MCI 102C stock webasto info

[buswarrior]

I think we are stumbling onto a problem for those busnuts who start abandoning parts of the coach HVAC.

Running with the HVAC shut off, where's the coolant going?

Happy coaching!
Buswarrior

[Paso One]

ON THIS UNIT. When both valves are closed the water circulates thru motor then webasto and the two "y's"  back to the motor.  I just looked again and water has to circulate thru the Auxiliary heater ( webasto ) the only shut off in this stock system are the two that sends the water to the HVAC .

Certain combinations ie: webasto solenoid open But highly improbable valve to front Closed the water would still go thru Y back to motor.
Looking at this Cat set up it's " idiot proof " 

[Paso One]

This "bypass valve" that allows coolant to shortcut back to the cold side causes me concern. How does it work, and what is its failure mode? That's an overheated engine looking for a place to happen?


Happy coaching!
Buswarrior

Sorry Ewen forgot to GMHO on this bypass valve. If stuck open water free flowing if stuck closed it would back up the water and force it thru the Y back to the return side,

Jim your 1 to 6 list looks like the words to "old Macdonald had a farm " 

[Jim Blackwood]

OK, as I see it, If you close either of the two valves to the heater loop all you have left is the flow through the webasto, to the solenoid valve, and then to the return. If the solenoid valve is closed, how is there going to be any coolant flow? I don't think there can be. Double check the drawing. So, at that point coolant flow is through the engine, the radiator and the transmission heat exchanger only. I THINK it has to be from the engine and heat exchanger then to the radiator but I'll have to look again. The return from the heat exchanger may go back to the water pump.

Anyway, the solenoid is the only HVAC flow control that I have been able to find, and I think it is the only one in the schematics as well. So the only possible way that it could work for that function is to short circuit the flow through the heater loop, thereby reducing  but not entirely shutting off heat to the HVAC. What this means is that when heat is not required (think summer in Nevada for instance) the flow through that 1" line is directly bypassing the radiator. This strikes me as a singularly inefficient way to do things. But that doesn't make it incorrect.

Unless of course the manual valves are closed and the solenoid valve is closed. In that case, no bypass and no flow in the heater loop. Opening the solenoid would then reduce the heat sent to the radiator, keeping more in the engine and transmission.

The system seems designed not so much to get rid of heat as to provide multiple way to retain it. Do 4 stroke diesels really run that cool?

Jim

[buswarrior]

The earlier buses, the coolant only flows to the hvac heat exchanger as the control valve allowed, so there were periods of time that the flow through the hvac lines was stopped.

The temp control valve will be in close proximity to the hvac equipment, not in the engine room.

What powers this bypass solenoid valve?

I drove DL's back then, and they were quite capable of overheating, also capable of cooking automatic transmissions...

Everything is a contradiction, retaining or making heat is desirable sometimes, the very same stuff leads to overheating in other conditions...

This bypass valve is becoming suspect #1 for trouble later on...

My friend has the webasto lines tied together for the moment, due to leaking bits on the webasto. Spare parts are months and couple thousand miles away, he isn't going home til spring.

But the coach is overheating...

Never a dull moment for a busnut?

What powers that bypass solenoid? If a wire has been left off/broken...? Any reports of these failing open?

Happy coaching!
Buswarrior

[Paso One]

Dam i hate when you lose everything in a post if you over load it ( assumption. ) pictures and text gone,  so much for long posts.

Anyway the bypass valve according to the manual is a Normally open valve.
Attached again are the pictures before and after the valvw.

The valve has both electrical and air connections, There is an identical valve in the HVAC compartment.
I'll add a second post for fear of losing it again.

[Paso One]

This is the other side of valve upper picture is the other side.
I wonder where the bus nut bypassed the webasto??

[Paso One]

Missed the other side of the valve picture.
If it is overheating since the bypass where did he bypass it has got to be the # 1 question.

I hope I am helping here.  as i really can't see it since both valves can routinely be closed. ( gate valves)

[Paso One]

Okay not willing to let it go I went back to the engine and looked for the " Lazy Mans " way of bypassing the Webasto. ( no offense intended as i am guilty of the lazy mans way lots )  Low and behold if he took the inlet and outlet hoses off the water pump ( they are not close but real handy )  He could indeed reduce engine cooling as the water is going in and out of the pump not pulling  coolant from the engine.
Hope that makes sense...... remember i'm on a Cat engine. water pump is back left of engine.

[Jim Blackwood]

So far all posts except that last one are consistent with what I'm seeing here and I'm just not sure what the last post means, it may be as well. Now that you mention it I remember the solenoid valve up by the main heater core. Both it and the bypass valve are described as being the same part but inverted in the controls. Therefore when the heater valve opens the bypass valve closes. That is consistent with good operation for heat, but seems it would reduce engine cooling in hot weather. Under those conditions it would seem to make sense to close the bypass valve as well.

I had disregarded the heater control valve because it does nothing to further my goal of isolating the engine from the webasto/HVAC loop.

re: the immediate issue, bypassing the webasto due to leaks should work, if the rest of the system is functioning properly. If it is overheating it would seem prudent to close that bypass valve by whatever means available. As it is described as normally open (I believe) it would be necessary to make sure it closes. So, verify air and signal and confirm operation.

Jim

[buswarrior]

Thank you gents.

The control logic for this bypass valve sounds good, under conditons of cold engine/cold coach.

It makes no sence to feed hot coolant back into the water pump intake under warm conditions...

There must be a temperature component to the control of this bypass valve, or tied into the Webasto firing circuit, to keep it closed when the engine temp is satisfied?

Happy coaching!
Buswarrior

[luvrbus]

Webasto and Pro Heat both are plumbed the same,the bus probably has a L10 or M11 here some photos for the Cummins,there are isolator valves (3) not showed but it will give you the idea on how they plumbed  on the engine if that helps