Dan Marino

I made a custom coolant bypass system for my truck. I made it and installed it over two years ago and it works well. I mainly put it on the truck for sled pulling but recently I have used it if I know I am going to pull a steep grade or if I have the truck loaded with something.

For some reason my truck gets hot easily and has for years. I have replaced the thermostat but it climbs above 200 and goes to 220 way to easily - so I started cracking the coolant bypass to help keep it cooler.

My question is related to the relation the oil pressure has to when the coolant bypass is open. The oil pressure climbs high when I have the bypass open when I drive. When I close the bypass the oil pressure returns to normal - Can somone explain why it does that?

AH64ID

I would guess the bypass is making the oil cooler more effective, and they colder oil makes for more pressure.

Same is true in the opposite. I can start a grade at 2K rpms, pull it at 1200-1250° EGT's and coolant at 215°, oil pressure starts at 58 and ends about 50.

That is all assuming your looking at a real oil psi gauge, and not the one on the dash.

Lastly, the OEM 190° thermostats don't go full open until 207°, and have a max allowed temp of 225°. With my modest 400 rwhp a full load at 2K rpms will get me about 213-215°, but 2300 has a hard time breaking 207°.

Dan Marino

hmm makes sense on colder oil. the problem I have with my truck is that it hits 220 and higher unloaded. Cruising at 65 to 70 I can keep 190-195 easily. If I kick it down and hit high RPMS or speed it climbs way to quick and then stays hot. I dont know