Geoff Weeks

The bypass line is use until the T stat is full open to return the coolant back to the pump to allow it to circulate within the block. The bleed line or passage prevent any air from being trapped in the future. Injector copper sleeves can weep a small amount of air into the coolant on start up. the bleed line or passage makes sure it doesn't get trapped in the top of the pump housing. Run a de-aeration tank low, and you can get air into the system. By allowing it to escape, you prevent the pump from being air bound. Take a picture of which lines you are talking about and I will try and tell you the reason for them. In all cases, the outlet of the water pump is directed to the bottom of the block, this makes the outlet of the pump lower than the top of the waterpump housing. That makes the housing an air trap. There are some (tend to be lighter duty engines) where the outlet of the water pump is to the top of the block or cylinder head, these self vent but direct the coldest water to the hottest part on the engine, which isn't great for even cooling. Most modern engines direct the outlet to the bottom of the block.

There are two reasons, for a pipe from the thermostat housing to the pump. One, is a return when the 'stat is closed (bypass), this keeps the coolant circulating. This, however tends to be a larger pipe, and is connected to the inlet side of the pump. Often a small hose or pipe from the pressure side is exactly what I am referring to, a bleeder line to to high point in the block to allow the air to escape. In Larry' s engine the bypass connects back down at the oil-cooler so not directly connected to the waterpump. depending on how the waterpump is situated on the block, the bleeder can be internal or external with a line, in each the reason is the same to eliminate a pocket of air. For the last aprox 50 years, a bottom fill/degassing tank has been used to eliminate air in the cooling system, with vents lines in the upper water rail and in the upper radiator tank. On a 3406 the pumps is low and gear driven, there is a large passage from the T stat housing back down to the pump ~1.5" diameter, when coolant from the degassing tank (where the cap and fill are) is directed to the inlet of the waterpump and the air can escape up the bypass line to the T stat housing (and upper water rail vent line) to the degassing tank. Since the bypass line is vertical from the top of the pump, the air pocket is eliminated. Cummins does it different with the waterpump bolted in a casting on the front of the block, with a small hole through to the main coolant passages in the block to allow air to vent out of the pump recess in the block into the main coolant passages in the block and on to the upper water rail.

No need for "bleeders" all over the block, because there aren't cavities that can trap air all over the block. Block has opening on top to the heads, heads have opening on top to the upper water rail, upper water rail has a vent to the degassing tank on top of the radiator. Yes, we could agree but then we both be wrong, as you say.

really no comparison, when you are looking at older mechanical engines and trying to compare to newer electronic ones. The L-10 topped out at 300 hp mechanical, but was more common at 240hp or 2 hp over an old 6-71! Gear ratio/tire size also makes a big difference. The whole truck has to be spec'd for the job to make the most of any one component.

Worked on Deere engines in river tow boats.

3406 is over 14L, L-10 is 10 liter, not a fair comparison. L-10 was kinda gutless but it was small and topped out at 300hp in mechanical form and 330 in electronic at the end of its life. It was replaced by the M-11 a "stroked" version, that was electronic from the get-go and that got power up over 400 hp. I had the experience of driving both an L-10 and a 3306 which were a closer comparison, in the same service with the same loads, and I felt the L-10 was slightly better than the 3306, both were 300 hp and the Cat blew the timing gears early in its life, the L10 lasted a lot longer. IIRC I got in the mid 6's for fuel with the L-10, about what my 6.9 did in my service truck! Both Cat and Cummins were pushing these small displacement, mechanical engines as fuel savers, over their large bore engines.

It has nothing to do with pressure, it has to do with an inverted U bend (at the top of the housing) that is above the inlet and outlet. It forms a pocket that holds air. You can have gravity or pressure on the coolant and it still will not cause the air to go below the coolant level to pass out of the pump. If you force the coolant in under pressure, you will compress the air trapped but not eliminate it. A vent line from the top of the housing allows the coolant to push the air out of the housing, gravity is more than enough to do this if there is an outlet at the top. If the outlet to the block was at the high point of the pump housing it would not be needed, but that isn't how this pump is made. By getting the air out of the housing, it makes the pump move coolant more efficiently, and leaves no air bubbles in the coolant to break on contact with the hot block and cause cavitation damage. All engines have some way to vent any air out of "high spots" in the system. Some have a small hole in the thermostat or a place where the stat doesn't seal off so air can pass. Others with Weir-stats, have a vent line to the degassing tank on top of the radiator. Air will not dissolve in coolant, it will always try to be above the coolant, if you provide a trapped area with no outlet with coolant below, it will occupy that space. Having an air bubble trapped in the top of the pump housing is like running a boat propeller 1/2 out of the water!

Yes, that will bleed it. You will notice in the diagram, the coolant "conditioner" is above the pump housing and runs to the thermostat housing.

How did they vent with the new housing? problem with bleeding once, is if the block ever gets drained, you have to do it over. IDK Macks but others sometimes have a internal bleed hole to vent the top of the pump housing.

That is not what I am saying! The inlet to the pump is at 3 O clock, the outlet is at 9 O clock (really closer to 4 and 7 oclock) , and there is no way to get the air out of the top of the water pump housing. Air will be trapped in the housing with no way out. It will cause cavitation. With that 3/4" nipple at the high point air will be pushed out of the waterpump housing. If you plug it there is no way for the air to escape. You'll end up with an air bubble. A bleed line out of the high point will force any air out of the pump housing and eventually to the top tank of the radiator.

Keep in mind you want some way to vent any trapped air at the top of the w/p housing. It doesn't have to be large (3/4") but some way to get the trapped air out. -3 PTFE line would be plenty. If it were mine, I'd cut the tube off and tap for a fitting to reduce to 1/8 NPT and a small breather line to the high point in the cooling system.

As far as Power steering, it depends, on what gear you have. Sheppard takes 10-40 motor oil as per Sheppard. 15w-40 has been the oil of choice until recent engines. Trans depends on what transmission. Look to the manuals, for the last word.

This shows the lower rad connection, through the oil cooler to the center of the waterpump. Yes, you need to vent the scroll to prevent air being trapped, but centrifugal pumps ALWAYS pump from center to outside. Where the outside is connected to the block (top, bottom or side) doesn't change the fact that it is on the pressure side of the pump.

This was the one.

I think you have that backwards, it draws through the oil cooler to the center of the pump, centrifugal pumps always pump from center to outside. The block is on the pressure side of the system. edit: hum the post I was replying to seams to have been deleted?

One looks to be on the pressure side of the pump (new one on top) while the other is on the suction side (lower). Not interchangeable.

There does seam to be something about the last name "Green" no matter how it is spelled, disrupting the SOU speech. I agree with 67Rmodel, it isn't just one side.

Any updates?

I hope I still have another good 10 years in me. I went looking for an older animal to take care of, Puppies often get adopted 1st (but don't always get to stay in that home😒). 5 years old was on the younger side.

Spoke hubs are all inboard drums, they have to be!

Koda, joined our family in Jan at almost 5 years old. Lost my last one in November, and I need some time to grieve before opening my heart to another.

I don't know much about the actual conversion, what was re-used and what was new. The engines were Detroit 11.1 L 60 series, and the transmission I think were Meritor. I remember the ads, "new truck for the price of used". I don't know if the frames were the same, it would look that way, otherwise why were the wheelbase limited to short conventionals? It was doomed from the start, the 11.1liter Detroit was the 1st electronic engine and while not bad, the displacement and power were not what people were looking for. I can't remember if the 12.7 L was a option or not. They were trying to use up what was already in the chassies. The bodies looked like Freightliners "business class" mid range with a hood that was different then their other trucks IIRC. That would seam to indicate that the original cabover frame was used and parts from newer trucks would't work. I don't think the program was a success, by any measure. I didn't pay much attention, as I wasn't in the market for new trucks, I always bought used and held onto what I had. When I retired, I sold my 1st truck I ever owned, it remained with me for the whole time. It was used when I bought it.

Paul, for a while Freightliner was converting their old leased cabover "turn ins" to short wheelbase conventional sold cheap. I don't know what all had to be changed, but they had leased so many cabover units to the big carriers that got turned back in when the length limits went away. No one would buy the old units, and they had to either export, scrap or find some way to get some money out of them. They overhauled the engines and transmissions and offered a warranty close to that of their new trucks. Still, there were not many "takers", some farmers that needed something cheap to haul short distances, bought them. They didn't learn their lesson, and there were a ton of conventional turn-ins a few years later. Used to be a huge storage yard not far from me of Freightliners sitting in a field, They would try and sell through dealers, but most just sat.

Ahh, the beautiful Iowa scenery!

Beautiful work. Labor of love not expedience. For a trailer, I would go another route. I got what was left of a parts truck. It had been cut up to make a dump trailer out of a rare tandem drive K series IHC. The complete truck, un cut was worth far more than putting the dump bed on some frame rails and a suspension.