Im still tuning her in and got her on the highway today....wrapped her wide open and was probably doing between 85-95 for a minute or so (I say probably, speedo is inop), running at about 3800 rpm (3 speed and 3.73's, she spins high) and my temp gauge was going BONKERS! She would shoot to 230, drop to 205, shoot to 230 again....all very quickly. This was only happening when I was running her real hard, at top RPM's. A level cruising speed of about 75 would sit me comfortably at 195 degrees...but as soon as I got on her she started playing games again, 230, 205, 230.....

So heres what I know.....I was running way too much timing. I turned it down a bit and it seemed to help, but not alleviate the problem. ALL cooling components are new. Gauges are cheap sunpro model and the sensor is plugged into the passenger rear of the head. (a buddy told me I was going to get abnormally hot reading from that location????)

Before we even go there, coolant level is fine, no symptoms of head gasket problems. (nothing in oil)

So heres my question......whats going on? Am I still running to much timing? Is this normal for a standard 1 row radiator? She never ran this hot with the stock heads and cam...????

 

I think if it were me I might start there

 

what brand thermostat are you using? ive had issues with them sticking before using non name brand parts. they would work fine under normal conditions, but towing or playing and the temp would go all over the place, from 190-230-205 in about a 10 second period. is this what you are seeing?

 

Yes, thats about what its doing. It just shoots up to 230, comes down just as quick, shoots up again....but again, only when Im HOGGING on it at the very top end. Its a standard pep boys t-stat...but its the same one I was running last season with no issues. (It was replaced mid season last year, so its not all that old.) The Tstat is a 185, and under normal operating conditions she usually sits at 190 to 205. (But thats so far in the COOL weather)

nj85z28....all kidding aside....the gauge worked fine last season....can temp sensor just freak out above certain temps? Does my location (back of head vs top of intake manifold) have anything to do with it?

 

i would try swapping the t-stat first. at less than $10, it wouldnt be expensive to do. i would use something like a mr. gasket or another major brand.

on a side note, i run a 180* on my dd blazer. the gauage read close to 180 (between 155 and 210). then once i swapped to headers, i had to replace the sending unit because i broke the factory one. now the gauge is only reading around 155, when i know its not. so there is the possibility of the guage being screwy. if anything, go to the old stand by of a thermometer on the intake

 

The gauge reads perfectly normal under normal operating. It only goes bonkers when I really open it up......Unfortunately there isnt much of a way I can check the temp when Im runnin WOT on the highway. She seems to run just fine when the gauge goes loopy. The oil pressure also bounces a bit too, but that may just be from going from WOT to cruise back and forth....what could be causing this?

 

Scott it sounds to me like you still have some air in the system and or the coolant is a little low, so check it again, lol. I have the same gauge only mine attaches to the drivers side head. It reads dead accurate, except one time when I was losing coolant from my heater core. It wasn't over heating but it was low enough that the probe would go dry for a few seconds and the temp would shoot back up, then come back down.

What kind of fan are you running?

 

Huh, the air pocket thing makes sense......except for the fact that it only happens under the most extreme driving. I usually fill the block from the intake, then the radiator, then the overflow tank when I put em all back together. The level in the overflow tank hasnt changed. You think an air bubble could manifest itself this way, at high speeds only?? Whats the best way to ck for a bubble and get rid of it?

My fan is a solid aftermarket non clutch type. I ditched the flex fan....

 

Two things I can think of....
Are you running an el-cheapo water pump? It could be cavitating at the high rpm's, which would mean it's pumping water intermittently.
Do you have a fan shroud on? If not, all incoming air won't get pulled through the radiator like it wants to be.

 

The air dam too, if it's not in place it will overheat.