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Old 07-30-2011, 06:56 PM   #1
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120 Lehman overheating

I was out for a cruise today and the*120 lehman*appeared to be running hot.* The gauges were reading about 210 but when I dropped the rpms*down for awhile it cooled to 180.* I*just had a lot of electrical work done so I thought the different reading might be a result*of the rewiring.* *In any case when I got back to home port it was definitely hot and when I checked the engine it had indeed blown out some coolant.

I had the heat exchanger replaced this spring and in hindsight i think it may have been running hot ever since.* Today I noticed more steam than normal and a slightly different tone to the exhaust.* It was still pumping out water thouogh.

I've noticed on the forumm that the lehman raw water pump design is flawed.* What's the best way to check if the water pump is my problem?* Versus perhaps a thermostat?* If it is the pump can i just replace the impeller?

I've dropped a few extra boat units this year and of course this problem is occuring the week before we were planning our family vacation on the boat.*

Thanks!

Tom

*

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Old 07-30-2011, 08:09 PM   #2
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120 Lehman overheating

The stock Jabsco raw water pump is not the problem. The stock Lehman-designed raw water pump drive coupler is. It has a fatal flaw in its design and manufacture but it either works or it's failed. There is no middle ground. And when it fails the raw water pump stops turning right now. So from your description of the problem the Lehman drive coupler (if your engine is still equipped with the stock raw water system) is not the cause of the problem.

There are a number of things that can cause overheating in an FL120 (or other simiilar engine). The ones we've encountered so far are:

1. Leaking coolant pump. As on a vehicle, these pumps have a finite life and when the seal(s) go the pump begins to leak or blow coolant.
2. Collapsed raw water hose. If the raw water hose leading to the raw water pump is old, soft, or of the wrong type, the suction from the pump can cause it to partially or completely collapse. But when the pump is not running the hose will appear normal.
3. Blocked or partially blocked raw water intake. This can occur for a number of reasons--- barnacles or other growth, grass/weed that's been sucked up into and jammed inside the through-hull, too much bottom paint on the external strainer (f your boat is so equipped) that's closed down the holes or slots. We've even experienced a weird, crystalline growth that gradually closed off the port raw water through-hull to the point where the engine began to run hot. The diesel shop had to chip it out with a screwdriver. They said they'd seen it only a few times before, and the timing was such that it had obviously been "growing" in the through-hull before we bought the boat. Whatever it was, it has never come back.

Other causes could be:
1. A partially blocked heat exchanger--- main, lube oil, or transmission fluid.
2. A partially blocked or delaminated and collapsing raw water hose between the various heat exchangers.
3. A failing or failed thermostat that is no longer opening up enough when the coolant gets hot.
4. A worn raw water pump (the Jabsco unit on the end of the drive coupler). Problems could be a failing impeller or a too-loose fit between the cover plate and the front surface of the impeller and the wear plate and the rear surface of the impeller. If the impeller is not a tight fit between the cover and wear plates, it in effect loses "compression" and the water flow will be reduced. It will still pump water but perhaps not enough to keep the coolant temp where it should be. If this turns out to be the problem the pump can be overhauled with a new impeller, cover and wear plates, and bearing/seal. In fact I believe this pump is still available new off the shelf from Jabsco.

However.... are you SURE the engine is actually running too hot? A coolant temperature gauge reading can vary with the resistance in the line connecting it to the sensor or ground. Also, the temp sensor itself could be a bit flaky. This is NOT to say that you should assume it's the gauge or the sensor and continue running the engine as-is. The fastest way to kill a Ford Lehman 120 is to overheat it. Even for just a few minutes. The head gasket will go right now followed by the head warping and there is also a risk of severe cylinder wall damage. I have heard this directly from people in the UK with decades of experience with the base engine (Ford of England Dover engine) in trucks and industrial and agricultural applications.

We have had three precautionary engine shutdowns in the thirteen years we've owned the boat, each of them due to cooling issues. One was a leaking coolant pump that gradually dumped coolant into the drip pan during our first run with the boat from Tacoma to Bellingham after we'd had the boat trucked north from California. The other two were due to blockages of the raw water intake through-hull. In each case as soon as we noticed the coolant temperature starting to climb we shut the engine down, tied off the shaft, and finished the trip on the other engine.

Learning the FL120s vulnerability to overheating is what prompted us to adapt the use of a small oven timer at the helm set for a five minute countdown. The timer beeps, and whoever is at the helm scans the engine instruments and then puhes the restart button on the timer. It's too easy to get distracted when running a boat and looking out the windows or at the nav equipment or talking to friends and a long period of time can go by between engine gauge checks. Sure, the FL120 has oil pressure and coolant temperature alarms but I learned a long time ago that the purpose of an alarm is to let you know that the piece of equipment the alarm is monitoring has just failed. I got the idea of the timer from two places--- Carey of this forum does the same thing and the trans-Australian railroad. We also put thin pieces of black tape on each instrument (except the tachs) matching the normal indication of that particular gauge. That way the briefest of glances tells the helmsperson if a reading is off.

You can get as sophisticated about this as you want. A number of people on the Grand Banks owners forum have installed raw water flow alarms on their boats. Some have temperature sensors on their oil, transmission, and main engine heat exchangers. These are all great ideas. I've just not been motivated enough to make the effort, hence the oven timer :-)

One thing I don't know that RickB or someone might be able to tell me is if the EGTs (pyrometers) on our boat would be of any value as overheat indicators. I'm inclined to think not as the change in the EGT readings might be too subtle to mean anything until it's way too late.

PS--- I want to add that, regardless of what suggestions I or anyone else on an internet forum gives you, an overheat situation is not something to be taken lightly.* It is my opinon that unless one is well aquainted with their engine's systems and is real good at troubleshooting, the problem is best turned over to an experienced and reputable pro.


-- Edited by Marin on Saturday 30th of July 2011 08:43:46 PM
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Old 07-30-2011, 10:27 PM   #3
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RE: 120 Lehman overheating

To add to Marin's post,
  1. What RPMs do y ou normally run and what RPMs did overheat occur?
  2. Overpropped, can't achieve full RPM, bottom and prop *clean issues?
  3. Remove and clean*your sea strainer in front of the engine
  4. Is your raw water flow restricted at the exhaust elbow*- how old is the elbow
  5. Buy and IR gun and use it to check temps in 6 or so places on a routine basis
  6. More details regarding routine cooling system maintenance actions and when (during the past 12* months) would be helpful
  7. Have you ever used Ridlyme or similar product to* clean the HX and cooling system?
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Old 07-31-2011, 05:11 AM   #4
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RE: 120 Lehman overheating

Diesel exhaust temperature is an excellent indicator of engine load but isn't of much value for monitoring coolant or oil temperature.

To eliminate the chance of confusing terms, EGT is normally measured in the exhaust gas path as near to the exhaust valve as practical. Installations that use a separate probe for each cylinder sometimes include a graphic display and even alarm to indicate temperature variations between cylinders or abnormally high temperature. A single EGT probe might be mounted at some point where the gases from all cylinders are combined, such as just before the turbocharger if one is fitted. This is also called turbine inlet temperature or TIT. If the probe is mounted on the outlet elbow of the turbo, it is called turbine outlet temperature or TOT.

No matter where the probe is mounted, the temperature is directly related to the amount of fuel being burned in the cylinder, and by extension, the load on the engine or a single cylinder. Because load can change considerably, so can exhaust temperature. A heavily loaded engine might show around 1000F or 500C depending on where the probe is located, a lightly loaded engine might only show a few hundred. The range is so wide and so dependent on small changes in load and where the probe is located that temperatures high enough to destroy the engine are lost in the "noise" of normal operation.

As Marin mentioned, the temp indication itself could be faulty. If you have an oil temperature gauge, use that as a cross reference. If oil temperature rises abnormally along with coolant temperature then there is most likely a problem. A temperature switch mounted externally on the exhaust elbow near the spray ring can warn you of a loss of raw water flow, hopefully (most likely) before the engine is damaged but is not much help if there are any of the many other problems that can cause general overheating of the engine.
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Old 07-31-2011, 06:54 AM   #5
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RE: 120 Lehman overheating

Thanks Guys!

Marin that's a particularly comprehensive response!

Notes:

Gauges were reading around 210at a high, maybe 230 when I reached home port and temp did not come down at idle (hope I didn't damage engine)

I was cruising at 6-7 knots which is normal, tachs read 2500 RPM at this speed (but may read high)

Never used Ridlyme (how do you use it?)

Not sure of exhaust elbow age I've had boat 5 years and not replaced it.* There is a slight drip below the elbow that drips onto the heat exchanger.* This is where the heat exchanger originally*corroded through.

I have no oil temp gauges to cross reference but when I got close to home where it was hottest the oil pressure gauges began to "blink" witht he needle jumping around a bit (but still at 35-40 lbs)

Recent maintenance:

Replaced heat exchanger and trans cooler this Spring and zincs

Serviced raw water seacock this Spring, disassemble clean/lube

Cleaned raw water strainer this Spring (did not remove from boat so not sure if there could have been debris between strainer and through hull) I use zinc spray paint on the strainer so there is no bottom paint build up

Hoses are ~3 years old, appear good

Temp gauges and 2 gauge sender are ~ 3 yrs old

Thermostat is also ~ 3 yrs old

Next Actions:

Refill coolant, it definitely overheated*(I hope I didnt incur engine damage)

Run and check temp at idle

Recheck hoses under load

Check circulating pump for leaks

Don't think it's the drive coupler Thanks to Marin's comment

Don't think it's the t-stat since it was cooling at low RPM's

Questions:

At what temp does one cause engine damage?

Suspect it's the pump, how can I confirm low water flow?

Thanks again Guys!

*
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Old 07-31-2011, 07:28 AM   #6
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RE: 120 Lehman overheating

could be that the oil cooler might be pluged up with somthing, the raw water from the pump goes to the oil cooler first before it entrs the engine,
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Old 07-31-2011, 08:36 AM   #7
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120 Lehman overheating

2500 RPM (verify with photo tach) at 7 knots? At 7 knots most trawlers are only about 1600 to 1900 with a Lehman 120.* Exhaust elbow dripping, YIKES!

It sounds like Marin nailed it in your case, "get an expert." Call Bob Smith at American diesel for a*reference in your area.*No matter what the current issue is, engage this guy for the long term - marine diesels need constant attention.

To really nail down your RW water flows, there are vacuum and pressure gauges for checking this -"Yup, I've got water," isn't enough. Damage potential you ask, Lehmans are*forgiving but ------ a Cat would likely be fried given your stated conditions.

Also, go to boatdiesel.com, pay the $25 and search the archives for:
<ul>[*]Lehman[*]Cooling system (Good point by Jerry on transmission cooler)[*]Overheat[*]Ridlyme[*]HX or heat exchanger[*]Exhaust elbow or shower head[*]Engine loading[*]RPM[*]Impeller[*]Raw water pump[*]Photo tach[*]IR gun (use it to* shoot your pan for oil temperature)[*]EGT[/list]*


-- Edited by sunchaser on Sunday 31st of July 2011 08:43:24 AM
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Old 07-31-2011, 12:22 PM   #8
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RE: 120 Lehman overheating

OK here's this morning's report:
I filled the coolant, it took 2 gallons
Checked raw water seacock for proper operation
Ran at fast idle for 40 mins and temp didn't rise above 170
Thermostat opened and coolant was flowing
Ran for an hour at 6-7 knots and temp did not rise above ~190
Idling back to mooring temp dropped back down to 170
No leaks form circulating pump
All hoses look good, no leaks at any connections
Raw water intake elbow cool to touch
Exhaust water warm to touch (about the temperature of hot shower)
I'm waiting for it to cool down and I'll check the expansion tank for coolant loss

I've called a local mechanic to replace the impeller as a next step.
I'll pick up an IR temp gun as well.

I had the heat exchanger and trans cooler replaced this year but not the oil cooler

Any additional thoughts-advice are appreciated

Thanks Gentlemen,

Tom
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Old 07-31-2011, 01:16 PM   #9
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RE: 120 Lehman overheating

Ask your mechanic if he will walk you through and you can watch the impeller change.* It's not an overly complicated procedure, but, much easier to learn if you watch and take notes.* It's something we should all know how to do, as rare as an unscheduled failure can be.

The benefit of knowing how to change an impeller*is that it's one of the first places to look in your current situation and if you carry a spare, you can save yourself a long tow home for a relatively simple failure.

cheers,
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Old 07-31-2011, 02:41 PM   #10
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120 Lehman overheating

Not sure if this was mentioned before, but prehaps the belt driving the alternator and fresh water circulator pump is loose and slipping?

The drip from the bottom of the exhaust elbow could be an indication it has cracked or is about to rust thru.* This will be a big problem if it decides to let go (at the wrong time) and cause you to have to shut down your engine.

Whenever you service your cooling system you have to bleed the air out of the high side of the exhaust manifold, or it will airlock and cause overheating.

While the engine is cool and not running, open the petcock on the top of the manifold and add coolant to the expansion tank until solid coolant (no air bubbles)emerges from the petcock, then close it.

JohnP


-- Edited by JohnP on Sunday 31st of July 2011 02:45:37 PM
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Old 07-31-2011, 04:55 PM   #11
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RE: 120 Lehman overheating

Thanks Kevin-John,

I'm pretty sure I could handle the repair, and was ready to dig into it today, but I didn't want to chance incapacitating the boat on the mooring for lack of parts/tools/expertise. I will watch and learn whe I get a mechanic here.

The belt is tight and driving the circulating pump.

I never bled the air out of the system after the heat exchanger/trans cooler were replaced. So definitely going to try that ASAP - Thanks for the idea! I did top off the system a couple of times. Could an airlock cause the conditions I'm experiencing or would it be an "all or nothing" kind of overheating?

Thanks

Tom
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Old 07-31-2011, 07:00 PM   #12
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RE: 120 Lehman overheating

redo the water pump anyhow as a matter of service then you know its good
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Old 07-31-2011, 07:02 PM   #13
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RE: 120 Lehman overheating

"I filled the coolant, it took 2 gallons"

That's a lot of water you have lost from a closed loop fresh water cooling system. From my understanding of the Lehman 120, the engine does'nt take more than a couple of gallons or so in total, so you have lost a fair proportion of your fresh water coolant. The question then is where did it go & how did it get out?

I have just had a similar problem on my Lehman losing fresh water coolant, having to top up the sysytem regularly only to find it sitting in the drip tray below the engine. The problem turned out to be a slightly warped manifold and end caps, once they were taken off and machined that fixed the problem. Not as expensive as it sounds. This may not be your problem but it's worth crossing off the list.

Good luck.

PS Regarding the petcock that John P mentioned, we once bled the system and did'nt tighten it up properly and lost most of the coolant , the engine temp rose to 220+ in a very short time.Something tokeep in mind.
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Old 08-01-2011, 06:22 AM   #14
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RE: 120 Lehman overheating

Quote:
tomtomterrific wrote:
Thanks Kevin-John,
*Could an airlock cause the conditions I'm experiencing or would it be an "all or nothing" kind of overheating?

Thanks

Tom
**********It could be the cause of your problem-- that would be an easy fix.

********* JohnP
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Old 08-01-2011, 07:16 AM   #15
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RE: 120 Lehman overheating

Opened the petcock and filled the expansion tank. No air or bubbles just coolant bleeding out.

So I'll cross that one off the list. So much for the easy fix

So, I'm down to replacing the imnpeller and checking the oil cooler for obstruction.

What temps do you guys get on a 120 Lehman?*

As I mentioned after refilling and rechecking everything, after the overheating incident, I cruised for an hour at 7 knots and the gauges read 190.

I don't think it "fixed itself" but perhaps could have had a temporary obstruction or airlock then.

I plan on getting the raw water pump rebuilt anyway.

Thanks,

Tom
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Old 08-01-2011, 07:43 AM   #16
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RE: 120 Lehman overheating

As noted by previous posts, two*questions are relevant, where is the coolant going and why?

Did it all end up in your over flow, is it leaking out through a HX, is it going out through a bad head or manifold due to gasket or crack? The why part you are diligently (good work on your part) chasing down. Don't forget plugged*flow potential from strainer to exhaust elbow.

Both where and why need answers or event will most likely occur again. You are not alone, many of us have suffered and chased overheat issues. My experience with Cats is a mild overheat can*lead to a cracked head, with the where and why questions requiring resolution

Last but not least, do you really cruise at 2500 RPM? If not, what RPM? On many vessels (usually not slow trawlers), overheats are a result of dirty props/*bottom and wrong props with resultant over loading.
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Old 08-01-2011, 07:59 AM   #17
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RE: 120 Lehman overheating

Quote:
tomtomterrific wrote:
What temps do you guys get on a 120 Lehman?*

As I mentioned after refilling and rechecking everything, after the overheating incident, I cruised for an hour at 7 knots and the gauges read 190.
*The "guru" Bob Smith says to install a mechanical temp gage at the bottom of the expansion tank and that should read 170 F. The previous owner of my boat had done that and that gage (gage is located in the engine room) reads 170 to 175 evey time I have looked at it. At the same time my electric temp gages (which I replaced along with the sender 2 years ago) read 180/185 ish.* That would be at my normal cruise rpm which is 1750/1800 rpm (on a calibrated tach) and I'm usually running right around 7 knots depending upon conditions.

When I push her up to 2500 which I do from time to time the electric temp gages go up to 195 ish, maybe 200 (hard to tell exactly) and hold there, returning pretty quickly to the*180 range once I back down.

*
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Old 08-01-2011, 09:53 AM   #18
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RE: 120 Lehman overheating

TG,

On the "where" question, it overheated and spewed out the 4# pressurized *cap, ending up in the bilge.

On my cruise after I refilled the cooland and rechecked everything, it ran at 190 for*an hour @ 7 knots and I found no leaks at the circulating pump or any hose connections.* Also no*coolant loss checking the expansion tank after it cooled down.

Regarding my*"2500 RPM" - the tachs are not calibrated and I assume this is really ~1700-1800 RPM.*

If it is a bad head gasket/cracked head-manifold what other symptoms should I look for?

I like the idea of a mechanical temp gauge and I'm putting an IR heat gun and a photo tach on my Christmas list!* I suppose I can use a meat hermometer in the meantime

Thanks,

Tom
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Old 08-01-2011, 11:02 AM   #19
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RE: 120 Lehman overheating

Quote:
tomtomterrific wrote:
TG,

On the "where" question, it overheated and spewed out the 4# pressurized *cap, ending up in the bilge.

Regarding my*"2500 RPM" - the tachs are not calibrated and I assume this is really ~1700-1800 RPM.*

I like the idea of a mechanical temp gauge and I'm putting an IR heat gun and a photo tach on my Christmas list!* I suppose I can use a meat hermometer in the meantime

Thanks,

Tom
*Have you ever replaced the "radiator" cap on the expansion tank? Old caps that do not regulate pressure properly can cause problems. I just put a new one on mine this spring as a mainteance item. Cheap. insurance.
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Old 08-01-2011, 11:28 AM   #20
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RE: 120 Lehman overheating

Yes the 4# cap is new this Spring.** It's made in Mexico and seems inferior to*the "old" one I took off.* I'm assuming the "guts" (spring and gasket) are good though.
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