Ford Lehman 120 Cooling System Air Bleed

psneeld said:

The best way to check for a head gasket compression to coolant leak is with a coolant system pressure tester. At least in my experience.

I had a very sr and experienced lehman mech aboard checking a mystery noise and had mentioned my possible head gasket issue.

He put on a oressure tester and let it build but bleed it off as the engine warmed up. After 20 minutesvor so of running, he showed me how pressure kept building and blowing bubbles through the tubing to the overflow thank.

It confirmed my suspicions, despite the chemical test kit I bought that said all was fine.

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How much pressure build up were you seeing, out of curiosity?

I've completed the test and the gauge stayed at zero, so it looks like I don't have a head gasket problem.

Good news....

I never saw the actual psi range, but any increase after the initial heat expansion would indicate a leak.


The other dead giveaway for me was oil in the coolant and bubbles continuously coming up the tube to the overflow tank.

Took the head to a shop today to be checked and reconditioned. The owner carefully showed me how the combustion was leaking under the gasket.

I was guilty of not retorquing the head regularly due to the variation in older rebuilds and which manual to follow.

Mine is a good example of needing to retorque Lehman 120s every 500 hours or so.

Also do a coolant pressure check. Not a total test to see if head gasket is gone but it should hold a presure. Also check oil for increase in level.

psneeld said:

..I was guilty of not retorquing the head regularly due to the variation in older rebuilds and which manual to follow.
Mine is a good example of needing to retorque Lehman 120s every 500 hours or so.

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I had mine retorqued several months ago, by a thinking slightly nervous mechanic. I think they run more smoothly(hard to be sure with Lehmans) which suggests the retorque improved something, probably head gasket seal.

All possible.

Oil analysis on my engine was perfect for 5 years and 2900 hours.

Just a small combustion to coolant leak at least the last 1000 hours that I chased till now.

Retorque as recommended, every 400 hours or so.

Also, the defects this machinist pointed out showed where the rebuilt Lehman put into my boat just prior to me buying was done by a hack. So buying a boat is a gamble whether due to factory defects, rebuild defects, owner torture tests...etc.... people that like to give advice about buying boats are just guessing at best...no amount of advice guarantees anything...only guarantees.

Unfortunately so true in todays marine field.

Hi, it looks like it (spraying) is caused by engine vibration to me, you can some times get similar results by placing a metal container w/small amount of liquid on top of a running engine.

Greetings,
Mr./Ms. Rog. Welcome aboard!

Hey folks, here's an update.

Took the boat out for a spin. Had a steady 200F on the temp gauges at 1800 RPM (used to see 185F but at least it wasn't climbing). Had 210F on the temp gauges at 2100 RPM.

IR readings at 1800 RPM (with 0.95 emissivity on the gun): 180F on the header tank, and 175F at the temp sensor housing.

IR readings at 2100 RPM: 185F on the header tank, 180F at the temp sensor housing.

The engine has just about cooled down after seven hours (95F on the header tank) and the overflow tank has only dropped a small amount (1 cm), but there was still a bit of air in the system for sure, so that's okay.

For those of you who've taken IR readings of your engine before, are you normally that far out on the numbers (IR vs gauge)? I seem to recall reading that it should only be about five degrees. If that's the case, I'm beginning to think I have a sensor or electrical issue.

Thanks again for all your tips and advice. I think I'm close to knocking this one on the head.

Those are the same IR readings that I have , but 5 degrees more on the gauges.

If your other gauges are accurate, hard to say, but if all off some, usually a voltage issue in your instrument panels or you might have the wrong sender on the engine.

psneeld said:

Those are the same IR readings that I have , but 5 degrees more on the gauges.

If your other gauges are accurate, hard to say, but if all off some, usually a voltage issue in your instrument panels or you might have the wrong sender on the engine.

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Well that's good news then! Time to break out the multimeter. I wanted to re-wire the 12V system on the boat anyway...

Im 10 degrees higher at the helm gauges to ir at the engine.

senangsekali said:

Im 10 degrees higher at the helm gauges to ir at the engine.

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120 Lehman as well? Are your IR readings the same as what I was getting?

Yes 120 lehman. Mine shows 190 195.. but when shooting with ir i have 185 at the cooler. Surveyor showed me where to take temp with ir

For some reason it ran a couple degrees cooler when at wot. Only did that during sea trial for a minute or two.

senangsekali said:

Yes 120 lehman. Mine shows 190 195.. but when shooting with ir i have 185 at the cooler. Surveyor showed me where to take temp with ir

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Roger that. Thanks!

No worries

Oh yeah Mark its me kinslow just so you know.

Another update. I received my Speedseals for the Lehman and my Northern Lights genset. In the process of installing the Speedseal on the Lehman, I pulled the impeller so I could sand off any debris/irregularities on the impeller housing seal face.

Backtracking for a second, the last time I installed the impeller, I wasn't sure if I had got it all the way home. I had not greased the shaft or impeller hub and it was difficult to install. Regardless, it looked like it was 98% of the way in at worst, and the cover sealed properly, so I left it as is.

So going back to this time around, I greased the impeller shaft and hub before reinstalling the impeller, and it popped right in, definitely a mm or two further into the housing than before. I reinstalled the original cover (not the Speedseal, still working out some kinks).

When I fired up the engine, the raw water flow rate out of the exhaust was probably 4x what it was previously; far more than I had ever seen since I acquired the boat. It also ran about five degrees cooler than before, reading about 195F on the gauges at 1800 RPM. It's still warmer than I was used to seeing, but I'll take a five degree drop.

Coolant consumption also appears to be nil.

We're taking off on a week-long trip to the Puget Sound area on Monday. Will be interesting to see how she performs. With everything I'm seeing right now, I'm quite confident that the engine will perform well.