350 SBC ,small cam, AFB, 250 hp ,you know that engine . Always ran cool at 170* for 11,000 miles even with A/C on. 10 miles from the hotel it hits 250* . Change water pump and stat,at hotel, no help , towed home. Every thing that can cause this cooling problem it’s NOT doing. Please give me some cooling info !!!
So from your note,it was OK,then over heating. You put new stat*,if new one is good,an its not got any leaks,, My guess would be head gasket. But if idel is screwed up> intake leak can run hot from too lean. Another check,,Keep cap off,start,and look for bubbles in rad.? Cly PSI test could be a good check too. Timing got off/moved?
We need more details. If it cooled with no issues for 11,000 miles, the first question I would ask is: What did you change at 11,001 miles? If the answer to that question is nothing, then we must assume that some component failed. Start with the easy stuff. Is the gauge accurate at 250 deg's? It should be puking boiling coolant out onto the ground at that point, was it? If yes, what were you doing when it started pushing coolant (idling, driving, racing, towing, mudding, or something else)? If it is getting up to 250 idling or even just normal road driving, I would start to think about the possibility of a head gasket failure or a crack in a cylinder head? What other symptoms is it displaying? Your statement about everything that can cause a cooling problem it's NOT doing gives us no specific details to help diagnose. More info please.
Did compression check, all cylinders within 12 pounds,,, did pressure check on system , holds pressure, no leaks , new 10 # cap removed stat for now ,dry tail pipes,no steam. 11,000 miles on a new walker radiator, had just bought gas ,and was driving at 75 mph to the hotel and she went hot ???
Running hot just at speed? Or at idle too? Electric fan or mechanical? If mechanical, clutch or no clutch?
They didn’t give you a reverse rotation water pump by mistake did they? Wondering why you changed the water pump. If they’re not leaking they won’t cause an overheating problem. I did see one time 40 years ago when the impeller came loose from the shaft but it is extremely rare
Changed pump just in case the impeller came loose ,, it didn’t ! Checked for combustion gas in coolant ,twice ,, it ain’t got none . 5 blade mechanical fan with aluminum shroud, it has stainless spring in lower hose, runs hot fast or slow , now that it has a cooling problem.somebody’s got to know why ?
Maybe they sold you a reverse rotation pump. If your car has v belts and the car the water pump is meant for has a serpentine belt then the rotation is wrong. Let’s say your car overheated because of the thermostat, now you could possibly have the wrong water pump
Did you test the old thermostat? Just to rule that out as the cause? Check timing and both mech and vac advance is working?
You need cooling, baby I'm not fooling. Have you checked the timing? Maybe the distributor slipped, or the advance took a crap.
As has been asked and not answered is the only thing you are using to diagnose overheating the gauge? Have you used an infrared thermometer to verify it is correct?
The only thing I’ve ever seen that made one run instant hot like that and all the Normal go to items checked good was a distributor that the advance mechanism hung and sent the timing into la la mode. I gave a new unmentioned brand distributor away at the track one time because of it. Put my old back in and all was well. means nothing with out checking it for sure.
I use to get this all the time when I was in auto parts. “I need a water pump for a sbc” ok what year? “It doesn’t matter they are all the same”. Someone at the counter that doesn’t know the change over year or bothers to ask and just scrolls to the closest year in the computer. A reserve rotation water pump.
I'd go with a failed temp gauge sender. It happens suddenly. No amount of parts swapping will fix it. Replace the sender. What gauges are you running?
Did your radiator burp tank blow? Please let us know. If it didn't, you weren't at 250°. And then you can easily figure it out. Clue: somebody has already suggested the answer. If it did, and you had a 10 lb radiator cap it should boil over at 240° F.
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