Ford Lehman 120

I don't have a problem. Been running all summer, almost 2000 miles so far. No problems with the engine.
Been running 1600 to 1700 rpm at cruise, adding a little oil now and then. Been changing inj pump oil atr 75 hours, changed engine oil at 200+.
Averaging "about" 1.88 gal per hour, almost 3.5 miles per gallon (statute miles). That includes gen time, but only maybe 20 hours or so.

Now if I can only remember how to open the fuel cap before winter storage.......

Great, good for you, nice to heara positive story on here.

I`ve a problem with the hose between the manifold and heat exchanger flattening itself or sucking in on itself on my FL 120s. Part number is 3K503. Both have been replaced with the 90 degree bend section cut from a hose for a Ford car engine. The port engine had same the problem at survey 2.5 years ago,I replaced it, leaving a presumed mild steel spring coil inside in place.
I replaced the starboard one a few weeks back for the same reason,this time removing the spring. Today, with the engine not being run,it is again flattened off.
I ran the boat 4 days ago for over 3 hours, mostly at 1500=1600rpm,with no change in displayed temperatures,or any other apparent issue.On checking the port one is slightly flattened ,but less so. It occurs to me as I type this maybe I should recheck with engines running to see if they resume normal shape then.
The heat exchangers were renewed under a year ago.At the same time I replaced the oil coolers and exhaust elbows. I recently replaced the coolant tank caps with new ones supplied by AD and since then the engines lose less coolant in overflow.Engines are just under 2000 hours and running well.
Any thoughts why this is happening? BruceK

On the engines themselves we use coolant and raw water hoses supplied by American Diesel and have never had a problem.

When we had big sea strainers installed on the boat after it was offloaded from the truck in a yard in Tacoma I noticed after we started using the boat that the hose from the port sea strainer to the raw water pump (installed by the yard) was flattened out when the engine was running at cruise rpm. Called the diesel shop in Bellingham and they replaced the hose with a "proper" wire-reinforced hose. No more collapsing problem after that and that was 14 years ago.

Following Marin`s post I emailed American Diesel; I trust they will not mind me quoting Brian Smith`s helpful prompt reply:

"...the entire fresh water(closed)system of your engine is under suction from the fresh water circulation pump. It is critical that the molded hoses have spring inserts to prevent them from drawing shut when the engine is running"

(AD can supply all the hoses,individually or as a full kit.)

I removed the spring insert when replacing the starboard hose because my (then) shipwright advised not leaving it in, as I did on the port engine.
Lehman owners, ensure your hoses are not drawing shut and are supported by spring inserts. In the short term I will buy another Ford hose to cut out a spring supported right angle bend, before operating the engine again. BruceK

Aussie FL120 operators, a radiator hose from which you can cut the section for this hose is a Ford Falcon EA/Fairlane NA bottom hose. It has the internal spring support. Readily available at auto parts shops. Bruce K

BruceK said:

"...the entire fresh water(closed)system of your engine is under suction from the fresh water circulation pump. It is critical that the molded hoses have spring inserts to prevent them from drawing shut when the engine is running"

Click to expand...

If that were the case you could leave the "radiator cap" off and increase the temperature limit of your coolant. Or conversely, you could remove the cap while the engine is hot and running and not have a worry in the world about blowing hot coolant all over yourself and the engine room.

There is a pressure differential on either side of the pump, after all that is what a pump does, it creates a pressure differential to move fluid. But, once the engine warms up the entire system is well above atmospheric pressure. What we call "suction" and the force that collapses the hose is the difference between the pressure inside the hose and where you are standing to look at it.

The flow of coolant in your engine is from the header tank to the heat exchanger, to the manifold, then on to the suction side of the fresh water pump. Unless you have a serious flow restriction in the heat exchanger there is no way the pressure between the heat exchanger and the manifold can go below atmospheric when that engine is hot. If it did your coolant would flash into steam at reduced pressure, most likely at the pump itself and all the pressure differential would vanish.

I believe that you will find that you simply have a well sealed fresh water circuit and when the engine cools a slight vacuum is formed in the system. I bet that if you remove your radiator cap when the engine has cooled enough to do it safely and leave it loose you will probably not see a collapsed hose.

Does your radiator cap have a vacuum breaker or overflow tank fitted and does coolant flow in and out of the tank?

As far as replacing the spring, I think that is a good idea for no other reason than a hose that continually collapses will eventually delaminate and fail when under pressure.