Mercury Oil Remote Tank Caps

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
brock71
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Mercury Oil Remote Tank Caps

Postby brock71 » Sun Oct 15, 2017 10:51 am

I have a 2004 Mercury 200-HP V6 [two-stroke-power-cycle] outboard engine with carburetors and oil mixing. I have a low oil alarm. It seems to be a leak in the remote oil tank caps. I am constantly fiddling with the caps to get them tight. I replaced the O-ring on each cap. I have used a large oil filter wrench to tighten the caps. Works for an outing. Next time I get the alarm again. I have to crank them tighter.
Am considering replacement of the entire tank assembly.

How tight do these caps [on the Mercury oil remote tank] normally need to be?

A local dealer told me hand tight. No way is that enough on this boat.

Does this engine have the plastic oil pump gear? If so maybe I go pre-mix instead of fooling around with the tank.

Thanks for you thoughts,
John

jimh
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Re: Mercury Oil Remote Tank Caps

Postby jimh » Sun Oct 15, 2017 12:54 pm

As you probably know, the Mercury oil mixing system relies on the remote oil tank to be completely sealed off from the atmospheric pressure so that the tank can be pressurized by that second hose line on the cap. If the caps do not seal completely air-tight, then the tank cannot be effectively pressurized, and oil will not be moved from the tank into the intermediate oil reservoir under the engine cowling.

The oil in the under-cowling tank feeds into the mixing pump by gravity, and the LOW OIL sensor is part of that tank. So the aural alert you are getting is probably because the under-cowling tank level has fallen below threshold, causing the alert.

As for how to remedy the air leak in the remote tank, perhaps there is another point of leaking besides the caps. There was a recent thread here discussing how a seam in the plastic molded tank developed a leak. I recommend a very careful visual inspection of the remote oil tank, looking for any sign of a leak in the upper part of the tank itself. (If there were a leak in the lower part of the tank, you'd probably have already discovered it due to the leaking oil.)

Since many of the Mercury engines from this era have been converted to use pre-mixed gasoline-oil fuel, there must be some used oil tanks around. Replacement of the tank is probably the fasted route to a remedy. Also check the hose carrying the pressurized air. And also look at the check valve on the power head where the crankcase air pulses are taken off to create the pressure.

There is an excellent article available that reproduced the service manual for the oil mixing system on these older Mercury outboards, see

Mercury Automatic Oil-Gasoline Mixing System
http://continuouswave.com/whaler/refere ... ction.html

jimh
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Re: Mercury Oil Remote Tank Caps

Postby jimh » Sun Oct 15, 2017 1:10 pm

Regarding a c.2004 Mercury 200-HP V6 two-stroke-power-cycle engine and the gear drive for the oil mixing pump:

an article in the extensive archives of the website has excellent first-hand information from a Mercury engine mechanic with over thirty-years of experience (user name SOSMERC). He says that in the latest models of these older engines that Mercury made some changes to the system, removing the MOTION SENSOR, and replacing the mechanical pump with an electrical pump. But I don't find any mention of an upgrade to the mechanical pump to replace the plastic gear. As I recall, even the repair parts used to repair a failed plastic gear used another plastic gear.

According to my local Mercury dealer, who've been selling and servicing Mercury outboards for over 50 years, no owner has ever undertaken the expense of repairing a failed plastic gear, and they just moved to using pre-mixed oil-gasoline fuels.

If the plastic gear in your 2004 engine has not failed already after 13-years of service, it is probably good for a few more years. I think the usual cause of failure was just extremely prolonged very high speed operation.

ALSO IMPORTANT TO NOTE:

In the article I cite above, our reliable source of information about these engines, SOSMERC, comments directly on your problem:

...the oil tank caps tend to leak from being over-tightened.


This seems to suggest that the real cause of the problem was likely due to the caps being over-tightened in the first place. Perhaps a new set of caps will fix the problem, assuming the tank openings themselves have not been deformed.

brock71
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Re: Mercury Oil Remote Tank Caps

Postby brock71 » Sun Oct 15, 2017 2:06 pm

Thanks for replying. I wonder if the tank or caps are permanently damaged by the over tightening or not. I'll try loosening them. Should these be just hand tight?

I found a replacement part for the simple tank fill cap, but not for the cap with hoses connected to it.
I have found complete new tank replacements including caps and hoses for about $200.

From the sounds of it the plastic gear will eventually fail. Not too encouraging. I've owned the boat for two years. Not sure how many hours are on it or how hard it may have been run in its life. I guess I'll bet on the gear lasting and go ahead with a new tank.

John

jimh
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Re: Mercury Oil Remote Tank Caps

Postby jimh » Mon Oct 16, 2017 9:43 am

brock71 wrote:From the sounds of it the plastic gear will eventually fail. Not too encouraging.


I don't have any data on the rate of failure of the plastic gear in older Mercury outboard engines with oil mixing. For a while there was an aftermarket solution available from a former Mercury engineer. He designed an entirely new oil mixing pump using an electrically operated pump. I believe this re-fit kit sold for about $600, but I don't think it is still available.

On the basis that there was an after-market solution for this problem, I would infer that there must have been a large number of failures of the plastic gear. It would not make sense for someone to invent a new pump and begin to manufacture and sell a repair kit, unless there was anticipation of a large market for the product.

If you visit another article in the archives you will find more information. Here is an except, a comment I wrote in that article, again a discussion of the failure of the plastic gear:

    Because of the high cost of repair of a failure of the plastic drive gear in the Mercury oil mixing system, an alternative after-market solution has been developed. It replaces the OEM oil mixing pump with an electrically operated pump.
    The cost of a gear replacement is estimated at $1,200. The cost of retrofitting an electrically operated pump is estimated at $575.

    For more information on this solution, see:

    Marine Solutions (Wisconsin)
    http://www.marinesolutionswi.com/

    They have retrofit kits available for Mercury V6 outboards:

    --135 to 200-HP, 1989 through 1999

    --200 to 225-HP, 1995 through 2001 3-liter

    The manufacturer of this retrofit comes with some credentials. Robert Kachelek, president of Marine Solutions, was formerly the director of Outboard Service for Mercury Marine.

--
Please note that the website no longer exists and the linked site is an archive of the original site that was available in 2007.

What is interesting is the date range for the re-fit kit. It seems to end at 2001. Perhaps that is indicative that Mercury changed something in their engine production around c.2002. That Mercury began to use a different pump is also mentioned by SOSMERC. Perhaps the epoch for the change to a different design was c.2002, and perhaps your engine has the newer, electric pump design. A look under the cowling should reveal the answer.

jimh
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Re: Mercury Oil Remote Tank Caps

Postby jimh » Mon Oct 16, 2017 9:52 am

Also take some solace in this comment, again in regard to the caps for the Mercury remote oil tank:

The cracked cap for the under cowl reservoir is probably the most common failure point for the Mercury Oil System across the mid-to-high-power two-stroke and DFI product line. Join the club, a lot of us have also already been there too.--BillS


So there you have another first-hand account of failure of the caps on the Mercury remote oil tank. It is also from the article in the archives I linked above.

brock71
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Re: Mercury Oil Remote Tank Caps

Postby brock71 » Mon Jul 27, 2020 2:10 pm

I thought I fixed my problem with the remote tank not pushing oil up to the engine mounted tank. The problem was intermittent. Tried o=rings in the tank caps. New cap for the engine mounted tank. Finally put in a new check valve. Seemed fixed. Now with less than 20 hrs of operation I again have the problem. Thinking of replacing the hoses. Are these 3/8" ?

Is there anything in the oil delivery cap on the remote tank that could fail?

How much pressure should be developed in the remote tank?

Any idea what would cause a crankcase check valve to fail?

Thanks for any input.
John

floater
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Re: Mercury Oil Remote Tank Caps

Postby floater » Mon Jul 27, 2020 3:59 pm

On my 1991 Mercury 200 two stroke my large on boat oil tank swelled up like a balloon one time. Turns out the check valve on the motor had failed and wouldn't allow the main oil tank to depressurize. I too tighten my oil tank caps with a large oil filter wrench. The tightened oil tank caps do seem to be able to hold allot of pressure. Have you replaced the two large oil tank caps themselves? There may be a small crack in one or both caps. I went to a marina and they had a used tank they sold me for 20 dollars with no caps. You may be able to find another used tank to try if you don't want to buy a brand new one.

brock71
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Re: Mercury Oil Remote Tank Caps

Postby brock71 » Tue Jul 28, 2020 9:20 am

I have not yet replaced the remote tank caps themselves. Just cleaned them and put new o-rings in them. I see no evidence of any oil leaks. Tomorrow I am going to attack it again. My plan is to pressurize the hose from the engine crankcase check valve from a small compressor with a gauge and regulator to 5 or 6-PSI. Then sEe if oil transfers up to the engine mounted tank.

If the oil is pushed to the under-cowling tank, then the check valve is probably bad again.

If the oil does not transfer then I have an air leak or blockage to track down.

John

jimh
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Re: Mercury Oil Remote Tank Caps

Postby jimh » Tue Jul 28, 2020 11:37 am

I think there is a check valve in the system that might regulate the tank pressure to only 2-PSI.

brock71
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Re: Mercury Oil Remote Tank Caps

Postby brock71 » Tue Jul 28, 2020 12:07 pm

I am curious about the possibility of a pressure regulating check valve. I see one in the crankcase to supply pressure and one up near the engine mounted tank set to 2psi to allow air into the tank if oil flow from the remote tank stops. IS eiter one of these the pressure regulator function?
Thanks
John

brock71
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Re: Mercury Oil Remote Tank Caps

Postby brock71 » Wed Jul 29, 2020 3:01 pm

Went after the oil transfer concern again. Applied 5lbs pressure to the hose connected to the crankcase check valve. Plenty of oil transferred from the remote tank to the engine tank.

Blowing through and sucking on the check valve verified it acts like a check valve at least to some degree.
Measured the pressure supplied by the crankcase check valve. I get 2.5lbs pressure from the crankcase at idle. At higher RPM it drops to 2 lbs. IS this normal?

I have not been able to find a specification for how much pressure is normal. Anyone know?

Next checked engine compression. All 6 cylinders were 134 to 140 [bs. Within normal range.

Did find something interesting in the hoses that run from the remote tank to the engine. Both have been spliced. An inline hose barb in each hose near where they enter the engine cowling. One barb connection on the oil hose did not have a tywrap clamp. It was just pushed on. MArks indicate it had a clamp at one time. So I added a clamp. Could air enter here? I would think oil would leak out if there were a loose connection here.

Bottom line.....its working again. For how long I don't know. What did I do to make it work? Blew air through the check valve, pressurized the remote tank to 5lbs, and tilted the motor up and down a number of times. VooDoo next?

Appreciate any thought you may have ....especially on normal remote tank pressure.

John