I installed a 97 crate motor in my 93 Z28. Filled the system and bled the air out. For some reason the cooling system is getting a ton of air in it. I did a compression check on it and this was the results Cylinders 3,2,4,6,8 were 190 PSI, Cylinders 1,5 were 200 PSI, Cylinder 7 was 183 PSI. The test was run with all of the spark plugs out and the block was warm. None of the plugs showed sign of coolant on them. If I run the car with the radiator cap off you can definately see the large bubbles coming out. If I leave the cap on eventualy it starts leaking out the cap after a little while (10-15 mins) of sitting idling. I am leaning towards a head gasket leak, but first was there a difference in the cooling system between 93 & 97 LT1's? Also it seems a little strange that the pressure is so high on #7 (13.5% actual loss from highest PSI where 30 % is the max according to spec) to have a large leak in it. Anybody want to steer me in a different direction before I tear this new motor apart? Thanks for any help.

 

Your rings haven't seated,if there were 50lbs difference i would worry and cooling system is not bled.Does your thermostat have a small hole in it to bleed the air trapped behind it.Do you have the air bleed's for the cooling system hooked up,is the cross over line in back of the heads hooked up.It is normal for a full radiator to expand and push some water into the overflow.Make sure all the air is out with the cap off.It will belch a bunch of water when the ts opens.Refill slowly and see,it should be fine.Otherwise use the bleaders and let it run until you get water to come out then uncap and refill.

 

It constanly overflows with the cap off, one thing though. The old motor had and oil cooler on it but the pipes were corroded almost all the way through so I didn't put it on the new motor. The new motor was complete ( Intake, wp, dist, wires, everything) and I got a new tune from alvin for the difference in injectors. I bypassed the oil cooler cooling lines from the water pump straight to the radiator. I wonder if that is causing some type of havoc on it? I replaced the thermostat yesterday before I did the compression check and it didn't seem to make a difference. I am going to try and bleed it out again. Only 1 problem though the one hose bleeder is higher than the radiator and I will bleed it a little bit but the rest has to be done with the motor running. Thanks for your help, maybe this will shine a little more light on the subject.

 

The oil coller being removed won't hurt it.Go to the parts store and get the correct size rubber caps to block off the oil coller water fittings that may be your problem.The pump is pumping direct to the radiator if your jumper is from the pump to the rad. Before you do take a pair of vise grips and clamp your oil cooler bypass line and see if it makes a difference.

 

my 95 does the same exact thing. i can fill it up and drive it for about 2 weeks then the low coolant light comes one. i fill it up while its running, bleed the system, then shut the car off and some coolant just comes out the overflow, taking taking me back to the point that i basically started at. i have done a compression check, leak down test, replaced radiator cap, car has new water pump, new thermostat, and i still has the same problem. i removed the inner parts of the thermostat the other day to rule that out, and now waiting to see the results. i talked to some friends and they suggested that i might have an obstruction in my radiator. so if the thermostat doesnt fix the situation then i will probably pull the radiator out and test it. ill let you know if i figure out what my problem is because it sounds like we are having the same issue.

 

i am also having an over heating problem,

this is more for firetird tho

I havnt checked this my self but some has just told me that old radiator hose will colape on there selfs when you hit gas and the pump pulls the water thru the pipes (if the are soft the sucktion will make them clost you know what i mean!

just something else to check that i didnt see post here anywhere

 

yep, checked that already but appreciate all the help.

 

Never had any cooling problems before the new motor, only a few broken rings . I will try the plugging of the hoses tonight after I get all the plugs back in. Thanks for your help on this.

 

Plugged the hoses off and it stopped overflowing and cooled correctly again. A simple fix that I have stared at for a month now. What a pain in the butt.

One last problem though, what was the correct idles speed with a load on a LT1? Mine idles at 1500 and I can't back off the adjuster anymore without setting a TPS code. Maybe a vacuum leak from where I plugged off the EGR and Air pump lines on the back of the intake? Already got a new tune from Alvin on the motor so I am going to rule that one out.