I have a '91 Z28 that has a carbed 350 in it. It had sat a while, but put a new holley on it and it ran great for almost a month. All of a sudden it started overheating. The radiator cap is holding pressure, could definitely tell that when i opened it. Looks like the water pump is pumping, because i can see plenty of coolant flowing. The thermostat opened, cause i could feel the heat on the upper hose. Also just took it out and boiled it to watch it open. Both fans are wired to come on with the key. What am I missing?

 

Did you use a gasket sealer on the new carb? I'm positive it has something to do with the new holley.

 

I had a shop install the carb cause i didn't have the time witha all the other projects going on. It ran for about a month after install. You saying they might not have used gasket sealer and it is causing a leak?
Oh, forgot to mention I do have the air dam installed, but it's overheating sitting in the driveway anyway.

 

I don't have a carb, but I've been told you aren't supposed to use gasket sealer, because it messes with the heat transfer. I would take it back by the shop that did it and have them look at it, and then get a second opinion from a different shop.

 

Maybe you're a victim of the heatwave over there of late, been a lot of these threads lately.

If all the parts are good (rad cap, hoses, pump, rad not blocked etc etc), you have coolant flowing under pressure, timing is not retarded, and mix is not lean then generally:

Overheat at highway speeds = air dam.
Overheat at low speeds or idle = lack of air flow across rad core. Ie fans and shrouds.

 

Yeah.. I think I found the problem. Looks like one of my fan mounts broke. One side of the fan is kicked back about an inch and a half from where it should be. Guess I'll have to get under there and fabricate a new mount and give that a try. Gonna have to wait till next weekend though.

 

Do you have dual electric fans? one of my lower mounts broke and I tied it to the sway bar with some fishing line. It works.

 

Yeah, that's what i have. The lower passenger side mount broke. I'm guessing that mixed with the 100+ degree heat here is too much.

 

That's probably enough for it to be sucking in some hot underhood air from the sides, instead of from the rad core.

 

Figured I'd update since I finally fixed my "overheating" problem. After spending around $200 on miscellaneous parts (thermostat, radiator, coolant, etc.), I used an IR thermometer, and seen my coolant was around 170 while my gauge was reading 230. Swapped to a new temperature gauge and it sits steady around 180. Never seen a mechanical temp gauge read high like that. Haven't fully removed it to inspect the tube, but figured it would have read low or nothing if it was kinked or punctured. Oh well, I can drive it again. At least until I sell it.

 

The stock guages are notorious for providing inaccurate readings.

 

This was an aftermarket equus gauge with the bourdon tube. Switched to aftermarket gauges after I switched to a carb. Never seen one of these gauges go bad.