John Deere 6068 runs hot when opened up

Downrigga

Admiral
Joined
Mar 25, 2016
Posts
5,026
Likes
5,787
Location
Harwichport MA
Boat Make
36' NB
I thought about it last winter but Art Stanley disagrees, and he maintains her. We have gone threw just about everything. Her hoses have been replaced, t-stats replaced 180 degrees (more than once), second temp prob and mechanical gauge added, (alarm set to go off before engine alarm does) electrical temp prob replaced. new raw water pump for other reasons, new engine circulation pump, new heat exchanger, after cooler cleaned, new belt and air filter. Intake and seacock inspected and cleaned. Engine flushed and coolant replaced with John Deere cool guard. Prop is spot on when at 100 present load. The goose neck bushing in front of engine going into heat exchanged checked. Inner "freeze plugs in heat exchanger bundle checked and replaced. Hydraulic cooler cleaned and gear cooler replaced. Wet elbow checked. At 2200, cruising at 15mph I am at 205 after ten minutes.
What kind of boat is this ?
 

Johnny Jet

Deckhand
Joined
Jul 15, 2022
Posts
1
Likes
0
First Name
John
Been chasing this problem for two seasons now. I have a 6068SFM50 rated at 265 hp. Wheel is spot on and I turn 2500 rpms at 100 present load. Hull bottom is spotless and intakes are clean. I normally run 2000 to 2100 rpms, temp will be 187 / 190. As I increase the throttle I start to climb temperature. If I run 2400 for any amount of time (10 minutes or more) I hit 200 degrees, Run wide open i hit 207. Alarm trips at 210 so i back off. Over the winter I replaced the raw water pump (bad shaft) heat exchanger and installed two new 185 degree themostats, replaced any hose that was questionable, air temp and coolant sensors replaced. Running John Deere cool guard antifreeze. Engine circulator pump seem good. Aftercooler cleaned late last season as well as hydraulic cooler cleaned at same time and gear cooler has been replaced. Spend two hours with a very well respected mechanic on board today running up down the harbor trying to figure it out. Pulled hoses at different points to check flow. Coolant system was pressure tested again. We are stumped, any ideas would be great. Thanks guys.
I had a very similar problem with a Westerbeke 50 hp diesel in my cape dory trawler. Wound up replacing a lot like you with no improvement. Laser heat gun on engine coolant at differen locations said temps were fine. Finally, replaced the Temp gauge on the instrument panel and lo & behold Temp stayed in the middle of the green arc!
 

Saltydoc58

1st Mate
Joined
Oct 8, 2020
Posts
288
Likes
220
Location
Lloyd Neck, NY
First Name
Robert
Boat Make
Ellis 28 Yanmar 6LPA STP 315HP, Parker 1801 Yamaha F115
It may have been stated or addressed already..... but make sure the impeller is not spinning on it's spline. Some aftermarket impellers "look good" on inspection and work at low speed, then spin off at higher RPMs causing overheating due to inadequate flow. You have to remove it and carefully check for that.

Also as mentioned a flow meter installed somewhere along the line may be helpful to assess raw water cooling flow.

Keep us posted as this is a problem that we all may need to troubleshoot someday.
 

BigD25

Deckhand
Joined
Mar 27, 2018
Posts
1
Likes
3
Age
73
Location
Ontario, Canada
Boat Make
33 Egg Harbor SF ('72) and a Stanley 16W
I had a very similar problem with a Westerbeke 50 hp diesel in my cape dory trawler. Wound up replacing a lot like you with no improvement. Laser heat gun on engine coolant at differen locations said temps were fine. Finally, replaced the Temp gauge on the instrument panel and lo & behold Temp stayed in the middle of the green arc!
What kind of boat is this ?
Salt water is the worst on heat exchangers. Have you "descaled" the heat exchanger? A very thin layer of calcification\salt has serious effect on heat transfer. I have been descaling heat exchangers in over 40 years of my trade when high temperatures and pressures cause shutdowns. Typically a submersible 120 volt "acid pump" in a 5 gallon bucket is used in pumping the solution into one end of the Hx and a hose dumping the outlet back into the bucket. Some descaling products change color when the the solution is nuetralized while others you must us litmus paper to test. Two years ago I had issues on my "fresh water" Hx. Descaling did the trick. Now running 190 degrees constantly under any load. Always use an "inhibited" descaler that does NOT attack the metal. Hydrochloric acid will be the main constituent but it MUST be inhibited. NEVER use anything to do with sulfuric acid. There is also "pacifiers" that chemically protect the metal after descaling from corrosion/rust. Anyway that's my two cents from 40 years of reconditioning heat exchangers. Hope this helps.
 

Super typhoon

Deckhand
Joined
Jul 24, 2022
Posts
15
Likes
5
Location
Nieuwpoort, Belgium, Southern North Sea
First Name
Robert
Boat Make
Starfish 10
Thank you for your reply BigD25. Happy to see that you're running 190°F under any load. That's just the temperature where the alarm switch off, on Perkins engines !
Have you already used vinegar to clean heat exchangers (in copper) ?
Did you also descale blocks and head with hydrochloric acid ?
 

proskirichard

1st Mate
Joined
Aug 21, 2013
Posts
121
Likes
46
To increase the boiling point of the coolant the cooling has a pressure cap. Each pound of pressure raises the boiling point of the coolant by 3 degrees I saw your post and you pressure checked the cooling system did you check the cap? You might also want to check if its the right cap for your application ( right amount of pressure 8, 10, 12, 14, 16 etc. I had a problem with a cummins a few years back. It turned out the cap was incorrect and defective too. Good luck
 

Captinlon

1st Mate
Joined
Mar 28, 2016
Posts
492
Likes
315
Location
Coast of Maine
Boat Make
32 H & H
To increase the boiling point of the coolant the cooling has a pressure cap. Each pound of pressure raises the boiling point of the coolant by 3 degrees I saw your post and you pressure checked the cooling system did you check the cap? You might also want to check if its the right cap for your application ( right amount of pressure 8, 10, 12, 14, 16 etc. I had a problem with a cummins a few years back. It turned out the cap was incorrect and defective too. Good luck
pressure tested and cap replaced with new jd cap
 

andy65

1st Mate
Joined
Feb 11, 2012
Posts
497
Likes
450
First Name
Andy
Boat Make
Northern Bay 36
make sure the impeller is not spinning on it's spline. Some aftermarket impellers "look good" on inspection and work at low speed, then spin off at higher RPMs causing overheating due to inadequate flow
That happened to me with two new Sierra impellers on a prior boat. Also saw a situation where the impeller housing was worn, virtually invisible to the naked eye, causing poor flow. And a case where flow was reduced in a cast housing due to scale. A flow meter is a must check. Is your pump gear or belt driven?
 

proskirichard

1st Mate
Joined
Aug 21, 2013
Posts
121
Likes
46
There is a test kit you can get to test the engine coolant for combustion gases in the coolant. It would help confirm or eliminate a head gasket issue.
 

TxMike

Deckhand
Joined
Apr 22, 2022
Posts
8
Likes
2
First Name
Mike
Bubbles in your overflow tank @ WOT? If you don't have one, put your overflow hose in a jar of water and look for bubbles @ WOT.
You will get some bubbles out as it warms and cools for a couple of cycles but after that bubbles @ WOT mean head gasket. Also you can purchase a test kit to look for combustion byproducts in your coolant. Try NAPA.
Yup
 

fellsptmariner

Deckhand
Joined
Jan 22, 2020
Posts
86
Likes
21
Location
Baltimore
Boat Make
Custom 57'
I've been watching this post with some interest...I have recently re powered with a mechanical 6068 rated 225hp. The topic of these engines running on the hot side seems to come up in forum threads from time to time. Since I haven't put mine in service yet I have no real time experience to share -however - I have been thinking about the subject for some time...

...so what if you would tap off the the freshwater circulation and run lines to a heat exchanged type cabin heater or hot water heater -or both and in doing so increase the water/glycol capacity of the cooling system at the same time shedding some temperature in the exchange. One could hope for a drop of at least 10 degrees in the process and perhaps get the block temps back down to 190 levels at higher rpms.

The older 6068 's like mine came in 3 factory rated versions from 175 to 225 hp. The difference in hp is created by different fuel injector pumps each set to deliver a specific flow to the engine. More fuel - more heat. WOT on these versions ranged from 2400 -2600 respectively.

The newer computer controlled versions are pumping out more fuel to up the hp ratings and dealing with more heat in the process. If the OP of this thread doesn't use or need the additional hp - I would think a Deere tech could bring his laptop on board and dial down the injector pump to a fuel delivery level that would not effect top end rpms but would decrease fuel consumption and hp in the process - thus possibly allowing the engine to run cooler.
 


Latest Posts

Top Bottom