Heater/Defroster Circulation Pump

[Oonrahnjay]

    I've added a couple of extra heat exchanger/ fan module heaters to my bus system.  It was originally built with a single loop for the defroster running along the center of the frame from the engine to the dashboard.  Since I've added the extra heaters, the amount of heat from the defroster (which also supplies driver's heat) has dropped significantly.  The whole loop is a great big ole mama bear to bleed air out of but I think I have it reasonably well bled.  But I'm wondering if I should have a circulation pump on the loop to move more hot water through it.

    I have both 12V and 24V power supplies available but I think I'd like to power such a pump with 12V.

    Has anyone run into similar issues?  Did you install a pump?  How much current does your pump draw (and what voltage)?  I'd appreciate any discussion on this.

Thanks,  Bruce H   NC  USA

[artvonne]

  All the Buses we scrapped had circulation pumps, GM, Flxible, AM General. GM's ran something like 1 inch ID copper lines forward and the pumps flowed a lot of coolant. IIRC the lines were choked down to 1/2 inch north of the heat runs going to the cab heater (been 25 years I kinda forget).

  I found it interesting my MC5 has no pump (at least I have yet to find one) and only 1/2 inch copper line running forward to the cab heater. Main heater core looks to have much larger lines, likely 1 1/2 from what I can see.

  I guess my point is that a pump isnt going to harm anything and will provide greater flow. The Bounder didnt have a pump and I got very little heat out of it. I never installed a pump but considered it. Perhaps they built these Buses for a particular region? A southern Bus wouldn't need anywhere near the heat output of a northern Bus. 

[Geoff]

Check this one out:

http://www.ebay.com/itm/320857282930?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

--Geoff

[bevans6]

Paul, your MCI takes pressurized coolant from the back of each head, takes it to a tee piece behind the engine and sends it towards the main heater core, the return is to the lower passenger side rear where you can see the demand valve, thence to the bottom of the water pump along with the return from the passenger side radiator.  The drivers heater takes pressurized water from same tee behind the engine, sends it up the drivers side vent housing (with a close off valve up beside the rear of the alternator) up to the drivers heat valve and to the drivers heat core in the dash.  The return comes back and feeds into the return feed from the driver's side radiator to the bottom of the water pump.  

It's remarkably easy to trace this stuff when you have removed the engine and are sitting in the engine bay for several house, scraping off 30 years of solidified grease and bored out of your gourd...  the mind wanders to "I wonder where the drivers heat piping goes?"  There is no external pump, it all works of the engine water pump.  Unless someone changed it...   

Brian

[luvrbus]

You really don't need the high power pump from a OEM the little Marsh magnetic pumps works well and draw very few amps

[artvonne]

There is no external pump, it all works of the engine water pump.  Unless someone changed it...   

Brian

  I didnt think so. I traced it all pretty well, but havnt seen back behind the alternator area or cab electrical panel enough so wasnt sure. Last I had it running was to add some antifreeze, but didnt really run it long enough to get to operating temp. Still, I saw 160 on the gauge and upper T stat housings were hot, but not a lot of heat at the cab or main heater.

  I was surprised the copper lines to the cab are just attached to the metal wall and are uninsulated. I noted a temp drop between the back where they came off the engine, and up front just before they go behind the electrical panel. That will be remedied. I also dont think a pump would hurt anything. Could even plumb in a bypass.

  But seeing as you live in the sunny north, you likely have better knowledge of its heating ability, does yours still have the main and cab heater?? Hows it work??

[Cary and Don]

There is a shut off valve at the engine on the coolant line going forward to the front defrost.  This valve was half way open when we got the bus.  Is there any reason why it shouldn't be fully open?

Don and Cary
1973 05 Eagle
GM 4107
Neoplan AN340

[bevans6]

Paul, the drivers heat works well to defrost the windshield and keep it fog-free.  It has some ability to heat the drivers area but when you look at it you see there isn't a ton a airflow directed there - mostly to the windshield.  You should either keep it or figure another way to keep the windshield clear of fog (which can happen at quite warm temps).  The OTR heat works great - my temp control doesn't work so I moderated it with the turn valve on the return line, and just toggled the fan switch on and off, and we were quite comfortable on a below freezing drive.  I don't like to run the bus in snow and salt, so I haven't driven it when it's been really cold.  There is a bleed valve on the drivers heater core behind the dash panels.  I wouldn't add an external pump to a system that works perfectly well unless I was really bored and had a bunch of money that I desperately wanted to get rid of and had absolutely no other use for...   

Brian

[luvrbus]

Booster pumps are common on a 40ft + bus not so common on the 30 to 35 buses

good luck

[TomC]

The 12v booster pump I have in my AMGeneral flows water through when it is off, and boosts when kicked on for more heat.  When just using the front defroster, it isn't needed. I kick it on when the big heater is needed (the original heater core).  Good Luck, TomC