Life cones at you fast. I think that is a line for a commercial or something. But it sure is true. I went looking for this thread and was amazed it has been 3 months since I posted to it. I have more reasons to confirm that I am an idiot.
When I built the truck I didn’t have a crack free coolant over flow tank and couldn’t find a new GM one online. So, I put a generic O’Reilly’s 1 gallon tank on. It cracked like the first day I got the truck to temperature. I didn’t worry about it and my coolant seemed ok. Always needing a quart every month or so which I could never trace to where it was leaving from. One day I happened to see a drip from the passenger fender and followed it to the over flow tank.
Not wanting something that cracks on there ever again I bought an aluminum 2 liter over flow tank off Amazon. Around my small town running empty it was perfect. I could top off the radiator, drive for a week or a month and the radiator was still topped off the next time I checked. Problem solved.
Until I trailered my M715 to the Rally and back last March. I was down on coolant and couldn’t figure out where it went. This continued into our trip to the Rockies in June. We stopped for food in the little town of FairPlay at 9,954 elevation. Walking back out to the truck it was pucking coolant all over the place. I had just topped the radiator off that morning and hadn’t been over 214° climbing into that town. Well within my newly understood normal range. The same thing happened a few days later at another mountain pass town where I shut it off. I just topped it off again when cold and kept driving. But, I was worried.
Fixing the ac, researching the transmission engine braking, researching and upgrading the brakes were first. Then I got around to coolant. I stumbled across this website that had a formula for how big the overflow tank needs to be;
https://blog.cantonracingproducts.com/blog/calculating-expansion-tank-size-requirements
My truck was projectile vomiting because it had a 1/2 gallon over flow tank when it needed at the minimum a gallon to 1.5 gallons. As I wrote above, I am just an idiot sometimes. Thankfully, people are making actual square body Chevy overflow tanks new again. The space between the Cold line and the Hot line is almost an entire gallon. All is well in my world now.
Oh, I couldn’t use a CUCV overflow tank of which I have several spares because of the battery mount on the drivers side and the turbo air filter on the passenger side.
Hopefully, someone can learn from my mistakes.