[77newell]

My dash heat has been lousy since I've had the coach. Forest reported that it was inadequate when he had it so this is a long term problem. I recently noticed that the heat is much hotter when sitting at a traffic signal and seems to diminish quickly when we start moving. I'm wondering if my boost pump and the engine pump are fighting each other. I have 4 shutoff valves, two for supply and two for return. I'm wondering if someone that has the 8V92 engine on a coach that heats really well going down the road would take a look at their coach and tell me the location of the valve that is connected to the inlet of the boost pump.

[folivier]

Jon if I remember 1 set of valves goes to the water heater and the other set goes to the dash heater and the heater under the bed (I added a set of valves to shut off the under bed heater).

[encantotom]

from what i have learned, everycoach was plumbed for the heater hoses with not a lot of consistency. my 90 was a maze of heater hoses.

and a booster pump above the passenger side headlights and another on the frame rail back by the engine. both turned on by a limit switch on the heat/cool lever on the dash that newell had added.

tom

[Fulltiming]

My 1992 has the valves on the engine and the booster pump as Tom described. Without the booster pump which comes on then the temperature lever is moved all the way to hot, the temperature isn't warm enough. There are also multiple fans. If one of them is out, you will have inadequate heat.

[encantotom]

On my 90 the booster pump came on at about 25 percent movement of the lever you could he hear the microswitch click

And there were 2 booster pumps

Tom

[77newell]

The booster pump and solenoid valve are operating fine My coach is set so both open when the heat lever is at about 50% or above. Below 50% there is no hot water flow at all to the front heater core. All the fans are working. I'm just wondering why, independent of vehicle speed, the temperature of the air coming out of the vents, with the lever full to the right for heat, rises when engine is at idle and lowers after a delay when the engine speed rises. I'm guessing, and just guessing, that the engine pump and the booster pump are fighting each other with the booster pump winning when the engine pump is at idle engine speed and the engine pump cancels out the booster pressure when the engine is revved. This could explain the pattern of symptoms I'm seeing and is why I asked for the location of the valve on the engine to which the inlet of the pump is connected. It would helpful to know where both ends of the dash heating circuit are attached to the engine but the return line will not be as obvious as the line connected to the booster pump inlet which is why I only asked for that one.

If it turns out the booster is implemented incorrectly it would not be a first for my coach. The backflow preventer on my hose bib in the water compartment was backwards so it prevented any water from flowing. The plumbing in our coaches is incredibly complicated and mistakes are not entirely unexpected.

[djimellis]

On my 87 the valve is located on the drivers side down in the right hand corner of the block. The other valve, I only have 2, is to the left & up, at the right end of the exhaust manifold. This valve controls the flow to my hot water tank. As for why your is warmer on idle then at speed I cannot think of what that might be. I removed my heater core, motors, vent tubes etc, to install a new floor in the compartment. It was not a difficult job but you have to have a bit of time on your hands. If you crawl under the front passenger side compartment you can see if the air intake ports are open or closed & you should be able to hear the pump working the therefore put your hand on the output hose to see if it is hot.  Good luck.

[77newell]

Jim, thanks for this very clear reply. Is the one lower right connected to a boost pump inlet or do you not have a boost pump?

I can feel the boost pump working and there is hot water flowing through it. I'm trying to figure out if the flow changes with engine speed.

My air intake ports make little to no difference in the temperature of the hot air output whether they are open or closed. What seems to matter the most is the inverse relationship of engine RPMs and heat out the vents.

[djimellis]

Jim, thanks for this very clear reply. Is the one lower right connected to a boost pump inlet or do you not have a boost pump?

I can feel the boost pump working and there is hot water flowing through it. I'm trying to figure out if the flow changes with engine speed.

My air intake ports make little to no difference in the temperature of the hot air output whether they are open or closed. What seems to matter the most is the inverse relationship of engine RPMs and heat out the vents.

Yes, the lower right shut off is connected to a boost pump. The boost pump does most of the water flow and if you have hot water coming out of the pump I believe your core would be your next concern, unless for some reason one of your 3 blower motors is failing. Have you tried reversing the electrical leads to the pump to see if that makes any difference? You won't hurt anything by trying that.

[Richard]

What happens if you disable pump? If they are fighting, temp should rise with rpm.

Or you could switch hoses at the engine and see what happens.