overheating problem

[Scooter67]

I got a 4.3 CPI v6 in the '67 and it wasn't two miles outta the driveway this morning and darn temp gauge is sky-high. Parked for 30 mins, then drove back and it hovered near the full hot mark all the way back.

Once home with engine idling, it came down to 180 and sat there fine. Then rev it up, let it sit about 1200 rpm and temp guage climbs and climbs, way up to the hot mark.

Thermostat is opening, radiator is hot, electric fan comes on, so I dunno what's going on, unless the therm isn't opening all the way. Any guesses?

[cdowns]

what type of belt system are you using?? most 4.3 are set for serpintine belts and if you're using a conventional pulley and belt system the water pump will turn in the wrong direction

[Scooter67]

It's got v-belts. PO addressed the wrong-direction issue and told me which water pump to get if this one ever goes out. Don't remember which one, but I got it written down at home.

[67ChevyRedneck]

Maybe the gage is broken??

[Scooter67]

I'm hoping it's the therm not opening all the way. Gauge climbs and falls, so I don't see how it could be bad although I thought that at first.

Thing that bothers me is how fast the temp climbed. Usually takes about 3 miles before the gauge climbs to around 190, then you can see the needle fall as soon as the thermostat opens up. But today I wasn't a mile down the road before I noticed it was climbing way higher than that.

[67ChevyRedneck]

I had a toyota that did that once.... turns out I needed a new radiator. Are you running dex-cool or the green stuff?? Don't know if you know or not, but you CAN NOT mix the two. Has to be one or the other

BTW: That's a cool set-up. What kind of fuel mileage are you getting, and does the truck have good power?

[Scooter67]

Been using green coolant exclusively for almost a year now. Installed a new rad last month. If PO had been using Dex, then I added some green, what would happen? I've never seen any signs of clogging or anything.

Thanks for the compliment. If I didn't know better I'd think it has a v8. Really quick off the line up to about 50, beyond that it's more like a regular car and will drop down outta overdrive before there's lotsa passing power. Gets about 15.5 city, 18.7 hwy with 3.73 gears

[Johns70]

thats really good milage just imagine if you had 3.54 gears or even 3.07's

[chevykid04]

could be the thermostat, not opening properly, even new ones have been known to fail, there really cheap, its good insurance, and youll have an extra one if it aint the prob, but about a year ago, i had overheating probs, and had just gotten a new radiator, turns out it was a bad cap blowing fluid out and then being really low on fluid, bought a new rad cap, filled fluid, prob fixed... could also not be in your cooling system.... check your oil level, color and smell, see if anything strange is going on

[67ChevyRedneck]

Good suggestion, forgot about a head gasket problem. Check your oil to see if you've got some chocolate milk in there. The chevy engines with dex cool have had problems since the late 90's with head gaskets. Good motors, but you can usually expect to change the head gasket at least once. The problems I have heard about dexcool mixed with green is that it can cuase the dex cool to solidify and plug up the radiator. I read that info on the gm-trucks.com message boards. I tried to find the threads I had read for you, but their search function is down. Hope you figure out the problem!

[Scooter67]

Good news, the oil is nice and clear. Only had time to remove the thermostat and go get a new one last night. Should be able to get it installed and check it out tonight.

If that don't fix it, think I'm gonna check the the temp sender on the engine, maybe the dash gauge, and convince myself there's no way an electrical malf could cause the gauge to rise and fall with rpm.

[Scooter67]

Replaced the thermostat, now she's working fine. Seems to open sooner and more gradually than the old one, which would let the temp get pretty high then open all of a sudden and you'd see the needle drop like a rock. Now the temp stays more consistent, and lower too.