Well, we finally got my car back together again, after replacing the head gaskets in hope that that was what was wrong with my car.. and it still overheats.

We've got the timing locked in right where it needs to be, had the radiator checked over and it works, replaced the thermostat, hoses are good. We got the air out of the system, and made sure the water pump works, so those aren't the reason...

I'm starting to get royally pissed off at this thing. It starts and runs really well, but within a few minutes of driving, it'll shoot up to 220+ degrees, and it'll go above 250 if I let it.

Anybody have any suggestions, before I decide to sell this thing out of desperation?

This is in my '79 Z, btw

 

I hate to say this my friend, but it almost sounds to me like one of your heads is cracked.

The stock thermo-clutch fan, shroud, and radiator do a fantastic job of cooling in the Z/28. In fact as an illustration, my buddy put a 160 thermostat in his '81 Z28, and even in the summer the engine actually ran too cool, so he put a 180 stat back in.

When you had your heads off, it would have been a good idea to have taken them into a shop and have them pressure checked. Late 1970's and early '80's 350 heads (ie, the 882 for example) are of the light-weight casting design, and prone to cracking.

In any case, that type of sky-high coolant temps usually indicates either a blown head gasket (which you have since recified) or possibly a cracked head. I certainly hope I'm wrong, but that is my suspicion.

Hate to be the bearer of bad news.

 

Heh, I guess I should have mentioned in the first post, that we just barely had a set of heads rebuilt specificly trying to fix this problem, and it still overheats. Whupsie, my mistake :P

This is also a freshly rebuilt engine, with not even 20 miles on it yet. It didn't used to overheat before the rebuild, so I'm starting to think that we might have screwed something up :x.

 

Well start with the basics. Check the thermostat, make sure it is opening. Feel both hoses, if the upper stays cool after 195degrees replace the Tstat. After that make sure you are not running lean. THEN do a pressure test of the cylinders. HOpefully its just a defunct Tstat (and dont try the "its a new Tsat" on me, Ive seen too many new ones not work).
Good Luck.
CoryM

 

check you radiator for corrision or build up if the coolant cant contact the metal in the radiator it cant cool down check the a/f ratio so it isn trunning lean check timing

 

Do you have any actual coolant in there? Water may be the best in heat transfer but it will boil quickly..Do you have the proper gaskets for the heads and intake? If you have a water jacket blocked off then your asking for trouble..When the engine was rebuilt you had the block fluxed didnt you?.....Check the deck surface as ive had a 350 block that was cracked somewhere and it burned coolant to the tune of a gallon aweek...Is teh rad big enough..Keep the rad cool with a water hose and fresh water on teh fins to help it dissapate heat while you stand still..An infared perometer is handy here..If you know a mech or HVAC tech they may have one you can use..

Any finally how are you checking teh temp...Hopefully not with an electrical gauge..That perometer comes in even hadier at this point...You should shoot it at the front head surface water pump inlet and out let as well as the block side near the freeze out plugs..

 

I may have talked to you today at work. I work at Summit and a guy called from Utah with the same problem. Like I said check to see if air flow has a path of least resistance around the radiator at speed, ( basicaly check if your airflow is going through the radiator NOT around it, like through an open seam between the top of the core support and the radiator ), also check to see if your lower air-dam is in place. Some f-bodies will overheat with a damaged or missing air dam.

One thing I forgot to ask if your lower radiator hose still had the spring inside, because a high flow water pump will suck it flat at higher rpms and constrict water flow. The spring is there to stop the hose from collapsing.

 

Checked to see if the spring is still in the lower radiator hose yet???

 

I'm with LT1form on this one. No spring in the lower hose and the water pump will suck it flat once the RPMs come up. Rapid overheat is the result. Give it a squeeze.

This one can give you a real head-scratcher of an overheat problem.

 

I own a '79 z and had a few problems too, mine was pump, then it was hoses collasping all over

1. Check for hose colapse. My Z28 likes to try to suck the hose closed. I had to get an upper and lower spring enforced hose.

2. Replace the radiator Cap. May sound retarded, did to me at first. I listened to the guy at AutoZone and it fixed my '78 Buick Lesabre Cop car. Plus it's a cheap fix. Radiator has to keep pressure to keep from over heating.

3. What degree thermostat did you use? I've heard of even drilling a few small holes to allow some coolant to flow before opening.

4. Is the pump circulating any fluid? May be a bad pump.

5. To Rich, To Lean gas mixture? I lucked out, my Hooker Headers had an Oxygen Sensor Bung, so I stuck one in and bought a cheap Gauge that hooks up to single wire Oxygen senors you can rip an Oxygen Sensor off about any new car at the junk yard, just pick one easy to get at.

6. Go electric fans, Frees up HP and you can get programmable thermo gauges to turn them on, or what I used a Moroso 160° thermostat switch to turn on fan(s). My 2nd fan is on all the time (need to rig a switch for winter) Highest temp was in traffic and it was 170°

For fans, if you are a cheap tight wad, like me ... My junkyard expereince is to gimp a Ford Taraus SHO fan. I made my own brackets and have two fans in my 79. Granted each fan's blades hangs over the radiator. Plus I had to redo the tranny lines. But, man do those fans pull air.

 

it sounds like a goofy mistake but check and see if you have your intake gaskets on correctly if you have the wrong ports covered it will cause the same problem

 

i just put new heads on , and the machine shop told me to drill 2 little holes in the base of the thermostat,so when you first start it, it gives the thermo a chance to open up.

i tried it and it worked fine.