I own a 1993 Chevy S-10, 2WD, 4.3L 262CI V6 FI VIN:Z, 152,K miles. The truck is experiencing, what seems to me, an unusual high amount of pressure in the cooling system. It's very noticeable in upper rad hose, visible by over expansion. Hose becomes swollen and very firm. I understand that cooling systems build pressure but I've always been able to squeeze the hose together while running at operating temp. This problem occurred 2-3 months ago. I noticed because it started losing a little coolant over a 3-5 day period (maybe 1/2 a liter). I have personally replaced the water pump (second pump in 10 months), upper and lower rad hoses, thermostat (twice), and rad cap. I don't believe the water pump was bad but tried it just in case, along with thermostat. The upper rad hose was replaced around the same time I changed the first water pump. I tried T-stat first (no difference), then second water pump ( no difference), then rad cap ( no difference) and finally had a mechanic run a test to check head gasket (supposed to be fine). I was told the upper rad hose was bad and had them replace it, still building pressure and is visible in upper rad hose along with moderate coolant loss. No noticeable overheating. The radiator is 18 months old, replaced new after I bought the truck because the one it had was leaking in several places. Is this pressure normal? What should I do? Thanks for your time.
I also run a lower temp thermostat. I remember one time many years ago when I got 4 thermostats in a row that were bad. Must have been made on a Monday morning or a Friday afternoon. Hope you find the problem. One more thing. When my temp sending unit got old and crudded up, the gauge always ran cold. I took it out and cleaned it up on a wire wheel, reinstalled it and the gauge came right up to normal temp. Worth a try. Even a new temp sending unit isn't that much money for the peace of mind you'd get from a correct reading gauge.
Check for a blown head gasket using one of the kits that Scotty has talked about in his videos.
https://www.amazon.com/Block-Tester-BT-500-Combustion-Leak/dp/B06VVBSFTF
Sounds like a bad thermostat or the overflow tube from the radiator to the overflow tank is blocked. Make sure you burped all the air out of the system by turning heat on HIGH and running it. Could be air trapped in the system
Thanks Doc. The mechanic shop I took it to used that exact type of system to test for any leaks and it came back as a negative. The shop seems to be an honest one from what I've encountered from them. I was talking to a guy just yesterday who owns an later model S-10 than mine but with the exact same engine and he said it's normal for the hose to be expanded like that as the coolant is circulating. I tired two different methods of burping and no air bubbles or pockets came out so I don't think that's a problem. Thermostat is three weeks old and so was the one before that. I normally only buy the best parts and don't really want to pay for another $12-15 T-stat. Like I stated, it runs fine and no noticeable overheating. I'm running a 180°F now down from the recommended 195°F. To be completely honest I'm not positive the T-stat was bad in the first place but it is what it is. Wish I'd have gotten into mechanics at a younger age. Thanks for your time.