The Stovebolt Site Forums The Shop Area Engine Shop Help with Overheating problem (1952 GMC 228)

Update this morning.

By the way, the coolant is Walmart house brand ethylene glycol that I mixed 50/50 with distilled water. Color when new is kind of [censored] yellow. When I drained the antifreeze/water mix
last night I ran it into a non-transparent container. This morning I decided to pour some through a clean white rag to see if there were any large chunks of rust or whatever in the mix.

Found 2 interesting things.

The color of the mix now has a definite dark brown coloring when you are looking through more than an inch of liquid in a clear glass container. After 3 or 4 inches a light will not shine through the mix. Looking at the color through the clear plastic radiator catch can hose (5/16" ID) it was closer to yellow, but still had a brown tinge to it and you can see small "blobs" of the slime in the hose. If you drain the hose much of the slime remains in the hose until forced out with a water stream from my garden hose. The clean white rag that I poured the coolant through was yellow and had small amounts of the same "slime" in it. There were no "chunks" of material caught in the rag.

The upper part of the thermostat housing (where the top radiator hose attaches) was left on my workbench overnight. It also had some of that "slime" noted above in it. When I looked at it this morning the inside had dried leaving behind a yellow (antifreeze colored) powder deposit. The deposit rubs of easily with just a touch of my finger.

I also tested the accuracy of the mechanical temp gauge (the one at the rear of the head). I boiled a pot of water and immersed the bulb (after wiping a small amount of that same slime from it) in the pot. By the time I got the pot from the stove in the house to the garage 100+ feet away and sitting steady under the hood my IR thermometer measured the water temp at 186 degrees and the truck's mechanical temp gauge read it at 193 degrees. Not exactly equal, but not so far off that the 230 degree reading I had yesterday morning was just instrument error. I gotta believe the engine was really hot.

Question: Could the "slime" be the result of insufficient rinsing after using the 1 pound of citric acid per gallon of water flush mix? I have used this method before (in another truck as well as this one) and did not experience slime.

Plan for the rest of the morning is getting the truck's nose pointed downhill to drain as much more of the coolant out. I may even try blowing through the radiator filler with my shop vac to get as much more of the coolant mix out as I can.

Then back to draining the system by running the garden hose into the running engine with all draincocks open and enough flow to slightly overflow the radiator.
Question: Should I do this with or without the thermostat in place? If you answer, please state why you have that opinion.