Mercury 230 bogs after about 30 minutes, works fine after cool down.

[JackBronson]

Hello,

I have a Mercruiser MCM 230, 230HP 5 liter, engine serial number B530375, drive unit serial number 0B539283, Alpha 1 on a 19' Starcraft. The issue I am having is that after about 30 minutes of boating the engine will lose power and stall. I have been able to get the motor started and was able to drive it a short distance at a very low speed, keeping the RPMs at about 1000. If I try to power up beyond that, when it gets to around 1500 is bogs out and dies.

The boat had two fuel filters. The filter in the carb (it is a Rochester Quadrajet) I removed as it was filthy. There is an inline glass fuel filter that I disassembled (it is a Spectre brand from AutoZone), cleaned and replaced the cartridge.

It seems an awful lot like a vapor lock situation, as it only happens after the engine is warm. However, the previous owner put a Sunpro temp gauge on the boat and its never gone above 160 (and the first time this happened was in the ocean and it was at about 140) so it's not like the engine is getting overly hot. I am wondering if it is the engine compartment that is getting too warm, and contributing, although that would seem unlikely. It is warm in there when I open the compartment, but it doesn't seem like an oven.

After the motor cools down for a half hour or more it runs fine again. Can pull the kids on the tube for a while and then it happens.

There ARE times I check the glass fuel filter and it seems like it is empty, but I don't know if it is always supposed to have fuel in it. I just can't recall if the times I've seen it empty are the times I've been having the problem. The boat has a full tank of fresh fuel, and I also threw two cans of Sea Foam in it, which may explain all the crap in the fuel filters I replaced.

Any suggestions for why to try next would be greatly appreciated. Thank you.

 

[Eric 3.7LX Alpha 1]

Re: Mercury 230 bogs after about 30 minutes, works fine after cool down.

The glass fuel filter is not coast guard approved for inside an engine compartment. I had one and it broke on me... leaking all over. The internal threads that tighten both halves together either stripped or boke and it came apart. Although very nice to see the filter, I recommend removing it.

Most have a fuel/water separator inline between the tank and fuel pump, and the filter at the carb inlet only.

If your fuel tank vent is plugged, the tank will create a vacuum after running a while and symptoms are like you are describing. You can remove the fuel tank cap when it happens and see if the issue improves, or verify the vent hose and cap on the outer hull of the boat is clear.

The coil may be acting up as well, there is a test procedure in the manual for the coil, by testing resistance between the primary and secondary terminals. Check the manual for the test.

 

[JackBronson]

Re: Mercury 230 bogs after about 30 minutes, works fine after cool down.

Did some investigating and discovered the previous owner replaced the fuel line from the tank to the separator. He must have gotten a deal on the hose because it's about 2' longer than it needs to be. The excess line was laying on the floor of the boat routed underneath the front portion of the motor. I'm going to shorten the line to the minimum it needs to be and attach it to the engine compartment frame so it is not floating around free.

I also found Mercury Service Bulletin 99-7 at http://www.boatfix.com/merc/Bullet/99/99_07.pdf which talks about what seems to be my boat's exact problem. The Starcraft 191s has a very tight engine compartment, and it does seem quite hot when I open the cover. So, I will take some steps to improve that, including running the blower more often and maybe adding a second blower to increase the airflow.

I don't believe the fuel vent line is clogged, as fuel came out of it when I topped off the tank before hitting the lake last weekend.

 

[Eric 3.7LX Alpha 1]

Re: Mercury 230 bogs after about 30 minutes, works fine after cool down.

Just as a side note... they sell a whistle that you install on the tank vent as close a possible to the tank.

http://www.greenmarineproducts.com/fuel-whistle/

When the fuel hits the whistle, the sounds stops and the tank is full. I have one and haven't had any spillage since.

 

[JackBronson]

Re: Mercury 230 bogs after about 30 minutes, works fine after cool down.

Good call, I'll check it out. Especially since 30 minutes before the fuel spill I had spent hours buffing and waxing the hull (DOH!). Thanks.

 

[JackBronson]

Re: Mercury 230 bogs after about 30 minutes, works fine after cool down.

To close this out, my apparent vapor lock issue seems to have been resolved. I took 16" off the fuel tank to engine hose and fastened it with a plastic clamp to a spot in the engine compartment so it is away from the motor. The hose HAD been long enough to lay on the boat floor partially under the motor. I also added a slightly longer hose from the fuel pump to the carb so that the hose is away from the top of the motor as much as possible.

As an aside I also discovered that the air intake/exhaust chrome grilles on the side of the boat were on "backwards", in that the side that the blower attaches to was set up for air in, and the other side was set up for exhaust. as these grilles are directional (somewhat), I decided to swap them just in case.

Thanks for your help Eric.