Overheated Diesel -- What Damage to Look For? - SailNet Community
LinkBack Thread Tools
post #1 of 10 Old 02-20-2010 Thread Starter
Senior Member
FishFinder's Avatar
Join Date: Feb 2008
Posts: 139
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 13
Overheated Diesel -- What Damage to Look For?

I overheated my 1980 Volvo MD7A yesterday -- I think the raw water intake clogged with debris I'm not totally sure yet. But whatever happened, it happened suddenly. Engine was running fine then it sounded different and the temperature gauge was pegged in the red. I shut down as soon as I noticed the problem and got a tow back in, but the engine was probably overheated for say 5-10 minutes prior to shutdown. There was a little smoke in the engine bay.

What kind of damage should I look for now in the engine? I'm going to go through the cooling system and clean it out/replace impeller etc. but I'm more worried about bigger issues ... any thoughts?

1980 S2 9.2A (30') in Anacortes, WA
Aux power 13hp Volvo MD7A
FishFinder is offline  
Sponsored Links
post #2 of 10 Old 02-20-2010
Handsome devil
Stillraining's Avatar
Join Date: Jan 2008
Location: LaConner,Washington
Posts: 3,477
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 15
Its a crap shoot...anything form lucking out and nothing happening to a cracked/warped head and or melted pistons cracked rings and scored cylinder walls.

Do your investigation and try and find the cause first...bad impeller etc....and during that investigation check your cooling system for any trace of oil ...and your oil system for any trace of water a good sign right off the bat of either a head gasket or cracked head....BUMMER!

First you will want to install a new thermostat never trust one that has been subjected to an overheating...its cheap insurance.

Then if it was my engine I would pull the glow plugs and spin the engine to see if any water were in any of the cylinders...you wont harm a rod if the water has someplace to go if indeed you took out a head gasket or cracked a head and its letting water into one or more cylinders.

If all is good and you corrected any cooling system blockage...Put the Glow plugs back in and I would try and start her with out the heat exchanger cap on.....check for any bad sound from your engine if it sounds bad shut it down...BUMMER..Piston problums....If it sound good immediately monitor your exhaust for both proper cooling water flow and steam ....If there is steam comming out you have a head gasket or a cracked/ warped head...BUMMER...if not go to the next step your not in the clear yet.

Let the engine come up to operating temp...once the thermostat is opened peer into your heat exchanger...if it has gas bubbles, a funny smell or is violently rolling...You have a blown head gasket or a cracked head...BUMMER!...If all is well go to the next step your not out of the woods yet.

Put the cap back on the heat exchanger and put a load on the engine for 10 or 15 min...you can do this right at the dock in gear with good dock lines...recheck your exhaust for any steam and your oil breather for steam or water condensation...if all is good you are a lucky man...Go sailing with caution for a while one eye glued to the temp guage and your Tow boat policy paid up..check your engine fluids regularly for the first few days of use...if all is well change oil and take a sigh of relief you lucked out.

It may use a little more oil and be harder starting then it use to with a tint of blue smoke out the exhaust..if so you scored the cylinder walls a little and have lost some compression..aging the engine by 2500 hours or so...BUMMER!...not the end of the world so still count your self lucky.

"Go Simple...Go Large"

Relationships are everything to me..everything else in life are just tools to enhance them.

The purchase price of a boat is just the admittance fee to the dance...you still have to spend money on the girl...so court one with something going for her with pleasing and desirable character traits others desire as well... or you could find yourself in a disillusioned relationship contemplating an expensive divorce.

Last edited by Stillraining; 02-20-2010 at 11:27 PM.
Stillraining is offline  
post #3 of 10 Old 02-21-2010
Senior Member
MARC2012's Avatar
Join Date: Mar 2008
Posts: 594
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 13
Can not add to previous follow sr advice.marc
MARC2012 is offline  
post #4 of 10 Old 02-21-2010
Telstar 28
sailingdog's Avatar
Join Date: Mar 2006
Location: New England
Posts: 43,289
Thanks: 0
Thanked 20 Times in 15 Posts
Rep Power: 19
Before starting the engine, it would probably be worthwhile to change the oil and check the condition of the oil. Water intrusion into the engine will often leave the oil looking "milky".


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

sailingdog is offline  
post #5 of 10 Old 02-21-2010
Senior Member
Join Date: Oct 2009
Location: Gloucester, MA
Posts: 586
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 11
The advice above is very good. I just wanted to add some encouragement before you tear into this that engines like the md7a are actually pretty tough so don't despair until you actually find a problem. I have worked on a lot of overheated engines and it is shocking to me how often we can't find any problems and it runs just like it did beforehand.
klem is offline  
post #6 of 10 Old 02-21-2010 Thread Starter
Senior Member
FishFinder's Avatar
Join Date: Feb 2008
Posts: 139
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 13
OK great tips thanks, we will see how it goes. Will suck if I have major issues but right now I'm just happy there wasn't a fire and I was able to make it back to my home dock easily.

1980 S2 9.2A (30') in Anacortes, WA
Aux power 13hp Volvo MD7A
FishFinder is offline  
post #7 of 10 Old 02-23-2010
Senior Member
Stu Jackson's Avatar
Join Date: Jul 2001
Posts: 1,167
Thanks: 0
Thanked 32 Times in 31 Posts
Rep Power: 19
Originally Posted by klem View Post
....don't despair until you actually find a problem.
I agree.

And to borrow kelm's idea:

I have overheated my engine altogether too many times, and it is shocking to me how often we can't find any problems and it runs just like it did beforehand.

If you catch it right away, that helps. So many things can happen: intake debris, we lost our coolant from a hidden hose breaking to the hot water heater under the galley sole, the old I forgot to open the thru hull (only once in 13 years, so far!), the old M25 alternator bracket broke, you name it, we've had overheats.

Engine is still smilin' back at me!

Stu Jackson, Catalina 34, 1986, M25 engine, Rocna 10 (22#), Maple Bay, BC, Canada
Stu Jackson is offline  
post #8 of 10 Old 03-03-2010
Junior Member
waynemk's Avatar
Join Date: Dec 2007
Posts: 13
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
I would also look at the exhaust side. Hotter than normal gases exited the heat exchanger it could do damage to any plastic or rubber components. i.e. exhaust tubing and muffler.
waynemk is offline  
post #9 of 10 Old 03-03-2010
Still learning!
Join Date: Feb 2010
Location: Hampton, VA
Posts: 7
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0

Stillraining gave a lot of good information and advice but I thought I'd add just a bit here. Had a 2GMF Yanmar on my old Hunter 31 that overheated a few times and here is what I learned:
1. DO NOT IMMEDIATELY SHUT DOWN THE ENGINE UNLESS YOU REALLY HEAR SOME BAD (GRINDING) NOISES. Remember, when all internal combustion engines are shut down, the core temperature actually RISES (known as "heat soakback)! Why? Think of why you really start to sweat when you first get off a bike or complete a run. What little cooling you may have had is now gone. What you should do is reduce power to idle and wait a minute or two, then shut it down. That will allow the block to cool naturally and dramatically reduce heat soakback. You can do even more damage to the engine by immediately shutting down an overheated engine!
2. Start at the intake seacock and work your way all the way through the engine to the water lift muffler to determine the reason for the overheating. If there is a problem in the SW cooling side, you will see a drop in water flow out the exhaust. The primary culprits are: debris in the intake, clogged SW filter, bad impeller, clogged heat exchanger and a clogged mixing elbow. I'd take my time and work my way one step at a time. I had a situation once when I'd changed the intake hose on the "vaccum" SW side from the filter to SW pump. Used the wrong kind of hose and every time I ran the engine higher than 1500 rpm, the hose collapsed and the engine overheated. When I shut it down to check the problem, couldn't find anything wrong! Had a mechanic take a look and he figured it out in about 5 seconds. Best $50 I ever spent on that boat!
3. If SW flow is not a problem, it has to be in the FW side and unless you are using too "strong" an antifreeze mixture it is almost certain to be either the thermostat or clogging in the FW side of the heat exchanger.

If you saw smoke in the engine compartment, that isn't a good sign but could be the heat burning off engine paint or something else like that. I would definitely change the oil (and it wouldn't hurt to save a sample and have it analyzed. Matter of fact, that is probably one of the best things you can do since you will get all sorts of valuable info on the condition of you engine) and make sure the oil isn't milky or smells burned. I'd also make sure you don't have any leaking seals (head gasket, etc.) which could have been compromised in a severe overheating.

Good luck.

Tim L.
S/V "Magic" C400
Chesapeake Bay

Last edited by Magic1; 03-03-2010 at 06:39 PM. Reason: gave wrong boat name in narrative. Added info.
Magic1 is offline  
post #10 of 10 Old 03-04-2010
Senior Member
Omatako's Avatar
Join Date: Sep 2003
Location: Auckland New Zealand
Posts: 2,705
Thanks: 1
Thanked 36 Times in 33 Posts
Rep Power: 17
If there were no agressive noises just before the engine was shut down, the chances are it'll be OK. If an overheat is going to do any damage, it'll start with pick-up between the rings and the barrels and that makes noise.

Most engines that die from overheating generally don't do any damage to the bottom end (crank and bearings). If there were no agressive sounds before you shut down the next worst enemy is water in the barrels from a blown head gasket or similar- the barrels will corrode irrepairably within a dy or two if not stripped and cleaned.

Good luck.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


"Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying."

Arthur C. Clarke
Omatako is offline  

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Forum Replies Last Post
Badly overheated Volvo MD6A...now no compression??? Sur la Mer Diesel 7 08-26-2015 12:44 AM
m25 Overheated SSBN506 Diesel 5 06-08-2013 04:17 PM
Overheated my Yanmar 20gm20f RobGallagher Gear & Maintenance 9 07-15-2012 10:15 PM
What to look for, look out for in a used sail MITBeta Gear & Maintenance 4 06-23-2012 08:36 PM
Palmer P60 overheated rlmccb Gear & Maintenance 6 03-11-2012 10:50 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome