B7510 Thermostat Bypass (for Cab Heat)

NoJacketRequired · Nov 14, 2018

Am getting ready to plumb the cab heater to the engine. Some posts here have suggested using the thermostat bypass pickoff points. This would be especially handy for me since the specifics of this cab limit me to 3/8" (I.D.) hose.

Questions for the experts... - see photos below, the thermostat bypass hose is, I believe, the one to which I've attached some blue tape

1) if I attach the two heater hoses to the two existing hose nipples (one on thermostat housing, the other on the water pump housing) am I going to get a constant flow of hot coolant going to the heater?

2) which end of this thermostat bypass hose is considered the "pressure" side - the side closest to the pump or closest to the thermostat? I'm assuming I should treat the pump side as the "pressure" side and the thermostat side as the "return" side. Please correct me if this assumption is wrong.

2) the cab has a coolant flow control valve outside the heater core - this valve is sticky and I'm inclined to just leave it permanently in the "on" position. If I do happen to leave the flow control valve functional, should I tee into the hoses and install another valve (perhaps down by the engine) to essentially provide a "winter/summer" selection to ensure the thermostat bypass can continue to flow if I happen to turn off the cab heater valve during the summer?

Thanks for all your helpful guidance. This cab installation is coming along nicely. Once completed I'll start a thread to document the project. Too busy right now trying to actually get the work done to document it!

majorwager · Nov 14, 2018

My experience for all it is worth??

I purchased an aftermarket Agrital cab for my MX, they supplied stepped threaded hose barb male fittings for the thermostat housing on left and spare water pump port on right. Heater hoses are 3/8" from the port, then they furnished a 3 /8 x5/8 hose barbed increaser coupling.

The ceiling mounted, recessed heat exchanger has a shut off valve in the cab. This must be off in summer or I roast.

My tractor does NOT develop high operating temps in winter. This might be caused by operating RPM's in the 1200 range. The FEL is very smooth at that setting.

To raise engine temps, I place a sheet of. 019 alum in front of entire radiator screen. In addition I block the exterior fresh air intake filter w/ dense foam.

The ventilation system has interior cab ports (air intake) so inside air is just recirculated through the heater. This combo provides a constant flow of warm air to defrost and condition the cab interior.

In summer months, under heavy mowing load, and high RPM's the temp gauge will spike. Opening the cab heater core valve for a few minutes provides increased engine cooling, due to increased travel path of the coolant.

This does lower engine temp quickly as you suspected. Good luck.

Hope this info is helpful.

chim · Nov 15, 2018

I have a different model, but some can give you some info on mine that may help you think it through. After reading a scary post about skin grafts as a potential result of a hose rupture, I made all heater lines copper pipe within the cab.

NoJacketRequired said:
Am getting ready to plumb the cab heater to the engine. Some posts here have suggested using the thermostat bypass pickoff points. This would be especially handy for me since the specifics of this cab limit me to 3/8" (I.D.) hose.

Questions for the experts... - see photos below, the thermostat bypass hose is, I believe, the one to which I've attached some blue tape

1) if I attach the two heater hoses to the two existing hose nipples (one on thermostat housing, the other on the water pump housing) am I going to get a constant flow of hot coolant going to the heater?

That's how mine works. See also response to the second #2 question

2) which end of this thermostat bypass hose is considered the "pressure" side - the side closest to the pump or closest to the thermostat? I'm assuming I should treat the pump side as the "pressure" side and the thermostat side as the "return" side. Please correct me if this assumption is wrong.

When I connected mine, I didn't care which side was which.
The hot water goes through the coil in either direction. It's a simple coil and not a 3000CFM air handler

2) the cab has a coolant flow control valve outside the heater core - this valve is sticky and I'm inclined to just leave it permanently in the "on" position. If I do happen to leave the flow control valve functional, should I tee into the hoses and install another valve (perhaps down by the engine) to essentially provide a "winter/summer" selection to ensure the thermostat bypass can continue to flow if I happen to turn off the cab heater valve during the summer?

I have a bypass for the water that is open when the heater has no flow. On my install, the lines to the heater are 5/8" IIRC. There's a short 90 degree hose that was connected as a bypass from the factory.
One end was 1/2" and the other 5/8". I rotated that short hose and used a coupling for one heater hose. Then the second heater hose got connected to the spot where the short hose was removed. I'd be concerned about using a smaller bypass than was installed at the factory.

Thanks for all your helpful guidance. This cab installation is coming along nicely. Once completed I'll start a thread to document the project. Too busy right now trying to actually get the work done to document it!

mikester · Nov 15, 2018

You may have already have a port on the outlet side of the pump which will save you cutting an Teeing the lines.

Scroll down to the bottom of this posting for photos of the cab heater install.
http://divergentstuff.ca/index.php/2017/10/19/laurin-eclipse-cab-install-for-my-kubota-m59/

NoJacketRequired · Nov 15, 2018

Thanks for the great replies, folks!

mikester said:
You may have already have a port on the outlet side of the pump which will save you cutting an Teeing the lines.

I have what looks like a port on the thermostat housing, but in fact it is a depression in the casting rather than a threaded hole with a plug in it. I would have to bore out the hole and tap it in order to get a pipe thread-to-hose-barb fitting threaded into it. That's why the existing 3/8" hose barbs on both the pump and thermostat housing look like the ready-made solution.

BTW I mentioned in my original post that his cab requires 3/8" hose. That's because the cab has an overhead heater and the hoses run up the inside of the front cab structural pillars where 3/8" hose is all that will fit. My other B7510 has a Curtis cab and uses 5/8" hoses because it doesn't suffer from the same restriction in where the hoses run.

NoJacketRequired · Nov 15, 2018

chim said:
I have a different model, but some can give you some info on mine that may help you think it through. After reading a scary post about skin grafts as a potential result of a hose rupture, I made all heater lines copper pipe within the cab.

Thanks for your input. I've considered using copper but the passages up through the front pillars of the cab have some rough welds on the inside, welds that I fear would chafe the copper and eventually cause it to fail.

The bypass I would use would be the same 3/8" as that which is currently in place. Like you, I wouldn't want to try reducing the flow beyond that size and it would require the use of adapters when it's just so much easier to use 3/8" hose throughout.

NoJacketRequired · Dec 2, 2018

As a follow-up... I ran 3/8" hose from the thermostat bypass up to the cab heater in the roof of the cab and back to the water pump. As others who have blazed this path before me discovered, this solution makes LOTS of heat. So much heat that when I was doing a trial run, snowblowing right at the freezing point, I had to turn the heater circulation fan off as I was getting too warm in the cab.

Engine temperature indication was normal. And the cab gets heat very quickly.

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B7510 Thermostat Bypass (for Cab Heat)

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