J13 Water pump heater hose inlet size?

[XXL]

I'm not able to get to the truck at the moment to unscrew and measure.  I was hoping somebody might have a spare laying around they could measure for me.  I'm looking for the thread size of the female threads on the top left (driver's side) of the water pump on the J13.  This is the threaded hole that has a nipple fitting on the other end, that attaches the radiator hose running back to the heater core.  And... is the rubber hose 5/8" ID?

 

 

 

 

[MikeRL411]

Yes, as close as you can come to SAE sizes 5/8 is the size.  Ask me, I have a reel of 1/2 inch original Datsun heater hose doing me no good.  Now the bad news,  Replacement water pumps assume that you have the original pump and can swap the heater hose fitting.  I have no idea what size it is.

[zed1]

MikeRL411,

Is the hose you have the cloth covered rubber?

Keith

[XXL]

Thanks for the quick replies.  Hose on there now is generic rubber, and visually looks like 5/8" (the 2 most common sizes 'on the roll' at auto parts stores is 5/8" and 3/4"... this is definitely not 3/4").  Water pump was replaced by PO.  I'm not trying to replace the pump.  I'm looking to make a mod to the hose... and need to pick up appropriate fittings.

[XXL]

 Ask me, I have a reel of 1/2 inch original Datsun heater hose doing me no good. 

 

So the OEM heater hose was 1/2" ID?  Is that the size (OD) of the heater core inlet tube?  If yes, I guess the PO may have shimmed it a bit so the 5/8" hose could be clamped tight (???).  If 1/2" ID hose is what came on the truck originally, that will actually make what I'm doing much easier.  Please confirm.

[XXL]

So the OEM heater hose was 1/2" ID?  Is that the size (OD) of the heater core inlet tube?  If yes, I guess the PO may have shimmed it a bit so the 5/8" hose could be clamped tight (???).  If 1/2" ID hose is what came on the truck originally, that will actually make what I'm doing much easier.  Please confirm.

 

Anyone?

[Conner]

I don't know for certain for the J13 but I can tell you the E1 series engine from a 1965 L320 truck water pump used a 3/8" Male NPT fitting with a 1/2" hose barb.  And that's because it used 1/2" I.D. water hose.  The E1 and J13 are very similar engines.  The fitting I got for my water pump was Moroso 65390.  HTH. 

[Conner]

What water pump are you using.  I used a Gates 42324, which crosses over from the 320 (E1 engine) and the 66-68 520 truck and the 1969 521.  I believe that is the J13 engine. 

[XXL]

I don't know for certain for the J13 but I can tell you the E1 series engine from a 1965 L320 truck water pump used a 3/8" Male NPT fitting with a 1/2" hose barb.  

 

I just received the fittings I ordered the other day... and, of course, I got the wrong one.  I had measured the raw thread size of the NPT fitting with a micrometer, but evidently didn't get an accurate read.  So, I ordered 1/2" NPT.  It's too big.  So, a few minutes ago, I pulled the hoses loose so I could make sure and get a good read, and... as you indicate here, it looks like it's 3/8" NPT (about 0.65" on the threads).  So... ordering AGAIN.  Once I get the parts I need, I'll post some pics of the mod I'm doing.

[Conner]

Also to be 100% certain on the hose size (1/2" vs 5/8" ID) you can put a caliper on the outlet from your heater core that should be sticking through a hole in the firewall into the engine bay. 

[XXL]

Also to be 100% certain on the hose size (1/2" vs 5/8" ID) you can put a caliper on the outlet from your heater core that should be sticking through a hole in the firewall into the engine bay. 

 

Yes, I have since confirmed it's 1/2" ID hose.  I had not been in a position to actually take it apart enough to get a good measure until today.  Because the hose was pushed up so far on the barbs (both the water pump and heater core ends), I couldn't get a good reading with my caliper or micrometer.  Today, when my (wrong size) parts arrived, I was able to take the hose off and measure properly.  Had I done that BEFORE ordering the parts, I could have saved myself a small headache... oops.