Anyone had this happen to them. I reconditioned the heads in my 72 end of this summer. I've just got it going again and used the same thermostat (180). When I start it up and it warms up the temp gage will go near the 250 mark then drop like a rock to operating temp of about 170 180. I thought it was a sticking thermostat so I just replaced it today and it's still doing the same thing. I ran it today with out the cap for about 20 minutes at idel and let the coolant go out and on the floor. I fiqured that would get rid of any air but still does the same thing. It only does it once and thats only at start up when cold then I can drive for a hour and it never jumps again. Whats going on does anyone know what I have created since redoing the heads.

mine does that too, but only to about 200 degrees. it makes sense, since the heads are hotter than the intake manifold where the thermostat is. once water flows, it all evens out. joe

I'd check the resistance in the current to the temp sending unit. Don't forget that the thermostat traps the coolant IN the block till it opens at temperature. Then it allows the coolant to flow thru the radiator to be cooled. There shouldn't be a spike and drop like that. Its an indication that somethings not right. You might also want to run it up to operating temp w/ the radiator cap off and check fluid w/ thermometer. Also make sure waterpump has good flow. Just a coulpe of ideas!

Thanks guys, I was talking to someone that told me to check that my coolant must be low. When I check it (at cold) the level in the tank was near the bottom. He told me to fill it up to 3/4's and should take care of the issue. Well it did and there wasn't a jump. The only thing is that since there is no recovery system in the 72's it then pisses out on the driveway and I'm back to stage one. I don't remember it being this bad before. Why when the tank is low would the temp jump up like that, the rad is still full and the flow would still be there. Also is there anyone who put a recovery system in place in these old years. If so what did ya do...

My '70 has an expansion tank (passenger side of the engine compartment) on it so I think you'd be able to install one on yours without any problems. If you didn't want to go the metal expansion tank route I'd think any recovery tank kit available at most auto part stores would do the job.

As far as the temp spike goes, think about this. When you shut down after a drive everything is warm. The thermostat is most likely open, or will open for a while once the coolant flow stops due to residual heat in the block. With the fluid level being low in the system it is going to find a balanced level between the radiator and the block. If the level is as low as you found it in the radiator that means it is also that low in the block. As things cool down the thermostat closes locking the lower coolant level in the block. So when you first fire up the engine it will heat up what coolant is in the block VERY quickly (hence the temp spike) before allowing the thermostat to open and let more coolant into the block. Then you have even less coolant in the radiator so when it does pass through there it really doesn't get much of a chance to cool down any before being pumped back into the block.

Make sense?