So I've got my new GMPP 350 290hp crate engine in the car and running quite nicely, and I've really just been putting as many miles as I can on it to break it in, but for the past couple days I've noticed something strange.

From day one, I've totalled about 5 gallons of coolant (1/2 and 1/2 mix) in the whole system. At first, I filled the radiator full, and then allowed it to go into the motor once the thermostat opened, and then topped off the radiator again (which was not 5 gallons totalled). It ran a little hot, around 200, so one day I didn't have enough time to let the engine cool so I could remove the radiator cap, so I just filled up the overflow tank with more 1/2 and 1/2, and it was all sucked in by the end of the night. I filled it up again, and it pulled about 85% of the container in, and there's a little bit in the bottom of the container now.

The strange thing is, since I filled up the container the 2nd time, it's been running unusually cool, in the 150-160 range. It's a 190 degree thermostat, which I was going to change out for a 180, but I don't see the need to now.

I have 2 questions:
1: Is almost 5 gallons an unusual amount of coolant to run in a system?

2: Is it bad that it's running so cool? The temperatures have been in the 70's, so it's not like it's that cold outside.

I don't mind it running cool, but it just seems kind of unusual. I guess the possibilty of the gauge being bad is there, but it's always been accurate before, and it still seems to be functioning properly.

 

I would put in a 180 stat, that way you can see if your old one is stuck open. You want it running hotter than that especially breaking in a motor. Are you sure you dont have a coolant leak once the system pressures up? Good luck!!

 

I have the same engine (GM Performance 350/290) in my '75 and I too noticed it runs cool....I have installed a 180* thermostat and it runs around 160*...when I had the stock 350 with the 180* thermostat, it ran at 180-190*..I checked the sending unit and it is the correct one (same one out of the old engine)...so I am curious to hear what the forum has to say.

 

Your system should take about 21 QTS...

 

Well I guess I'm good with the amount of coolant. I'll try the 180* thermostat tonight and see what difference that makes.

 

did you let the air get out of the system when filling up ?

 

Call me stupid, but how exactly do you manage that? I filled up the radiator to the top and then put the cap on. The cap's higher than the rest of the system, so should it matter?

 

Was this the way you filled the cooling system on the initial startup of the brand new engine?

 

This really sounds like the problem with the temp is either your old t Stat is stuck open (thankfully not closed) or your temp sending unit is going bad.