Hi Thanks ahead of time for any help you can give. I have a 300 big cam and replaced the low flow raditor with a high flow and we changed the tank, but not the dual thermostats. It ran ok but would heat up by the time I got to the top of a hill. I hear I am supposed to change the thermostat housing to a single. Does anyone know this to be true an where to look for the parts I need? I have been making do, downshifting on hill etc, but yesterday it started overheating as soon at I put a load on it, I m thinking a therostat may have stuck and want to fix it right this time.

Bob

The low flow cooling system uses a "two pass" radiator which means the coolant passes through twice & not just top to bottom like conventional cooling systems. The rear thermostat stays open when the engine is cool to return the coolant to the oil cooler & block to help with a fast warm up. The front thermostat is closed during warm up & opens when the engine temperature rises. As the engine warms up the rear thermostat closes to route coolant through the radiator. If the rear thermostat isn't closing or if it is removed the engine will overheat quickly. Cummins had the low flow system working until they changed the thermostats from brass to plastic (some bean counter found a way to save a few pennies). When the plastic thermostats started breaking after just a few miles & they had to replace the scuffed cylinders they went back to brass. By this time customers were fed up with cooling system problems & Cummins had to go back to a single thermostat, single pass radiator to get customers back.
The low flow system was a good when everything was right. I still think that it was a good idea & would have worked if not for the plastic thermostats.
You didn't say why you changed the radiator. Was it overheating before the change?

thanks, that good info, so I should look for the rear thermostat an make sure it is closing. Yes my trk was overheating, so when I needed a new core I switched to the high flow core per advise from locals. I have since read there is more to the swith than what I did, ie, i need to change the thermostat housing. I am researching this before I tear it open this morning for the cause of a new overheating issue yesterday. For some reason it started overheating yesterday without a hill, an would cool down as soon as I idled for a while, which I think means the water pump must be ok, an I should look for other problems

Did the engine start overheating suddenly or gradually get worse over a period of time? I have seen Cummins water pump impellers get loose & slip on the shaft when the engine gets warm. The impeller is pressed on the shaft. The thermostats are in the same housing if you are looking for the thermostat.
I have never tried a standard radiator with low flow cooling systems. The hoses should have been different sizes.

thanks DMC Doc, I ran two loads in the morning and then the third load it overheated. It was a sudden thing to answer your question. I sat for about an hour getting loaded then when I left it got hot in a hurry.

I took out the thermostats today and am checking them to make sure they are working. Everything I looked at looked good, oil and water levels were right, belt was tight, so I am wondering if that water pump did just quit? Strange.

I found out today, that in switching to a high flow system like I did with the radiator core I need to change the water manifolds as well as the thermostat housing, an then I shouldn't have any permanent heating problem like I have had. I only run local and have been gearing down on hills. This is separate from the overheating i experienced yesterday.

Now I just need help if anyone knows how to figure it out exactly how the water flow needs to change and how to find my parts. I saw this information first on a forum thread last year and have been unable to find it again with any searches I have done. Appreciate if anyone knows how to do this or can steer me to someone who does. Thanks loads, Bob