Compression Test

[Switchback]

Ahoy everyone!

So, I've got a potential head gasket issue. I need to perform a compression test. I've searched the forum but I have been unable to locate a step-by-step. Has anyone had experience completing this diagnostic and willing to provide me with some detailed steps on doing this? I'm having a hard time figuring out what adpaters/threads to use and what compression test kit to buy. Just feeling a bit uncomfortable doing this myself and can't get a mechanic to come out.

Some more info about the issue:
Universal M25
White smoke in exhaust (definitely not steam)
Coolant loss (no visible leaks)
Oil level normal (no gunk on oil cap)
No water in diesel

Any help would be super appreciated! Thanks! :)

[Ron Hill]

Switch : While others will give you the details on a compression check let me give you one tip!!  Make darn sure that you turn OFF the raw water thru hull when you do that check!!!

A thought

[Switchback]

Switch : While others will give you the details on a compression check let me give you one tip!!  Make darn sure that you turn OFF the raw water thru hull when you do that check!!!

A thought

Good call out, that could be disastrous!

[waughoo]

On a diesel, I have always had it done through the glow plug socket.  As for threads etc, I would suggest pulling one and head to the plumbing shop and see what you can make up.  Most easily available compression test kits will be for the spark plug socket.

[Switchback]

On a diesel, I have always had it done through the glow plug socket.  As for threads etc, I would suggest pulling one and head to the plumbing shop and see what you can make up.  Most easily available compression test kits will be for the spark plug socket.

I just ordered a kit which I believe comes with the correct glow plug adapter. Fingers crossed! Seems much easier than having to pull each injector.

[KWKloeber]

@Ron

OK, I'll bite, why close the thru-hull - what's different than just attaching a gauge?  Are you meaning flooding the muffler/hydrolock? 
Another option is (IMO better) to open the muffler drain (which coincidently forces maintenance/replacing it if it needs that.) Plus it keeps the impeller lubricated.

@SB

Let's do some troubleshooting before jumping to the conclusion that it may be a head gasket.

What makes you say that -- does she run any differently "now" than "before"?

Year of the engine?
Any maintenance on it, such as
   * changing the Hx, or is it original? (2"? or 3"?)
   * changing or disturbing the exhaust flange or gasket on the exhaust manifold?

Are you losing a quart a day or a cup a month? Perspective.
What are the sea conditions?  temp/humidity when you notice that?  Possibly high humidity and low sea temp?

If you have a cylinder that isn't exploding correctly due to compression or the injector you can sequentially crack open the fuel line to each cylinder (interrupting the fuel flow) -- (use protection to keep diesel from blowing all over.)  When a "bad" cylinder is hit the change in RPM, rough running, will not be as great as when other "normal" cylinders are not firing.   

If she's losing coolant and there's a cloud following her -- then WHAT IS the cloud if it's not coolant (i.e., steam??)  is there a coolant odor?

Pressure test the Hx if it is "old," you could be losing coolant thru there - more likely than a blown head gasket.  Occam's Razor!!!  You can do that on-engine with a simple pressure gauge or get a simple/CHEAP Horror Fright brake line vacuum tester -- it's worth its weight in Rubles when troubleshooting water and fuel line leaks.

[Switchback]

What makes you say that -- does she run any differently "now" than "before"?

The engine has only run four times this season.

First was about 5 minutes, moving the boat from my winter slip to my summer slip - no issues there.

The second was a sail to an island (engine ran for maybe 1hr total) - no issues.

Third time was another sail to a mooring - this is where I noticed the white smoke, I chalked it up to condensation due to temp difference between water and air. Engine ran for maybe 45 min.

Fourth time sailed to another mooring - white smoke again in exhaust and was thicker than previously. Engine was on for another hour.

I noticed the engine temp was about 5 degrees higher than normal - checked coolant and I lost about half an inch of fluid. Oil was fine, no signs of water in diesel, no signs of exterior coolant leakage.

I am seriously hesitant to run the engine without further diagnostic. If the head gasket IS blown and coolant is diluting the oil that is bad news for the pistons and cylinders or so I have read

Year of the engine?

Engine is original to my 1986 c34

Any maintenance on it, such as
   * changing the Hx, or is it original? (2"? or 3"?)
   * changing or disturbing the exhaust flange or gasket on the exhaust manifold? - I did recently remove and replace the entire exhaust riser including flange and gasket. First attempt I did not get a proper seal on the pipe threads going into the flange. I removed again and properly sealed/tightened all pipe connections and changed out the gasket for a new one. My thought was that if I did not properly seat the flange gasket that the coolant could be leaking directly into the exhaust riser from the back of the manifold. I checked with a diesel mechanic and they said this would not be possible. (I still think this is a possibility however I spent a long time ensuring that the surfaces that the gasket mates to were spotless)

Are you losing a quart a day or a cup a month? Perspective.
What are the sea conditions?  temp/humidity when you notice that?  Possibly high humidity and low sea temp?

It was early season when I noticed the white smoke, and truth be told I did notice other boats with white smoke coming from the exhaust at that time, but due to the issue occurring on separate occasions and the white smoke increasing in thickness I kind of ruled this out as being steam from condensation.

If you have a cylinder that isn't exploding correctly due to compression or the injector you can sequentially crack open the fuel line to each cylinder (interrupting the fuel flow) -- (use protection to keep diesel from blowing all over.)  When a "bad" cylinder is hit the change in RPM, rough running, will not be as great as when other "normal" cylinders are not firing.   

If she's losing coolant and there's a cloud following her -- then WHAT IS the cloud if it's not coolant (i.e., steam??)  is there a coolant odor?

I was unable to detect an odor as the smoke was trailing behind and not wafting into the cockpit

Pressure test the Hx if it is "old," you could be losing coolant thru there - more likely than a blown head gasket.  Occam's Razor!!!  You can do that on-engine with a simple pressure gauge or get a simple/CHEAP Horror Fright brake line vacuum tester -- it's worth its weight in Rubles when troubleshooting water and fuel line leaks.

I purchased a compression test kit on Amazon for quite cheap that supposedly comes with the correct glow plug adapter. I will probably start here. If compression is normal then I think the next logical step is HX or a leak into exhaust riser

[Ron Hill]

Ken : You are right again IF you want to screw around with that muffler drain.  Personally I DON'T and would recommend that others do not either, because people (other than you) tend to forget!!!   I use the Globe impellers that are "Run Dry" !!

A few thoughts

[KWKloeber]

If the closed WATER system is leaking then what you test/isolate is the closed WATER system, not the cylinder.
The M25 has (at least) 3 potential causes of losing coolant out the exhaust, so why focus on the least likely one?

The FiRST logical step is a vacuum test on the seawater side of the Hx (easier than a pressure test, and easier than on the coolant side.) 

The SECOND logical step is to test the exhaust manifold, first just as it sits (connected to the engine block.)  Using a radiator pressure tester (loaner from auto parts) OR the same brake line vac pump as on the Hx.
Test #2 fails THEN test w/ the EM isolated (block off the two hose paths to the engine.)

If #1 Hx test fails, it's a bad Hx.
If the EM test #2 fails, it's either an exhaust gasket leak or a water jacket leak.
If the EM test #3 fails, it's the gasket. If EM#3 test passes, it's a water jacket leak.

If you have no coolant in the oil (you will see the muddy concoction on the dipstick) you don't have a head gasket problem.  There's no evidence to suggest that -- head gaskets don't just "go bad."  You didn't overheat (warp the head,) bla bla bla. 

You likely have either:

     a) A leak at the exhaust gasket.  If you install it backwards, 100% of the coolant will be in the sea within 5 minutes.  A leaky one will dribble coolant into the exhaust. 
Find a new "mechanic" if one tells you anything otherwise.

     b) A pinhole leak in one tube in the Hx.

Because you did exhaust work, evidence suggests that is the cause. 
Except what is "recently"??? 
Just before the incident?  Had the engine run ok for one season after doing the work?
Was she run ok one time?
Complete info helps us to help you.

You didn't answer is it the 2" or 3" Hx? 


I WOULD NOT be surprised if she came up 5 degrees SOLELY because of a 2" Hx.    That needs replacing sooner than later anyway - at 36 years you are WAY overdue and on not borrowed time, but defibrillator time.  Even if it is the 3".  However, losing coolant as well - says to me you have a bad Hx right NOW, not soon.   
Typical Hx life is maybe 20 years -- my 2" Hx pinholed at 15 years (freshwater.  Salt is worse, obviously.)

If time is of the essence you're wasting time chasing a less than 1% chance of the cause. 
Or go with your gut, YBYC.

My assessment after 29 years owning and working on others' M-25s is:
   Under normal circumstances - 90+% chance it's your Hx;
   However, because of the prior work it's 50% chance the gasket.
   0.1% chance it's a head gasket. 

Did you replace or test the pressure cap?
Is there coolant being pushed into the overflow reservoir? (and not returning?)

If continued use/reliability is critical -
(1) Replace the Hx -- it is going to fail soon if it hasn't already.
(2) Put a wrench on and tighten the exhaust flange nuts.

YBYC how you decide to proceed. 

[KWKloeber]

I use the Globe impellers that are "Run Dry" !!

I'd like to try those but have heard (from Depco) that they don't pump as much volume.

[Ron Hill]

Ken : Come ON.  If an impeller has the same number of vanes and fits into the same cavity - I would surly believe that at the same RPM it would pump the same amount of water!!

A few thoughts

[KWKloeber]

One would think so but I believe your comments should be taken up w/ Depco/George Cornelius, not the guy quoting him.
Depco is <tongue in cheek> always "the expert" and authority, eh?

One consideration I could think of is that, being aftermarket, possibly Depco had issues w/ them not being quite as tightly to spec as genuine Sw and Ob impellers?  Maybe the material causes excessive wear?   I dunno,  I didn't ask George why - I uncharacteristically simply took his recommendation at face value.

[Ron Hill]

Ken : Have no idea why it would pump less water??, but I'm VERY happy with Globe impellers in both the Ob and Sh pumps !!  I've used them since about 1990 and have NEVER had a old Globe impeller loose a blade!!!!  Also don't know of anyone else that lost ever a Globe blade!!!!

A thought

[Switchback]

Good news! I have checked my compression and each cylinder looks good! So happy to rule out a head gasket issue. I think my next step is going to be inspecting the heat exchanger for pin holes.

[Ron Hill]

Switch : You might want to also look at all of your hose connections and the end caps of the heat exchanger.

A thought