Ford lehman 120 #6 cylinder

BruceK said:

If I remember the Manual correctly, opening the petcock was advised when topping up coolant. Rarely if ever did air bleed instead of coolant. If you are getting air accumulation daily when cruising something seems amiss.

Click to expand...

It's been doing this for 20 years. I pressure test the engine every spring and no leaks. Coolant rarely needs topping up.

Bob Smith thought it may be caused by cavitation but I don't see how that could occur in the pump. He also though, during a different conversation, that air was mixing with the coolant in the expansion tank from the turbulence.

Since the engine maintains correct temperature under way and does'nt lose coolant, it's more of a mystery than an issue.

Soo-Valley said:

It is said not to open when engine is running as it will suck in air. If you did plumb to expansion tank bottom it would suck fluid, that would bypass the thermostat?

Click to expand...

The manifold is under pressure while the engine is running so opening the petcock would actually cause coolant to shoot out. Maybe it sucks in air after coolant system pressure is relieved.

Yes, the coolant would bypass the thermostat but only the volume that can pass through 1/4" tubing. I'm not sure if it's enough to interfere with normal thermostat operation since the other coolant hoses are 1 1/2" or larger.

I recently modified the hose routing on my Pontiac Solstice to make bleeding air out easier with a similar bypass. I ended up installing two inline check valves to make the coolant flow in the proper direction. The cooling system is a lot simpler on the Lehman so controlling direction of flow with check valves will hopefully not be necessary.

If I might chip in to the discussion based on my own experience.
The Ford 2720's are a great engine but like all engines have their own foibles.
Firstly direct seawater cooling is not good for the long life of the engine due to saltwater corrosion or hardwater calcium build up in the cooling circuits.
An indirect cooling system takes sea/river water in through a strainer, from there to an impeller pump which forces the water through a heat exchanger and ejects the water into the exhaust to cool the exhaust pipe before being pumped overboard.
Some points to watch out for.
Always keep the sea water strainer clean to ensure a good flow.
Some people change the impeller every year, its not necessary, mines been in 10 years and is still working perfectly. IF you have a broken impeller be sure to backflush the system to remove any broken pieces.
The engine cooling system is a closed circuit with the heat exchanger instead of a radiator as you would find on a truck.
The secret is to flush your cooling system with a proprietary radiator cleaner until its absolutely clean.
When that's done refill with anti-freeze mixture, even in the tropics, because the anti-freeze contains lubricants to keep your recirculating pump in good condition, it also keeps all the water galleries inside the engine clean and importantly keeps the cylinder liner seals supple.
Simple maintenance that will save you money over the years.

Whgoffrn said:

I've just purchased a 37' trawler with a single lehman 120 and while it runs good now I plan to do maintenance on it and protect from future problems.....from all I've read the Lehman's seem to be good engines as long as you do proper maintenance but 1 common problem I see is cylinder 6 getting hot and destroying piston .....besides making sure there is proper clean oil in the engine and its getting good water and the heat exchangers are working good..... is there any after market products or ways to ensure that #6 cylinder stays cool to protect it?

Click to expand...

You can read what all the people say or you can go directly to the 1 & only expert, American Diesel Corp, in VA. They have a web site.

Brian's dad was involved in the marinization of the Ford engine.

In my mind, he is the ONLY 1 to listen too. They also have PARTS.

Good luck.

Nepidae said:

You can read what all the people say or you can go directly to the 1 & only expert, American Diesel Corp, in VA. They have a web site.

Brian's dad was involved in the marinization of the Ford engine.

In my mind, he is the ONLY 1 to listen too. They also have PARTS.

Good luck.

Click to expand...

What if I told you that Brian would like to hear original questions and not the same question posed by thousands of boaters day in day out.
There are many here that have real world experience and have already talked to Brian and can share that information.
Also, mods made, mods considered can be shared and discussed.
But yes if the answer is not found or trusted here, call AD.

First, unless you are Brian, we'll let him speak for himself. As a business person, THEY USUALLY like to talk to perspective customers. It establishes a relationship.

Second, IF you could be sure that a person's intreptation of an answer could be expressed correctly, then maybe. Why maybe, because a general question could ellicite a different answer under a conversation due to something that wasn't expressed in the question.

Third, someone's mod may not be the best solution. Just because someone made a mod certainly doesn't mean anyone else should.

As to real world experience, well no one here has the real world experience of Brian. He has spent more time with Ford Lehman engines than anyone else here.

He has experienced more real world issue than anyone else here.

You, or anyone else on this forum, or any other, can say what you want.

My opinion, IF you want a verifiable correct answer, call Brian.

I've been dealing with American Diesel for over 25 years. Brian at AD is the undisputed source of knowledge regarding Ford Lehman, as was his father Bob. Brian is extremely helpful to callers and patiently offers great advice.

Having said that, both Brian and Bob have offered conflicting information and advice over the years. Sometimes contradicting each other. And often, advice or information from AD evolve over the years.

The PNW had our own Ford Lehman guru; Norm Dribble at Doc Freemans and later at Pat's Marine Engines. Norm, a diesel and transmission mechanic for over 40 years managed Doc's service department and conducted Ford Lehman seminars annually in Seattle for over 25 years. He was very, very knowledgeable having years of hands on repair experience with Lehmans. He could listen to a cold Lehman starting up with a stethoscope and diagnose a variety of mechanical issues during engine surveys accurately.

Norm Dribble and Bob Smith had many disagreements over Ford Lehman repair, service and maintenance.

It's always wise to seek more than one source for information, advice and solutions and determine for yourself what is correct. Sometimes there are more than one answer or solution.

We are each responsible for the choices we make, whether it is in investing our money or in keeping & maintaining our boats.

Given the choice, I will take Brian's advice over others, regardless.

Joe, Pop or Doc may have worked on a number of Ford Lehman engines, only 1, NOT in that group was involved in the design, Bob.

It isn't surprising that Bob & Brian could disagree. Quite often due to evolution in an area, that 1 sees that the other doesn't, disagreement can arise.

A perfect example was Bob's emphatic position on 30W oil. Even after, and always Rotella, 30W was very hard to find.

Haven't talked to Brian lately about that as I have made my own decision, after consulting with another I feel an expert, in general, and have switched to a Rotella synthetic blend. Main reason, at the time, less than 700hrs on my FL 135's.

Others can voice their experiences, examples, guesses, opinions, and I don't want to discourage that. Maybe my verbiage should have said, after you hear from the forum, check with Brian for his suggestion, then make your own decision. That better?

syjos said:

I bleed that petcock at the high end of the manifold every morning while cruising. I don't know how air gets in there but there is always air present.

An overflow tank will not get air out of the manifold. The petcock is the high spot for air to accumulate. I'm thinking about replacing the petcock on the manifold with a hose barb and connecting it to the bottom of the engines expansion tank with hose which may create a shortcut for air to escape.

Click to expand...

Agreed. An overflow tank would not help. It is a simple check that should be part of checking the coolant.

Take off the fill cap to check the coolant level. You should hear a vacuum that tells you that you have no leaks in your coolant system and it has held a vacuum since the last time it was run (assuming no overflow tank). Add coolant if necessary (which is suspicious) and put the cap back on. Loosen the petcock a tiny bit. Twist it closed when you see coolant rise in the center.

If you do loosen the petcock with the cap off, it might rise too fast and overflow the tiny cavity in the center of the petcock. If it just takes a second for coolant to appear, you likely didn't even have a bubble. If you turn the petcock before checking the fluid level, the vacuum will pull air in and with the fill cap left on it might not bleed properly.

If there is a bubble, it was caused by kraken or marbendlar or something. Who cares? Just get it out.

I haven't looked closely at the slope of the manifold and the inlets to the piston areas, but it seems like a bubble large enough to cause a problem with #6 would be causing problems for other cylinders, just that #6 would likely go first. And calling it a "bubble" probably understates the extent of the lack of coolant in the area.

Marco Flamingo said:

Agreed. An overflow tank would not help. It is a simple check that should be part of checking the coolant.

Take off the fill cap to check the coolant level. You should hear a vacuum that tells you that you have no leaks in your coolant system and it has held a vacuum since the last time it was run (assuming no overflow tank). Add coolant if necessary (which is suspicious) and put the cap back on. Loosen the petcock a tiny bit. Twist it closed when you see coolant rise in the center.

If you do loosen the petcock with the cap off, it might rise too fast and overflow the tiny cavity in the center of the petcock. If it just takes a second for coolant to appear, you likely didn't even have a bubble. If you turn the petcock before checking the fluid level, the vacuum will pull air in and with the fill cap left on it might not bleed properly.

If there is a bubble, it was caused by kraken or marbendlar or something. Who cares? Just get it out.

I haven't looked closely at the slope of the manifold and the inlets to the piston areas, but it seems like a bubble large enough to cause a problem with #6 would be causing problems for other cylinders, just that #6 would likely go first. And calling it a "bubble" probably understates the extent of the lack of coolant in the area.

Click to expand...

What vacuume are you referring to? The cooling system is under pressure while engine is running and maintains that pressure with the thermostati coolant fill cap until the engine cools.

If the petcock is opened first before the cap on a hot engine, coolant will shoot out from pressure. Opening the petcock on a cold engine, coolant appears at the petcock opening after air is expelled but does not spill out.

#6 cylinder is at the low end of the manifold. Any trapped air would migrate to the high point where the petcock resides. And besides, AD has reversed their thinking on the #6 cylinder issue.

syjos said:

What vacuume are you referring to? The cooling system is under pressure while engine is running and maintains that pressure with the thermostati coolant fill cap until the engine cools.

Click to expand...

When it is cooled off (and can be opened for inspection), it has gone from a pressure to a vacuum. The hot layer of air above the coolant has cooled to create a vacuum. Put your ear by the cap and open slowly. It will suck in air if the system has no leaks.

syjos said:

What vacuume are you referring to? The cooling system is under pressure while engine is running and maintains that pressure with the thermostati coolant fill cap until the engine cools.

If the petcock is opened first before the cap on a hot engine, coolant will shoot out from pressure. Opening the petcock on a cold engine, coolant appears at the petcock opening after air is expelled but does not spill out.

#6 cylinder is at the low end of the manifold. Any trapped air would migrate to the high point where the petcock resides. And besides, AD has reversed their thinking on the #6 cylinder issue.

Click to expand...

I think I have to agree about the vacuum. I check expansion tank water level often and find it hard to remove and then it breaks free. As said above, if you are opening the petcock first it would draw in air letting you think there was air in there to start with. Test it by taking off rad cap and then opening petcock.

Nepidae said:

Joe, Pop or Doc may have worked on a number of Ford Lehman engines, only 1, NOT in that group was involved in the design, Bob.

Click to expand...

Clarification. Bob was involved in the design of the marinized parts. Not the engine. Bomac Marine or Logan Diesel rebuild Lehmans as a business. AD sells some marinized parts.

So if you want parts, call Brian. If you want engine knowledge, call Joe, Pop, or Doc.

Sir, I do think Brian Smith knows a thing or two about Lehman engines.

SoWhat said:

Clarification. Bob was involved in the design of the marinized parts. Not the engine. Bomac Marine or Logan Diesel rebuild Lehmans as a business. AD sells some marinized parts.

So if you want parts, call Brian. If you want engine knowledge, call Joe, Pop, or Doc.

Click to expand...

Whgoffrn said:

I talked to the guys at A.D about it and they said it's not nearly as common as what message forums claim....they said when that happens there are other warning signs that are often ignored like other cylinders getting hot first ...kinda makes some sense why would cylinder 1 be 180 and number 6 be 300 yes im sure number 6 can be warmer than the others if clogged but the other cylinders would get warmer also....I talked to them about putting an sensor at #6 and they said that may help but it would be mounted external and have some variances in temp and may or may not be a good indicator if there was a problem...I asked about routing more fluid to 6 and also makes sense that what I route to 6 gets routed away from another cylinder so now I may have new issues at a different cylinder....they said as long as coolant was flushed regularly and I had good water flow and that I paid attention to heat temp gauge I should never have a problem so I guess I'll just go with that...
I may get the expansion tank at some point in hopes that maybe if there was an air bubble in 6 jacket maybe it would come up into the expansion tank....not completely sure I understand how the expansion tank would help serve to eliminate that issue

Click to expand...

You should have a petcock on the fore end of your engine block. Make sure you open that up and take the radiator cap off. You should get Coolant coming out. If not, you have an air bubble. It’s one of my pre-trip checks. I also did the expansion tank replacement. Was pretty simple.

I usta be a big fan of expansion tanks but for years I’ve just check and fill as necessary at the rad cap on top of the exhaust manifold.

Since I have a remote heat exchanger the top half of the exhaust manifold is almost full of coolant. I also have a “Murphy Switch” on the outboard side that is wired to an sound alarm. Saved our skins once at Cape Caution.

If I had an FL I’d provide some way of syphoning off or pumping coolant from the back of #6 cyl. out to the front of the engine probably close to the coolant pump intake. That and adding the hole between the block and head as described previously.

If you get the expansion tank conversion, it will make checking the coolant level a non-issue and you will stop putting coolant in the bilge. The level should now vary over a smaller amount.

Check the dipstick oil level (to make sure its been re-marked) and change the coolant or add to its additives regularly. Service the injectors when they need it and set the valves when the book says. Change the Sims oil at 50 hours or after testing, up to 100 hours. YMMV.

Follow the manual.

Idle before shifting gears, warm up with a load, not over 1200 rpm until warm.

Then repeat regularly for 10 or 20 years.