10er

The other day I came home from running around town doing chores and heard some strange sounds coming from the engine bay. It appeared to be the coolant boiling although I didn't open the expansion chamber cap to look inside, thinking it might just puke out if I did. I checked the Temp Gauge and it was up around 215, but not even close to the red zone. I let it cool down for a while and came back later to check things out. I didn't see any leaks and the coolant level was midway between the cold and hot marks, so I don't think any was lost anywhere. I haven't driven it since, so I don't know if it was just a fluke, or a failure of something like the Thermostat. I replaced the radiator maybe 10k ago with an Al unit, and the truck has been running near the bottom of the gauge since then until this incident.

My first question is what should I check in the system?

Suspecting the Thermostat might be the problem, I found there are two different ones available: a 195 F unit (the standard) and a 180 F. Why should I choose one over the other, if I have to replace the T-stat?

tech2

use the standard thermostat...running a cold engine encourages sludge build up...water and oil = sludge.
when its cold, open the rad and check the level in the rad....is it low?
Is the rad cap sealing the system...if its not, the cooling system can boil over at 212*F

10er

Thanks, tech2. I checked the rad cap and found it was almost 1/4 turn loose on the radiator. Not sure if that would be loose enough to allow pressure to escape and let the system boil without puking out, but the rad was full and the coolant tank was at the cold level. The upper rad hose seems to have juice in it as I could hear a sloshing sound in the radiator when I squeezed it. However, the liquid in the system was a very rusty color and obviously in need of flushing. I'll get started on that before I go down any other roads right now.

I've been looking into coolant, and it seems like there are three kinds: the standard ethylene-glycol based stuff (green color), Chevy's DEXCOOL silicate-free brand (orange color), and PEAK brand (color unknown). My Chilton manual warns not to mix the green and the orange because the green stuff will ruin the "better performing" orange stuff. Then the PEAK stuff claims to be compatible with both of the other types, even though it appears to be ethylene-glycol based, and claims to last longer than the orange stuff. Any thoughts on mixing the orange and green stuff, and if the PEAK claims have any value? I'm just thinking about topping up in the future, as the system will have a uniform fluid in it after the flush. Or am I just going down an empty rabbit hole?

tech2

no sure what year you have. green mixed with orange turns the long life; well its now a 2 year coolant. if your not going to completely flush out all the old coolant....stay with the green.

10er

It's a 96 w/ LN-2. I took a chance and drove it around today since all the fluids were topped off. It ran just fine, and the temp reading never got close to the boiling point, so I guess the slightly loose cap was what caused the problem. I still plan to do a the full flush and fluid replacement soon, so I appreciate the thoughts on green vs orange. I read that orange (specifically DEX-COOL) caused gasket failures because of an inhibitor it used, but GM claims the problem was caused by running for a long time with low coolant levels. Go figger... I'll probably stick with the green stuff.

Thanks for your help!

tech2

if dexcool is left in to long it becomes acidic and the plastic gaskets don't like it. change it when its due and you won't have a problem. If you ever replace the manifold gaskets...go with a steel frame design...not plastic.