lehman aft freeze plug temps

[pbsurf]

Although the running operating temperatures are within reason at the thermostats, at the other end of the engines, the freeze plugs on the aft end of the cylinder head are at 225 when running at 1600 rpm. Using an infrared thermometer, below the thermostat, port is 170 and starboard is 152. The temps on the port side of block on the freeze plugs are port 150-155, starboard 130-142. The port engine overheated 3 years back and the cylinder head was removed,planed down, new valves, seats and guides replaced, mechanic apparently didn't drain engine as only 3 gallons of coolant was itemized, no thermostats. Mechanic did fit the improved neck in expansion tank for 7lb caps and coolant recovery kit. Engines are 6 cylinder, had 5600 hrs then and now are at 6200. Just replaced both engine raw water impellers. Port coolant removed, engine flushed with fresh till clear then give the drain an enema to get even more sediment out. Port HE removed, put in a bath, visually clean but not pressure tested, new coolant. Brian Smith, at AD, says there is likely sediment in back of the cylinder head that I can scoop out after removing the freeze plug. Want to talk to him a bit more about what the coolant passage is like and recommended tool. Anyone resolve cylinder head aft freeze plug heat before?

 

[Lepke]

Usually the last cylinder runs hotter because it's last in line for coolant. Engine makers try to balance the flow by the size of water passages. 225° isn't too hot. By reducing the size of water ports between the head and block in cylinders 1-5, you can get more coolant to the back. But that can cause problems somewhere else. People building racing engines will modify water passages and ports to better equalize heat and power between cylinders. Even running tubing to the back of the engine. But it's not necessary in yacht engines.
Diesels run more efficiently above 200°, but manufacturers probably run lower thermostats to ward off problems of poor maintenance of the cooling system. I run my diesel pu at 205° and gained about 1+ mile per gallon.
I've never found much sediment in the coolant side of a diesel.

 

[pbsurf]

After removing the heat exchanger I rinsed a fair amount of black sediment off the coolant side of the copper tubes but they were still black, The bath changed them to bare copper.The HE had been tagged with 'serviced 12-2016'. Then 11-2018 I replaced an alternator bracket and forgot to refill the coolant, repaired 4-2019. Ran 600 hrs, mostly short duration, 1/2-2 hours. Figured all was good, maybe it was, maybe not, I don't know. Thankful that this engine is such a sturdy, resilient beast. Having had the cylinder head removed for magnaflux 4 yrs ago, wonder how the coolant passage at the rear freeze plug could have clogged up already.

 

[Comodave]

Keep in mind that Lehmans have a reputation for #6 cylinder overheating. I wouldn’t ignore it.

 

[BruceK]

Keep in mind that Lehmans have a reputation for #6 cylinder overheating. I wouldn’t ignore it.

Famed for it. My mechanic spent a lot of time flushing the block of one of my L120s,eventually excitedly reporting he`d finally cleared it. The sludge could be sitting firm not coloring the coolant. I suggest rinse and repeat with a good coolant system flush product,and recheck the temps. Mine dropped significantly,it became the cooler running engine.

 

[catalinajack]

Although the running operating temperatures are within reason at the thermostats, at the other end of the engines, the freeze plugs on the aft end of the cylinder head are at 225 when running at 1600 rpm. Using an infrared thermometer, below the thermostat, port is 170 and starboard is 152. The temps on the port side of block on the freeze plugs are port 150-155, starboard 130-142. The port engine overheated 3 years back and the cylinder head was removed,planed down, new valves, seats and guides replaced, mechanic apparently didn't drain engine as only 3 gallons of coolant was itemized, no thermostats. Mechanic did fit the improved neck in expansion tank for 7lb caps and coolant recovery kit. Engines are 6 cylinder, had 5600 hrs then and now are at 6200. Just replaced both engine raw water impellers. Port coolant removed, engine flushed with fresh till clear then give the drain an enema to get even more sediment out. Port HE removed, put in a bath, visually clean but not pressure tested, new coolant. Brian Smith, at AD, says there is likely sediment in back of the cylinder head that I can scoop out after removing the freeze plug. Want to talk to him a bit more about what the coolant passage is like and recommended tool. Anyone resolve cylinder head aft freeze plug heat before?

Your engines are running way, way too cool. You need new 180-degree thermostats. Get them from American Diesel or get a simple 53mm Stant thermostat ($10?) and drill a 1/8-inch hole in the horizontal surface which acts an an internal air bleed. The AD unit will have this hole.

 

[pbsurf]

New understanding of situation, Brian Smith informed me that I am measuring the exhaust gas heat at the aft cylinder head freeze plug, not the coolant. The coolant freeze plug is below it on the block on the level of the heat exchanger. The measurements made on freeze plugs on port side of block indicate I don't have a heat issue. It is a running cold issue. Sometimes I feel blind to what is in front of me, so good to have ears. Brian is super patient and helpful. Suggests that my infrared gun isn't reading accurately because if my engines were actually that cold, they would be hard starting, not 2-3 seconds and there would be a lot of smoke. Running 1460 rpm port reading below thermostat is 170 no smoke, starboard 153 and minor smoke noted. Something else he mentioned is that the pre-'74 Lehmans don't have a #6 cylinder overheat issue as likely as #1 and 2. Planning to get new temp readings with different gun as well as draining starboard coolant, rinse, refill w/new as I don't know when it was done last.

 

[Comodave]

Gotta love Brian. When we had Lehmans he was excellent in his support.

 

[hytedin]

Agreed!