Hi all, I am reassembling my D2 after a lengthy battle with the cylinder head problems. Getting to the final items. I am getting ready to set the thermostat housing in place. I noticed a large amount of crude in the cavity just above the water pump. I flushed a lot of it out with a hose BUT my concern/ question is :

Should that cavity drain or “hold” water ? In the picture it is the smaller , round hole in between the other openings. Mine does not drain and I think I may need to pull the water pump to see what’s plugged up. On the other hand ✋ I don’t want to if I Don’t need to.

Thanks for the advice.

Hi TOGNOT,
this is a blind area that allows hot coolant to heat the fuel tower and hence the fuel when the old recommended No3 Grade Furnace oil, later on with a change of classifications became No2 Furnace oil.
I guess to help break down any wax in cold weather.
From the SRB, for the D3400 Yellow engine book in the description of the Cooling System says of this elbow :-

" A portion of the warm water is transmitted through a connecting elbow to the forward side of the fuel filter housing to assist in warming the fuel."

Just saying is all :-
Be aware that these furnace fuels being less refined have a higher BTU content per given volume of fuel and so the engines produce Fu advertised Rated Power as compared to modern more refined Diesel fuels with less BTU per given volume.
When Dyno. testing engines at the Dealer we used to do Fuel Specific Gravity (SG) Tests and apply conversion factors from a Cat chart to adjust the HP output as per the factory test specific fuel SG of known constant value.

As part of the build process for the ANARE Antarctic Division Cat machines we used to Dyno test and adjust the rack settings to compensate for power loss due to using the less waxy highly refined Jet A1 or ATK so as the engines produced full advertised HP before these machines went for service down South.

Cheers,
Eddie B.

Cheers,
Eddie B.

Thank you for the reply. In the picture, the fuel tower is “upper right” . That’s not the passage I’m questioning. I’m curious about the round hole just in front of the cylinder head. Unless I misunderstand, that leads to the water pump. When i fill it with water, it does not drain down. I guess it could be a blind hole also ?

Thanks

Hi,
as Neil suggests, maybe your cooling system is drained to that level as water has to flow thru the round hole for the pump etc. to work.
Looking at the schematic it would appear that the round hole would be the by-pass passage for water flow around the engine when the thermostat is closed. I stand to be corrected.
Scan below from the the SRB for D3400 cooling system description and schematic.
Hope this helps.
Cheers,
Eddie B.

Thank you - the schematic is helpful. Yes, the coolant is drained . I can see in the schematic - just below the thermostat - water should flow INTO the water pump. Mine must be plugged with crud . I will try again to clear with wire etc, but probably the best plan is to remove the water pump and throughly clean all the barnacles from their home.

I can fill the center, round hole with water and it does not drain even with an open lower hose.

It seems #10 is plugged

Hi TOGNOT,
I agree and by the looks of the schematic there looks to be an reduction in opening size, to be an orifice, at the lower end of the return passage into the water pump so as limited bypass can occur--needs to be some restrictor there to force most coolant thru the radiator for cooling when the thermostat opens.
This new Scan may show it clearer.
Cheers,
Eddie B.

Thanks again. I will construct a more robust “orfice clearing tool” before i pull the pump off !