Opinions needed regarding tapping my coolant system...

[gumpy]

Ok, here's the scenario...

I have an Aquahot installed which has a heat exchanger for preheating the engine and producing hot domestic water while driving.

I'm also installing a used webasto I picked up for not much $$$ as a redundant backup and for primary engine preheat.

I'm planning on routing the coolant from the engine, through the webasto, through the aquahot heat exchanger, and through a March mag drive pump and back to the engine, probably in that order.

MC9 with original over-the-road (OTR) heat still in place.

I'm returning the exchanger loop back into the 1 1/4"  OTR heater return line, just after the valve that's located on the floor of the a/c compressor compartment. Replacing the gate valve with a ball valve. Return loop of exchanger will be valved separately for full isolation of both loops.

My question is in regards to where I should take the supply from. Currently, the supply to the OTR heater comes from two taps off each side of the block, which join at the top of the engine, near the alternator, and run into the tunnel and forward. These look to be 3/4" galvanized pipe with an elbow, transitioning through rubber heater hose to copper. All good. Seems obvious and easy enough to take the elbow off the passenger side where the webasto will be located and the lines fromt he Aquahot come into the engine compartment, replace with a Tee and tap the supply in there. Simple and sweet.

However, farther up this line, there is a tap and line that sends coolant to the air compressor. This is between the block and where the two main lines come together before entering the tunnel.

My T would come before the air compressor coolant line tap.

My question is, how much coolant comes out the side of the block? Can I put a T on there, and redirect some of the coolant through a 3/4" line to my aquahot and not starve the air compressor of coolant?

The other option is to cut into the 1 1/4" line (after the two block taps coime together) before it enters the tunnel. This would be after the air compressor tap.

Clear as mud?

Anybody have an opinion here? Are photos required to explain this better?


craig

[Paso One]

I went thru what your going thru The issue I think that I had to deal with was too avoid cross flow when the engine was running. as when the engine is not running the webasto will draw from the lower part of the block and dump it into the top for example. Using the princple that the hot water will rise.  The issue I fought with was when the engine is running what direction is the water pump pushing the water where you are tapping the block.  I thought for example that tapping the plug on the front head the water was pushing out. Now when I tapped the back was it pushing out also.  Bottom line for me was I moved my return lines to the lower rad hose as FOR sure the water is being Sucked from the lower rad . I hope this answer helps  not make your decision worse. Paul

To answer your question yes I believe a lot of coolant will come out of the side of the block and in my opinion tapping it low will never starve your compressor.  Again the principle being that water finds it's own level.

[gumpy]

Paul,

The line I plumbed the return into is the main OTR heater return and goes directly into the lower radiator lines, so it will be sucking.

I'm going to use the pump to pull the water from the block, through the webasto, through the heat exchanger in the aqua hot, and back to the return line. The idea is that when running, the engine water pump will push hot water through the heat exchanger in the aquahot. When parked, I can preheat the engine by running the pump, which will suck water from the engine, and push it back through the return line.

The other thing I'm  concerned about is that when preheating the engine, the water will have to circulate THROUGH the engine water pump. Not sure how much resistance there will be there.

[kyle4501]

The other thing I'm concerned about is that when preheating the engine, the water will have to circulate THROUGH the engine water pump. Not sure how much resistance there will be there.

I'd think that the engine's water pump has enough clearance in it to allow sufficient bypass. You are preheating the engine, not cooling off 300HP climbing a mountain, so I wouldn't think you needed tons of flow.

I haven't done any calculations, so this opinion is only worth what you paid for it. 

Maybe someone has some fancy gauges you can use to plot the pressure at each point in the system & know where the restrictions are & if you are in danger of aerating (?) the coolant which, by now, everyone should know is surely the cause of all cooling system problems in any coach . 

[Burgermeister]

Kyle, 

That "fancy guage" your speaking of is a coolant system manometer, an example of which I plan to bring with me to Busn'2007 and Bus'nUSA 2007.

For Webasto, block heating purposes, the coolant pump is a (mass) slinger and, as you stated, shouldn't provide appreciable resistance.  The capillary effect resistance through the radiator would appear to provide greater resistance than the coolant pump (just a guess!).

Marc Bourget

[gumpy]

Yeah, I guess the secondary issue of pushing through the DD water pump when preheating the engine was of lesser concern. I really don't think it will be a problem, but have heard (or read) that they can cause some resistance (or maybe I'm thinking of the fuel pump when adding the electric primer).

Right now, my biggest concern is whether taking a 3/4" line off the block tap will starve the air compressor cooling system or not. I'd hate to burn that up for the sake of generating a little domestic hot water.

[kyle4501]

If I were to do this , I'd tap in at a convient reasonable place & try it. If you add a temp gauge to the outlet of the air compressor & see what is 'normal' before the domestic hot water heater loop is added. Then it will be easy to know if you're starving the compressor for coolant.

Another idea (may be dumb ) What about adding a tee fitting to take the coolant from the compressor feed line to the domestic heater & returning it back to the compressor? (use a check valve to prevent short circuting)

Just a thought...

[gumpy]

Interesting ideas.

Might be able to do the air temp one. I'll have isolation valves on the loop, so I could run it both with and without the loop and see what the temp differential is.

The Tee idea probably won't work. I'm concerned that my loop is already too small for the extra webasto (it's a 80K BTU unit, but I'm going to nozzle it down to 45K btu). I'm afraid the check valve would add more restriction to the loop. The heat exchanger in the aquahot is already only 1/2" copper, so I'm squeezing it pretty small already.
I may put some valves in to isolate just the webasto and pump to be used for engine preheating, or possibly put to put the aquahot in parallel with the loop. Still thinking about his part of the loop.

[Paso One]

I put a T in the line where my 1500 watt electric circulation heater gets it's feed from.  I too have a loop that heats domestic water while driving down the road. The line also feeds the webasto 45,000 btu unit. According to webasto service dept the webasto is designed to allow water to circulate past it's pump when not in use. I robbed a circulation pump from a old Fishbowl and put it in the same loop. I can trip a toggle and it pumps to beat the band. I don't know the long term results of this but it sure moves the water.
I put it in the loop because I felt the loop didn't have the circulation it should. ( I determined this by a scientific calculation )   putting my hand on the hose It wasn't as hot as the same hose closer to the motor   Paul

[Nick Badame Refrig/ACC]

Craig,

Check out this pdf from my Proheat. It has diagrams of how to hook into the cooling systems of many different

engines, including detroits.

http://www.proheat.com/PDF/XL900_1500_Service.PDF

Nick-