaps when it gets warm it allows coolant to leak past.

 

[EDankievitch]

i know someone will disagree with me but those cheap spring type hose clamps solved much if not all my cold temp leaks the screw type would leak when they got cold.

 

[Bob4x4]

i know someone will disagree with me but those cheap spring type hose clamps solved much if not all my cold temp leaks the screw type would leak when they got cold.

Good point,I have to agree the clamps many hate I have gotten good service from and laugh at those that go out of there way to dispose of.
Take a very close look at the water pump. They can leak under very specific conditions and not while running

 

[bigceltic]

first off, figure out where it is leaking, check and make sure your hose clamps are tight.
You could also pressurize the coolant system to help you find your leak.
My guess could be around the block heater. Perhaps when it gets warm it allows coolant to leak past.

x2 on this. I had an issue with leaking coolant only when plugged in, and it was due to a loose clamp.

 

[Gumby79]

3 years ago i found a leek similer to yours.
It was the oil cooler to block gasket failed was a bit hard to find as it would only leek 1/4 cup or less over night. The complication was below -10°f +pluged in was the only condition it leeked. And i was visiting a friend in Mt apon return to west Wa. Couldn't get it to leek@ 20psi w/rad tester. There were tracks /hard water stains originating from the oil pressure regulating valve#@$%! Water from a oil gally? So I picked up a set of oil cooler ,filter head gaskets$ 17 and 35$ i figured its cracked, but start simple pullit off and look. Cooler to block failed top front bolt hole betweenthe bolt and inside premiter flowed through the bore and driped off the tip of the bolt on to the pressure regulator. Solved used the gaskets I had for inspection. May have been able to just retork it had I known for certain that was the problem. I did knotice that bolt was not as tight as the rest.
I figure the plug only aspect has to do with shrinkage deffrence between cast and hardened steel in my case. At all temps there is enough pressure on the bolt flange to keep the water in, but add thr 750w heater it changes things.
Tip
UseTp/paper towels to visually feel around. Paper towels are corcer than tp making the tp the more sensitive tool for finding pesky small leaks(1 drip/day size and up)