I might have an overheating problem.

After its warmed up, you can watch the gauge jump to past 280 deg then come back down to 190 to 200 within a few seconds. Thought it might be an air pocket, but it only seems to do it once and then it goes back to normal. Also only while it is moving. Had a mechanic buddy burp the system and got a few air pockets out. The motor never seems hotter than normal. Could I have a bad gauge? Do I just need to burp it more?

The motor is a .040 over 350. The cooling system consists of an Edelbrock aluminum water pump and a big aluminum radiator. I've had it together for almost 5 years and never had a problem until maybe this last year. The car has been down for about 8 months. Just got it running last week and had forgot about this little problem. For the time being its my daily driver. Would like to get this annoyance stopped.

Sounds to me like a sticky thermostat. Easy fix if it is.

The thermostat is staying closed too long and then opening very suddenly which causes the peculiar guage readings. Replacing the thermostat will probably help but why don't you try the following repair which worked for me: drill a couple of 3/16 holes in the rim of the thermostat. The holes allow a bypass of the heated coolant before the thermostat opens and this eliminates the thermostat from banging open.

Mrapii is right about the holes in the rim of the thermostat, but since you must remove the thrmostat to drill the holes, why not just put in a new thermostat? It's less work and a new thermostat is less than $5.00 if memory serves me correctly.

The holes in the rim can work wonders when a heating problem resists all repair effforts and one gets desperate for a fix. I have seen as many as four holes in the rim.

Another thought: A faulty thermal clutch could also be the cause. I once had a thermal clutch that would not work well until it got quite hot, then it would kick in and cool the engine down. I finally solved the problem by replacing the clutch.

I think I forgot to mention that I'm running dual electric fans.

I've replaced the thermostat a while back. Think I might try drilling the holes on a new thermostat. Maybe that will take care of it.

Thanx guys.

Are you using the stock temperature gauge or an aftermarket one? Where is the temperature sensor mounted? I had those symptoms when I installed an aftermarket mechanical gauge and put the sensor in the thermostat housing. :oops:

The car is a conquista, so I don't have factory gauges. The temp gauge is an aftermarket. It is in the drivers side head.

Grant, I had the same problem with my ride. I have Autometer AutoLite gauges and my sending unit was in the drivers side head and the temp would go well above 240* before the thermostat opened up and would run hot all the time. I moved the sending unit into the thermostat housing and now it goes from around 140 and spikes up to around 210 real quick and then back down to 190.

Ok, I need someone's expertise. It takes about 17 minutes for my '95 Z28 LT1 to get to the middle bar which is about 210 degrees. When it starts to go up, the electric fans kick on at 226, which they should. It gets knocked back down to around the middle bar. Goes up again if I'm not really moving. If I'm moving it'l stay in about the same spot, but the fans aren't on, so, it's below 226. I got the system flushed and put a new thermostat. When they guy flushed it he said there was good waterflow, so, I guess the pump is good and I've haven't noticed a leak. I'm kinda desperate cause I'm going to St. Louis from Houston this Thursday. Thanks.

I can't believe the fans are set to come on at 226 degrees. That seems unreasonably high to me. Better find a way to get it cooler before driving any distance!

Well, the dealer said it should be running at 210 degrees during the summer. And the LT1 runs a little hot to keep emissions down.

I doubt that you have anything to worry about. If the thermostat control is a little off and the temp guage reads high it sounds like it is in the ballpark. There are ways to run the engine cooler, I think SLP makes a thermotat and control. I agree with you that running an engine that hot seems less than desirable.

If you have a good cooling system that will hold 15 pounds of pressure, It will not boil till it reaches 258 degrees F. Late model GM v8 engines need to operate around 200 to 210 degrees F, in order to get maximun power from them. So do not be afraid to let it run around 210F.

My Elko does the very same thing. when at runnng temp, the gauge runs up past ½ way and then out of the blue, it comes back down.

the Enging is a 305 and never boils over, and never seems hot???
puzzling problem???

H E L P H E L P H E L P H E L P H E L P..........
MAYBE I SHOULD BUY A RANCHARO INSTEAD, JUST KIDDING HA HA HA

While we're on the subject, my 69-75 350?(not sure exactly) has just been rebuilt. I put my aftermarket temp gauge in the intake manifold on the front top of the engine. I put a 160 temp thermo in it, should I switch it to a 195? Also, should the upper hose be so damn solid when it's hot? Never went up over 210 yet.(well, except for when the copper hose off of the heater core let go and filled my front passenger floor with 2-3 gallons of antifreeze)OOPS lmao
Dude, these guys know what they are talking about. And I hope your trip goes well in your Elco.
LATER
dug