Mercruiser 4.3L - No Oil Pressure after Oil Change

Boat: 2006/2007 Bayliner 217SD with 190HP 4.3L Mercruiser V6
Task: Change oil and filter
Problem: No oil pressure after draining oil, replacing oil filter, adding new oil and running the engine

Long story: I've changed oil in my personal cars for over 30 years. I've had cars from Lexus to Mazda to Honda to Saab. All of these cars had oil filters attached to the engine. My 2006 Bayliner 217 deckboat has the Mercruiser V6 with a remote mounted oil filter. While this factory design looks like a good idea for easy access to the filter, it makes for a mess when you change it. But that's another story.

I recently acquired this well-maintained boat and decided to do a thorough cleaning and service. I decided to pull my boat out of the lake store it on my property for the winter. I had several projects that I figured was more practical to perform if I just do the work on the trailer and do the service work on my property instead of on the lift on the lake. One of the simple tasks was to perform an oil change. I purchased Mercruiser/Quicksilver 25w-40 oil and a Quicksilver oil filter from Walmart and was expecting a rather routine operation. I ran the engine for about 5 minutes to heat up the oil, so that draining the old oil would be faster (warm oil flows faster than cold oil). I turned off the engine and got ready to capture the old oil. I then pulled the oil drain tube out of the drain plug and proceeded to empty the oil out of the engine. I collected roughly 4 quarts of oil in about 15 minutes.

I always change the oil filter when i change the fluid. I knew there would be a little bit of a mess here, so I had several towels and rags available when i started to unscrew the remote mounted oil filter, which is mounted upside down. After unscrewing the filter, which was on tighter than I've ever seen a filter, oil spilled out around it. I'd estimate around 1/4 quart was still in the filter and poured out around it.

As luck would have it, a rain storm came and put the project on hold. I put the new filter on to just keep dust form getting in the lines, but didn't add any oil. I postponed finishing the project for another week. When I returned the following week, i expected a simple series of steps would be needed to finish. I put the new oil filter on, 1/2 turn after making contact with the mount. I filled the engine with 4 quarts of motor oil and checked the dipstick to make sure the oil level was correct. Done, right?

I thought it would be good to run the engine for a few minutes to make sure the level was still correct after the oil circulates in the filter and throughout the engine. I put the engine muffs on and turned on the water hose to supply water to the Inboard/Outboard motor. After cranking the engine, the engine started as normal. After about 10-15 seconds, a loud blaring alarm horn sounded. I immediately looked at all the gauges. The oil pressure looked very low. I assumed it was the oil pressure and turned off the motor. I went back to the motor and looked for loose wires, hoses, and anything that might look out of normal. I also checked the oil level again using the dipstick. Everything looked good. I wanted to see if oil was circulating, so i removed the oil filter. It was bone dry. Also, i found that the oil filter was on so tight that I had to use a wrench to remove. I installed the filter again, tried to run the engine again and had hoped the problem was just an anomaly. Same result. the alarm sounded, no oil pressure, and i quickly turned it off. I'm totally confused...

How does a simple oil change result in an inoperable boat? I spent the next several hours looking online for things like: Mercruiser 4.3 no oil pressure after oil change, remote mounted oil Mercruiser oil pressure, oil change pressure loss remote mount, etc. The few results that came up indicated a faulty oil filter, improper viscosity of oil, bad oil pump, and faulty oil pressure sending sensor/gauge. I eliminated a few of those ideas. The oil gauge was working when I drained the oil, the oil pump was working when i heated the old oil, and the viscosity should not be that big of a deal. I went out a got another filter, thinking that could be the problem, but that didn't solve the problem. I finally figured that there might be an air lock between the oil pump and the oil filter. On my Mercruiser motor, the oil pump is located about 2 feet away from the elevated oil filter. See the diagram above.

The solution: I decided to drain about 1/2 quart of oil out of the oil pan and use a small funnel to add this oil back to the engine through the tube that feeds oil to the oil filter. I slowly poured most of that 1/2 quart of oil into the threaded line (shown as #2 on the diagram). After it stopped filling, i removed the funnel and quickly screwed the oil filter back on hand tight. The water was turned on to feed the motor with clean fresh water and i proceeded to start the engine. Within 2 seconds, the oil pressure jumped up to normal. I let the engine run for 7-8 minutes, keeping a close eye on the oil pressure gauge. It held constant. I shut off the engine, let it sit for about 1 minute and then started it again. The oil pressure was just as before, perfect. I turned off the engine, checked the dipstick again and celebrated the success.

Closing Remarks: If you have a remote mounted oil filter on your boat, it's good practice to fill the supply line with oil after you replace the oil. Running an engine without oil/pressure is very damaging to the motor. I'm thankful this trick worked for me and hope you also find it useful. Now, back to boating!