3gmf oil blow out through dip stick; Hunter 34

D

Damspacher

.
Feb 1, 2004
12
Hunter 38 BYC, Middle River
I recently arrived at an anchorage to find that I had lost about 2 qts of oil, apparently through the dip stick. I believe the oil leaked through the dipstick because oil sprayed out through the ventilation hole on the starboard side of the engine compartment. When I checked the dip stick it was in the tube. Is there a valve or something other that could create enough pressure to lift the dipstick if it were not functioning properly or clogged?
I have ran the engine since and only have small amounts of oil dripping off the engine which I believe is residual oil falling off the engine from the "big leak".
Any help would be appreciated.
What a mess, lots of oil flowed thru the engine compartment weep holes into the area between hull and inner liner.
Regards,
Dave A
 
Jake N Eggs

Jake N Eggs

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Jun 2, 2011
347
Hunter H33 Port Credit Harbour, ON.
The crankcase should have a breather to expel internal pressure. Sometimes the breather is vented into the intake so the gasses are burned in the engine. Because the dipstick tube goes int the bottom of the oil pan it is below the oil level it is possible to have oil pressed out of the dipstick tube if the crankcase pressure rises if the dipstick is not sealed well.

Excess pressure can be developed in the crankcase by compression gasses bypassing the piston rings, clogged crankcase vent, or over filled oil and the oil being aerated by the connecting rods. Once the oil is aerated it could pump a lot of oil out before it settles down. It is also easier to press aerated oil out of the dipstick tube.
 
Charles Erwin

Charles Erwin

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Jan 30, 2012
1,147
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Before condemning rings and such check/clean the crankcase vent tube. It goes from the rocker cover to the air intake. The vent tube needs to be clear and so does the trap which is screwed into the the rocker cover. If not you get exactly the symptoms you describe. By the way always verify the dip stick is fully seated in the hole. If not then oil loss will happen there too

Charles
 
kloudie1

kloudie1

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Nov 6, 2006
10,113
Hunter 34 Mandeville Louisiana
No dipstick tube on 3 GMF, so unlikely that much oil could be forced out of dipstick. Dipstick goes into a hole in the block and there is a 4" or so open space to the oil surface. Do check the reed valves in the breather. They are in the box on aft end of valve cover. Check breather tube as well as Charles says.
Wipe it all down and clean with detergent then start the hunt. Good luck
 
Last edited:
HMT2

HMT2

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Mar 20, 2014
900
Hunter 31 828 Shoreacres, TX
Dave I had a similar problem with my Yanmar 2gm. I found the dipstick in its hole but unseated and oil everywhere...twice. Bought a new dipstick and that solved the problem, the new one fit much tighter.
 
G

geek_guy

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Dec 29, 2012
148
Hunter 37 Jacksonville
I second HMT2. I had the same issue and a new dipstick fixed mine as well. My mechanic said he's seen several like that. Who'd have guessed.
 
D

Damspacher

.
Feb 1, 2004
12
Hunter 38 BYC, Middle River
Thanks for the input guys. This weekend I will disassemble and clean the breather and I will order a new dip stick. Claude....you are correct there is no tube on the 3gmf.
 
R

Rick486

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Oct 1, 2007
1,865
Boston Whaler Super Sport Pt. Judith
I had this happen once and it turned out to be the oil pressure sender. It had failed and exposed 45 psi to an open hole. Worth a look.
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
geek_guy said:
.... I had the same issue and a new dipstick fixed mine as well. My mechanic said he's seen several like that. Who'd have guessed.
Click to expand
Maybe it was a seal in the cap of the dipstick? I can't imagine the stick itself being a problem.
 
HMT2

HMT2

.
Mar 20, 2014
900
Hunter 31 828 Shoreacres, TX
Ron20324 said:
Maybe it was a seal in the cap of the dipstick? I can't imagine the stick itself being a problem.
Click to expand
You are correct there is piece of rubber around the dipstick top, on my old dipstick it had hardened over the years. Once I put the new one in my problem was solved.
 
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Likes: kloudie1
D

Damspacher

.
Feb 1, 2004
12
Hunter 38 BYC, Middle River
The breather was clear. We took the boat out today and it happened again only difference was I was keeping an eye on it thus avoiding the mess I had the first time. If the new dip stick doesn't fix the issue I am wondering if it could it be a faulty oil pressure control valve? On the 3gmf its part of the assembly that you screw the oil filter on to. If pressure exceeds 43 to 57 Psi it opens and expels oil into the timing gear case. Not sure how much it takes to lift the dip stick. Rick mentioned the oil pressure sender. Doesn't this part only set off an alarm at the panel when the oil pressure is too low?
 
M

Morgan donor

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Sep 17, 2012
110
Morgan 383 Fairhaven, NY
No. not likely as the crankcase isn't pressurized under normal circumstances (unless the breather is blocked).
I don't know if a yamar will do this but some older perkins will: If there is a bad diaphragm in the mechanical fuel pump, it will pass fuel into the crankcase. Overfilling the crankcase, perhaps exiting the dipstick and other bad things can happen. Looked for thinned oil and smell of fuel on the dipstick, as well as abnormally high oil level.
 
F

Fast Ed

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Jun 27, 2004
113
Hunter 34 New Bern, NC
The dipstick is next to the fuel pump on a 3GM30F. I would be looking at the pump.
 
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