Cooling system under performing
 

I have a freshly rebuilt '75 360 in an '83 d150. It's past the initial break-in and runs great. The issues is that the engine doesn't seem to heat up properly. I can drive it all day and the gauge never get past the second mark (not even 1/4 of the gauge), where it used to sit at the center prior to the rebuild. It has a stock replacement water pump, stock rad that was in the truck (originally a 318 non a/c), and a new thermostat (a 195 I think....), the rad and overflow are both filled properly with fresh coolant. I'm thinking the thermostat is stuck open, but would like input before I drain and rip it apart while its -28*c out there.
Thanks!

well if its -28C where you are thats pretty dam cold man no wonder it doesnt get up there! my 87 never reaches above the second line on the gauge and it makes me nervous when it creeps just above that ive got a new thermostat too and thought that two lines was normal?

Well, I finished and dropped the engine in in the early fall, had a few days at 10-15* c, and still sat at the second line, when it sat at center for two years before the rebuild. I have to get it going and take out all the Xmas recycling stuff tomorrow before the bins fill up, hopefully it'll put some heat out, the heater did seem a bit week the last time I had it out.

Is this the same engine that was in there when gauge sat at the center before?
Usually they hot tank engine prior to machining on a rebuild to clean all the garbage out of the oil and coolant passages.
Which means your cooling system might be working the the way it's suppose to.
Try covering half the radiator with cardboard to see if that helps.

Dave

Yes it is, though it's not original to the truck. When I used it the other day there was Bart any heat (not enough to defrost the windshield), I'll block it off some next time and see where that gets me.

I covered all but top 6 inches of my radiator and it did not reach operating temp. today (11 degrees F) I do have warm air tho.
I will cover more till it gets there.

Dave

Is the thermostat one of those "fail safe" ones? My experience with them is that they get stuck open and won't allow the engine to get up to operating temp. I switched back to regular style T-stat.

Yeah, it is the fail safe type. Seemed like a good idea at the time. Once or warms up (been in the -30's this last week!), I'll probably change it out.