Low Vacuum and overheating

[Andrew]

I'm posting this for a friend:

He's got a 68 GTX 727 auto with a low miles rebuild 440.

It has a very mild cam and a 6 pack. Compression is around 190 per cyllinder if I remember correctly. Cant recall leakdown test #s but the only issue was the crank case. He did break the motor in with synthetic oil, so maybe the rigs did not seat. He's trying to put some miles on it with break in oil now- not sure if it's too late.

The intersting thing to me is that the car can sit at idle for 45 minutes at 140 degrees. When he drives it is when it shoots up over 200.

Also the vacuum is around 8" at idle. tried spraying the intake etc. - nothing.

 

[70rr-brian]

8" seems pretty low for something with a mild cam. Is it steady on the gauge or jumping around? To verify rings being a problem with just a compression test you can do the test normally...then repeat the test on each cylinder after spraying oil into the cylinders. If the compression numbers are better after misting with oil then it is a ring problem. But the leakdown could provide similar info assuming the air isn't leaking out of the valves somewhere.

Are you sure the air/fuel mix is right? May be running too lean which could cause temps to climb. Also could contribute to low vacuum reading. Although probably not that much. Could be timing as well. Could also be lower radiator hose collapsing when he is driving causing the temp to climb. Could also be an air pocket in the cooling system somewhere.

So many things could be going on here it just hard to say.

 

[Andrew]

Yeah it's been driving him nuts. The vacuum guage is teady, but I'll pass some of your suggestions to him thanks.