Joined: Aug 31, 2010 Posts: 1740 Location: SO IDAHO
Posted: Thu Jan 15, 2015 8:40 am Post subject: water pump question from 4X4M38
Hi Rick,
On my M38 I have a two pulley water pump on my rebuilt engine. It has a rebuild tag on the block so I'm pretty sure it's military.
The water pump has a small (1"?) hose running from the top right of the pump housing over to the right side of the engine and it is attached to the motor where the M38 temperature sender goes. There is a splice and a fitting, and an electric sender in the fitting.
Is that a Civvy thing? I don't see anything in the M38 literature about that extra line fr0m the water pump, but some photos show a plug in the pump casting.
Thanks,
Brian
_________________
Brian
1950 M38
MC11481
*********************************************************
This question was PM'd to me and I don't have an answer other than its not stock. Best to share it with the board and get more informed opinions..
Brian should have the bypass hose from the WP to head as shown here but apparently has another hose from the WP plug shown in lower left of foto to the temp sender port with some sort of in-line sender installed. Sounds like the PO didn't have a stock sender and improvised.. _________________ keep 'em rollin'
RICKG MC 51986 DOD 01-52, '50 CJ3a
Joined: May 14, 2009 Posts: 971 Location: South Dakota
Posted: Fri Jan 16, 2015 6:20 am Post subject:
I have a CJ with the "T" ( more like a "y") arrangement at the temp sender hole. If the head isn't drilled at the rear top, then it draws water at the sender hole for the heater. If the head isn't drilled at the front for the bypass M38 hose,then I guess they ran it back to the temp. sender. Never seen that done before. Most likely a owner's modification. The plastic oil pressure sender line is a civilian thing also. If his engine's head has the cast flat on the front, he can drill and tap it for a bypass and eliminate the hose from the pump to the temperature sender hole and install the small 90 degree correct hose. Wonder if his head has the hole at the rear top? The civilian L heads didn't have the front bypass hose and needed the small bypass hole drilled or provided in the thermostat.
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Fri Jan 16, 2015 10:31 am Post subject:
Hi Guys,
Thanks for the replies.
I have a remanufactured engine from Pueblo, Co., 7/55. It has an M38 head as well. I took a look this mornign and there is a pipe plug in the head at the boss pointing towards the radiator. The hose in question runs from the water pump connection to the right, then back on the right side to the connection for the temp sensor.
So end of the day, the provisions are there to remove the pipe plug and screw in the proper fitting and bypass hose. I guess in the meantime it's ok to run as is?
Be sure to understand the purpose of the original M38 set-up. It was a water pump bypass feature that was added to improve rate of warm up. Preheated water would leave the head and mix with cold water from the radiator speeding up the warmup. M38's did not come with heaters.
On civilian jeeps with heaters the same purpose is accomplished through the heater plumbing. The water pump draws cold water from the radiator and pushes it through the block and the heater plumbing the most of the return heated water goes straight to the radiator but the heated water that went through the heater and head is returned directly to the water to help with a more rapid warmup.
The correct way to plumb in a heater is hot water to the heater from the side of the head and then route heater return to the port in the top of the pump. If the head has a front port it then is plugged. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Fri Jan 16, 2015 2:54 pm Post subject:
Hello Wes,
This thing does not have a heater, military or aftermarket.
After reading the above posts I have no idea why that line was
plumbed that way and the front head port plugged.
I was thinking about a jacket water heater, not a passenger compartment heater, but obviously this is neither. A photo is worth a thousand words!
Bubba strikes atgain! _________________ Chuck W.
Dixie Division MVC #002
1952 M38/M100
M274A2
1964 CJ3B
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