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Author Topic:   Mercury OptiMax: Under-cowling Oil Reservoir Leak
prxmid posted 07-28-2005 08:59 PM ET (US)   Profile for prxmid   Send Email to prxmid  
I have a 1999 OptiMax 150 HP. Just yesterday I noticed oil leaking from the overflow reservoir under the cowling (not the main reservoir). When I pull the black top off, it doesn't seem stripped.

Is this normal and is the remedy to replace the whole oil reservoir?

bsmotril posted 07-28-2005 11:11 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
That is not an overflow tank under the cowl, that is where the motor draws its oil from to mix with fuel. Think of it as a reserve tank should the feed from the main tank fail. I'll bet you dollars for donuts the lid of the tank is cracked. When the motor is tilted up, the cap is leaking. Look carefully around the inside of the cap where the sides meet the top for the crack, it was probably put on too tight. After replacement, you need to bleed the air out of that tank by running the motor with the lid cracked open until it fills completely with oil. BillS
bsmotril posted 07-28-2005 11:15 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Forgot to add that there was also a factory mod to the oil system in mid to late 1999 to checkvalves into the oil lines to keep them from back draining and possibly leaking when the motor is turned off. If that mod is not done, that can also be another source of oil under the cowl. Though they tend to leak with the motor vertical or tilted up and a cracked tank cap only leaks with the motor tilted up. BillS
prxmid posted 07-29-2005 09:15 AM ET (US)     Profile for prxmid  Send Email to prxmid     
Thanks Bill, That's great information. So is tank replacement simply a bolt on or do I need the dealer to do it?
bsmotril posted 07-29-2005 10:02 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Easy Bolt on for a new tank, nothing to it. BillS
prxmid posted 07-30-2005 12:35 PM ET (US)     Profile for prxmid  Send Email to prxmid     
Apppears that the tank cover inner lining that the cap screws into has stripped.
jimh posted 07-31-2005 09:28 AM ET (US)     Profile for jimh  Send Email to jimh     
[Changed TOPIC; was similar.]

Bill--That is great information. You really know those OptiMax engines.

I think the under-cowling reservoir tank is a nice detail. I believe that the oil feed to the injection pump from there is by gravity. As you described, it gives the oil system some reserve capacity in the case of failure of the lift pump to draw oil to the engine from the main reservoir.

I have never heard of any problems with the oil injection system on an OptiMax. Perhaps this arrangement of a second reservoir under the cowling is part of the reason for the strong performance of that system.

Whalerific posted 08-01-2005 03:50 PM ET (US)     Profile for Whalerific  Send Email to Whalerific     
Do you know what a "normal" oil consumption rate is for the OptiMax 135? I don't see anything about it in the manual.
prm1177 posted 08-01-2005 04:25 PM ET (US)     Profile for prm1177  Send Email to prm1177     
Chiming in here - Oil consumption in a direct injected outboard will vary depending on speed and load. I would check my 17 Outrage II with a 135 every 2 tanks (100 gallons) and would generally add 1-1.5 gallons to the holding tank. Bill told me to check the oil tanks on the Conquest he sold me (twin 135s) every 100 miles or so. My estimate is that the burn rate here (base on my usage patterns) is about 2.5 gallons of oil for every 180 gallons of fuel. So that puts my burn rate at around 80:1. Trolling, you'd use less. At cruise (3200-3800 rpm), that seems a reliable figure. I will have more reliable figures when I get my fuel meters installed.
bsmotril posted 08-01-2005 05:34 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
As PRM177 said, it all depends on the way you run the motor. Typically on a 150 mile day with 4 hours running at cruise, and the rest trolling, I would see about 2/3 gallon oil per motor and about 60-80 gallons of fuel. BillS

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