Hey guys, I'm new on here but I have an 89' IROC 5.7 that I just put a new motor in from west coast engines. The motor is basically a stock swap. I have the motor in and the car runs fine but it is overheating after only about 5 minutes of running. It has a new t-stat, the radiator is flowing coolant (top hose gets hot, bottom hose stays coolish), doesn't appear to be leaking coolant anywhere, I replaced a heater hose, it has a relatively new water pump (I am sure that it is the correct water pump for the serpentine belt system) and the timing has been set properly. I am hoping that there is an explanation other than the new motor I put in has leaking head gaskets. Any thoughts would be greatly appreciated.

 

These are things that I would look at. Doesn't cost anything but a few minutes of your time.

"....the radiator is flowing coolant (top hose gets hot, bottom hose stays coolish)...."

Have you run it with the cap off and actually seen the coolant flow out of the tubes? It should be a nice strong stream, not just a trickle. You'll definitely be able to tell when the thermostat opens and coolant starts flowing. Always be aware of where you put your face. Don't get burned.

When filling the cooling system it helps to leave the cap off and run the engine until the thermostat opens and closes a few times. This helps purge any air that is in the system.

"....it has a relatively new water pump (I am sure that it is the correct water pump for the serpentine belt system)...."

You don't mention where this water pump came from. Your old engine? From a friend? I would confirm that you have the correct pump. Checking the coolant flow by looking in the radiator filler neck (see above) should confirm this.

Is the thermostat facing the correct way? Just pull the hose off the water neck and peek inside. Yes, I once put one in backwards on a small Ford.

Did you do anything about the radiator? Replace it with a new one? Boil and rod the old one? The radiator may appear to be flowing coolant but it might be partially clogged.

Are your fans coming on?

 

And do you have an air dam? Does it overheat in traffic but not on the highway?

 

Leaking head gaskets ?????

Aside from that......

What do you consider overheating ?

Is the gage pegged out or just in the red.

If its the stock thermostat its a 195* and stock fan switch the fans will not come on until after that.

That's stock = crazy

Put a 180* thermostat in and a fan switch that comes on at 190* and you might have a fighting chance at keeping it cooler.

If you want to test that theory then put in the 180* thermostat and ground the wire going to the fan switch in the head.

That's just to get the fan to come on earlier than the stock setting.

Its just a test to see if that helps. If it does than a fan switch that comes on at 190* would be next.

 

Thanks for the input guys. I think it looks like head gaskets unfortunately. Its a brand new motor, so hopefully I get it warrantied.