d4 5t radiator surge

Lots of those D4400's have been converted to direct electric start without cooling issues. If there is no sign of air bubbles or boiling temperatures, I would suspect a restriction in the water circulation either from a malfunctioning thermostat or water pump issues. Did you rebuild the water pump along with your other work? Get one of those infra-red remote reading thermometers and go over the system operating temperatures.

Does it have a pipe that goes from the thermostat housing to the water to by pass flow the water when the thermostat is shut it might be rusted and blocked maybe ???
If it cools fine when the thermostat is open I would think the pump is ok
And you know the thermostats are working fine and shutting off ok but it sounds like the water has no where to go to me

Paul

just a couple of weeks ago, after the radiator was rodded out with no thermostat in place, the temp gauge would not move off the bottom, and engine would not warm up enough to run smoothly, so new cat thermostat / regulator was installed, new gaskets / o ring as well .. when it gets up to [gauge indicated] 140 to 160 F, the surging starts, no bubbles, just the level going slowly up and down, around 5 seconds to go up, same to go down .. water pump was not rebuilt recently.. but seemed to work fine without thermostat, gauge does not go higher than 180 [standing, appx 2/3 throttle], it's not boiling at all, there is no externally visible water bypass pipe, the thermostat is right at the very top of the casting maybe one inch away from where it bolts to the top radiator casting .. will be going out to the farm today again, and let it warm up a bit and give it the first oil change since rebuilt, only maybe three hours on it so far, but the rebuild was an inframe, and figure a $50 pail of oil is cheap insurance.. not sure if the surging is an air lock or just the thermostat opening and closing, water level is only 1/2 inch below top of rad ...i "think" i may have a non contact thermomter someplace, will try to find it and take it with me.. thanks

From your description of the coolant "surging" I'd take a guess and say there's some air trapped in the system somewhere. If you have a hill, climb it and when you get to the top, check the coolant level. If it's down from usual, add 'til it's up to where it should be.

When I change thermostats, if there's not a small bleed hole in the plate I drill a 1/8" hole. That lets air in the engine bleed out as the radiator is refilled. The last two thermostats I got from Cat did NOT have the air bleed hole in 'em.

I was going to mention the 1/8" bleed hole but ol Grump beat me to it.
You can also use the automotive type simple thermostat and do the same bleed hole thing. I'd have to go dig around for the part number but it is a standard large flange regular automotive type that fits nicely into the radiator pipe neck flange.

I'd be interested in that Part Number also!

I'd be interested in that Part Number also!