turckster

Cracked head(s) or bad air compressor. Isolate the cooling system from the air compressor, run the engine and see if the system still builds pressure quickly. If it does the you have a cracked head or blown head gasket, most likely a cracked head(s). These heads do not tolerate excessive heat, if one is cracked our policy is to replace both heads. The obvious cracks will be between valves or between injector hole and valves, its the cracks you won't see that will get you-inside injector sleeve at the tip sealing area, inside or around a valve seat and so forth. With it building pressure so quick it should be obvious.
A head gasket is a possibility as well but with overheating it is usually a cracked head.

The oil psi sender is behind the speedo/tach in an aluminum block. The #4 line off the filter base runs through the cowl/firewall to this block then to the gauge. BTW, unplugging the coolant level sensor will activate the alarm. When the coolant resivior/tank is full the coolant completes the circuit, by unplugging it you open the circuit causing the kysor module to think the coolant is low. More often that not the coolant level sensor is the problem, scale builds on the coolant probe insulating it.

If the engine has steel roller lifters you can re-use all lifters but the one(s) that failed(of course), On the ceramic roller lifters, it was Mack policy(under warranty) that only the failed lifters were replaced. But with customer pay we pushed to replace them all, I do not trust used ceramic roller lifters. Your choice on this, it is expensive to replace all the lifters. Other than fresh gaskets and seals, you should be good to go.

The top relay(Relay #1) supplies voltage to fuses 16, 17, 18, 19, 26, 27, 28, 29, 31.
Next down relay(Relay#2) feeds fuses 20, 21, 22, 23, 24, 25, 30.
Relay#3 (next down) feeds fuses-40, 41, 42, 43
Relay #4 feeds fuses-44, 45, 46, 47
Fuse #40 is for the engine ecu
Now, having said that, make sure the ground relay is good. It may be popping open while cranking the engine. It is usually caused by a shorted/bad starter (pulling too much amperage). The either shot spins the engine faster and the starter is barely pulling any amperage,so the ground relay stays engaged. A quick way to tell is to install a heavy gauge jumper on the ground relay studs, if the engine starts--there you go.