Question about 3406B in my Freightliner

The 3406 motor fitted into trucks in the U.K. were fitted with a plastic style impellor in the water pump, this item was pressed on the shaft and was a cause of many problems to blacken the CAT name, the pump itself was modified many times there was even a V.H.S. tape sent out detailing the changes that would send an Elephant to sleep, so the first place to check is the pump followed by the coolers (heat exchangers) the cooling system is very simple to test with the aid of a heat (temp) gun pointed at the top side of the spin on oil filter.

Think id try a thermostat first as that is the esiest and cheapest. Jason

Experience would tell me to go for the water pump as TC says, its unlikely to be caused by the thermostat if the top hose is as hot as the thermostat housing, but this is where the infra-red thermometer comes in, it will save a fortune in troubleshooting time and cost.

Jason, the overheating of these motors can realy muck up a thick wallet (Pocket book), to realy sort the cooling side the thermostats might well need checking, the heat gun is 1 of many ways of checking them out, but the thermostats are fairly costly perhaps to costly to just change out, the water pump rebuild kit is moderately cheap and realy needs that eyeball check, in saying that I do like to do the boiling water test on thermostats, so once you start getting inside the lump, I would also strip out the coolers, the gasket kit is just a few coins, once checked you know its sound, I realy make every effort to sort running faults in a complete style and rarely find that I have pulled something to bits in a time wasted moment, there is always some good or betterment to be made from taking the time to look.

Thanks everyone, I took it apart this afternoon and sure enough the impeller is loose on the shaft. I guess now the question will be new or rebuilt.

Thanks everyone, I took it apart this afternoon and sure enough the impeller is loose on the shaft. I guess now the question will be new or rebuilt.

Hi JIM, I know its a little ways for you but you can call american crane in kc down by kemper arena. they sell cat parts for truck engines as well as your heavey equipment, and useually a lot cheaper, dont know why? might have the serial and arrangment number on the engine ready if you call. there # is 913-371-8585

You might want to try a Cat 'remanufactured' pump, the prices aren't bad, they are rebuilt to new specs and wil sometimes actually be a new pump.

New or rebuilt pump would depend on the price differenc if it was me if it wasn't much difference i would put new on. Somthing else while you have it a part check the clutch lining on your air fan mine had none left when i noticed my fan wasn't enguaging. It is easy to check while all of the belts and things are out of the way. Just a thought while you are in repair mode! Jason👍