Does it matter which way heater hoses are hooked to heater?

Nickathome · Post by **Nickathome** » Wed Jan 21, 2009 5:30 am

This may seem like a dumb question, but does it matter which way I hook the hoses to my M151 heater? I understand the coolant flows into engine from the bottom hose, so I figure the flow would be from the bottom hose, through heater then back through block hose? Does it really matter?

DaveO · Post by **DaveO** » Wed Jan 21, 2009 6:14 am

That's the way I did mine, but I don't think it really matters.

knattrass · Post by **knattrass** » Wed Jan 21, 2009 10:37 am

Nick - on the M37, there is a plug right on top of the block at the rear by plug #6 on the passenger side (see the shutoff aimed forward). The head core is stamped "heater" around it. Tap into that, run to the heater, from the heater, run to the top of the water pump where there should be another plug or use the one in the discharge pipe. The M37 heater kit that I got installed a shutoff at each plug in case you have a leak you can isolate the heater as well as shut the heat off in the summer.

knattrass · Post by **knattrass** » Wed Jan 21, 2009 10:39 am

Oh, the orientation does matter because you want the hot fluid from the back of the engine to run thru the heater not the cooler fluid from the front.

Nickathome · Post by **Nickathome** » Wed Jan 21, 2009 11:23 am

Knattrass;

I have the hookup points, i just thought there was a coolant flow to be maintained.

knattrass · Post by **knattrass** » Wed Jan 21, 2009 11:41 am

Yikes - I just re-read your original and obviously you are looking at the 2 pipes on the heater not the engine... ok its cold here and numbs my mind. Unless the tubes are marked with arrows, the small coil wouldn't know if the fluid was flowing north-south or south-north. I know on my Red Dot heater they are marked and it does matter.

Post by **Cal_Gary** » Wed Jan 21, 2009 1:00 pm

My Mutt heater has the flow direction marked-I followed the flow pattern on install and the hotter coolant flows from the back of the head into the upper heater core then exits through the bottom of the core and out to the water pump fitting. I wouldn't think there would be much noticeable difference in temps whichever way the hoses are routed, unless one is in the Arctic. Hey, it's heat (not that I needed it last week with 70 degree temps outside-nice)!
Gary

Nickathome · Post by **Nickathome** » Fri Jan 23, 2009 3:22 am

I checked on my mutt heater and I did not see aa flow direction marked on it. Looking at photos I was given of other's heater installs, they all seem to have the hose running from the head, to the upper most pipe on the heater, and I will hook mine up that way.

I see also that some have the one hose hooked to the plug on top of the water pump, while others have it hooked to the plug on the lower radiator hose. I bought valves to fit the plugs on the head and lower radiator pipe as they are the same size (3/8ths pipe thread). The plug at the water pipe is half inch pipe thread and thus a larger valve would be required. I was more concerned about the flow through the heater core itself than anything. Thanks for the replies.

HingsingM37 · Post by **HingsingM37** » Fri Jan 23, 2009 3:47 am

Nick,
Your post promted me to investigate my heater. I looked at my pre-disassembly pics and the hose from the cylinder head ran into the top inlet of the heater core and the outlet went to the valve in my lower radiator tube. My heater is a small 14x14 unit made by a company in Cleveland, Oh but it is not a not Hunter MFG. military unit.. It appears it was some type of generic cab heater perhaps for construction equipment. I tested the blower motor the other night and was glad to see it worked. Of course I got nailed in the face by acorn nut shrapnel probably from some squirrel or chipmunk using it for a home these past few years

Post by **Cal_Gary** » Fri Jan 23, 2009 6:47 am

Nick, yours is routed like mine; however, my metal lower radiator hose didn't come with the pipe bung, so my return tube flows into the top of the water pump by-pass-works just fine.
Gary

Nickathome · Post by **Nickathome** » Fri Jan 23, 2009 7:13 am

By all that I've read thus far, it seems as long as there is some sort of flow, then all will be well. The jist of the matter though is that most agree that the line from the head goes into the top pipe of the heater core. Works for me.

Lifer · Post by **Lifer** » Sun Jan 25, 2009 5:35 am

Look at it logically! The heater is basically one big pipe that separates into a whole bunch of little pipes and then goes into another big pipe. That's all there is to it. The pipes don't give a rat's butt which way the water flows...up, down, or sideways! The water will flow from the block, through the heater core, and back to the water pump no matter which way you plumb it. If your heater has one of the big pipes labeled "input" or "in," the hose from the block should go there, but the heater core won't really know the difference unless it has some kind of baffle system built into it.

Does it matter which way heater hoses are hooked to heater?

Does it matter which way heater hoses are hooked to heater?

heater flow.......

Direction...

Flow