tjctransport

91 S10 PICKUP 4.3 ENGINE, NO AC, 73,000 original miles.
this is my neighbors car, i am trying to fix it
the water pump was leaking last week. the daughters boyfriend put the new pump in.
took it out for a ride and she said it was fine.
sunday, the temp gauge spiked at 260 and CEL came on.
flushed engine, heater core, and put new thermostat in because the engine was full of rust. tried to flush rad, but the core was plugged with rust that was disturbed when the system was drained.
infrared temp gun on radiator told me rad was plugged.
ordered new rad and put it in with new thermostat, took for a ride and same thing. temp gauge spikes at 240-260 degrees.
shut it off for 1 minute, and gauge drops down to 180, then slowly climbs back up to 240-260
pulled t-stat, and temp gauge sits at 110-120.
yesterday i shot the block with infrared and got 180 at t-stat neck, 200-210 on head at temp sender. gauge was reading 240-260
today i put new temp sender in, still reading 240-260. but the engine temp sensor at t-stat reads 179 as per the scanner.
sitting in traffic, or driving down the road, it reads the same, 177-184.
so i know the truck is not overheating.
what i can not figure out is why the temp gauge spikes between 240-260

so to recap, everything was fine.
water pump started leaking, was changed and temp gauge started reading high.
the truck now has a new water pump, radiator, temp sending unit, and 180 degree t-stat with an air purge hole drilled in it.

anyone have any idea what is going on with this thing?

legotech7

I'm having the same exact issue with mine. Same engine, same year, did everything you mentioned in your post. The only thing I can think of is a faulty gauge at the cluster I had to order an after market one, and also ordered a gauge pod for it. When I get them in, I will post up details. In the mean time I have been checking my temps with an inferred temp gun, just to make sure everything is kosher.... Couldn't find an original temp gauge anywhere, so the after market will have to do. If you have resolved your issue, please post the details. I'm sure there are tons out there with the same issue that can benefit from the information, thanks.......

tjctransport

the problem ended up being an air pocket in the back of the engine.
i even changed the temp sensor in the block because i got high readings at the block but cool at the t-stat.
it took close to 2 weeks to get all the air out of the system.

legotech7

Well I did bleed the system, and I used one of those spill free funnel kits to make it a bit easier. Same thing though, cooler at the thermostat and a bit warmer on the block. But two weeks? Did you have to keep bleeding the system after your initial finding? How many times did you have to bleed it, and what are your temp reading now? Thanks for any help.......

tjctransport

it took just about two weeks to clear up. the truck only sees about 5 miles each way per day.
it bleed itself. and temp gauge now reads 160 degrees, because took out the 190 and put a 160 t-stat in it.

legotech7

So you replaced the thermostat with a 160 instead of the recommended 195? Does it run correctly, and how is your fuel economy? I think if I were to replace the thermostat, I'd put in a 180. Those 4.3's need to be at about 195 for them to run smoothly. You may want to check your timing to see if its off a bit. Mine purrs a smooth as a kitten, but that high temp worries me. Still going to replace the cluster gauge and if that doesn't work, I'll replace the thermo. Thanks for the info, I'll post again with the results.......

Erminio Spadino

You need the stock stat I belive its 190 could be 195 I have to look tomorrow. For the computer to work correctly it was designed to use that temp. To controll the chock and the fuel mixture