Mercruiser 4.3L v6 TKS Thunderbolt IV

[mercruiser43]

Hello all. I am new to the forum and have already had a lot of my questions answered by reading through other threads on here. All of you are extremely knowledgeable. I myself am a "new to me" boat owner. I have been on many boats in my life however just recently bought a "new to me" boat with a 1998 Mercruiser 4.3L V6 Alpha One TKS Thunderbolt IV engine.

I purchased the boat in May of this year (2013) and have had it out on the water numerous times all summer. She runs excellent up until the last time I had it out (a week ago).

The issue is that when we got past the no wake zone (takes about 5 minutes to idle speed from my dock) my boat would not get up on plane. I had to ask the two passengers in the back to move to the front. This did make the boat plane off however I had had 4 more (and even larger) people in the boat before and have never had to ask anyone to ever move to the front (immediately again verified no water in the bilge... as I did this also before leaving the dock as part of my starting procedure)

Another symptom was that when I was able to get it on plane (after shifting the weight)... and when I trimmed up slightly the boat would sound like it was "winding out" and I would actually seem to "slow down". I was moving along at roughly 1/2 - 3/4 of my normal speed at WOT. I honestly was not paying attention to my tach gauge during this as my tach gauge has not been working correctly since the second time I had the boat out in the water. The needle "jumps" and moves randomly. I think I have moisture in the gauge but I plan to have this fixed during the off-season.

The motor starts right up and there are no obvious sounds of any issues. I have not water tested it since I did the things below however I did put it on muffs 2 days ago and it started and sounded good.

1. Replaced all spark plugs.
2. Replaced spark plug wires.
3. Replaced fuel/water filter.
4. Replaced cap and rotor.
5. Checked all fluids and found the engine oil was a quart low. I filled up the oil with the correct oil it is using 25w40.

Also, the more I read on here the more my problem sounded like a possible spun hub. This would almost make sense to me because while I was in shallow water (about a week before I noticed this issue) my prop picked up a blanket that someone threw (or accidentally dropped) into the water. As soon as I noticed my boat having issues I stopped the engine and trimmed up the prop to have a look. I was able to get the blanket off of the prop without any issues and once it was removed all was fine again.

With that said I took the prop off the other day to inspect the hub. The teeth on the hub look to be in very excellent condition as well as the shaft. What I did notice (and this could or could not be the entire issue) was that the prop nut was extremely loose when I took it off. I read on here I should have at least 55 pounds of torque however I may have been able to spin it off with my hand. I am not sure though, that this would cause the issue of losing power or not though.

The engine on this boat is extremely clean. It was dealer maintained its whole life.

I do keep the boat at a dock and from sitting in the water for 2 months it was extremely dirty when I pulled it out. I also spent the time and cleaned the whole hull and engine/prop area. I used a mixture of lysol toilet bowl cleaner and hydrogen peroxide/water mix. I couldn't believe how well that worked. The FedEx guy stopped by yesterday and asked me if the boat has been in the water yet this year (that's how you know your boat is clean).

Any ideas on what could cause the power loss issues? I know the boat is also currently low on fuel however I have it on the trailer right now covered until I get back from training with my Army National Guard unit at the end of August and will fill it up with fuel than.

This issue is important to me because I do not want to get stuck out on the water, ever.

Thanks to all!

Jason

 

[Watermann]

Re: Mercruiser 4.3L v6 TKS Thunderbolt IV

Sure could be a spun hub, don't you have a spare prop on board? If not now's a good time to get one then and swap them out to see if your right about it being spun. I can see a wet blanket causing all kinds of problems, definitely could de-laminate the rubber hub from the prop housing. It could even cause a lack of water flow into the outdrive. Plastic grocery sacks are the worst, they fly out of peoples boats and the next guy comes along and it wraps around the lower unit blocking the water intakes.

 

[mercruiser43]

Re: Mercruiser 4.3L v6 TKS Thunderbolt IV

Waterman,

Thanks for the reply! I do not yet have a spare prop on board. I realize that is not smart boating but that will solve issues down the road and not the issue at hand. Also, at first I thought it had everything to do with the blanket however I have used the boat circa 10 times (between blanket and having issues). Also, when I hit the blanket I was at idle speed and shut down the engine within seconds after it happened. Also, reading through the forum there are a few ways to check for a spun hub:

1. Visual. The hub/prop looks to be in excellent condition. I would expect a spun hub would have obvious wear signs however this one does not, in fact, it almost looks brand new.
2. Using the marker trick to mark the hub and prop. Run the boat in the water and then check the lines (not yet done).
3. I also read that you can manually turn the prop to check its resistance. I have done this and it is not easy to spin the prop (with the boat out of the water).

I am thinking it has to do with possibly something with the fuel. I filled the boat up at the beginning of the season and haven't used much gas (I live on a small private lake). Most of my time spent is tied off and swimming with friends/family. I have only added about 10 gallons and that was in early June. The boat right now has little less than a quarter of a tank.

I don't know what it could be at this point for sure (and if it is even still a problem now that I replaced so many things).

My only idea is:

1. Something with the fuel or fuel system.

EDIT: More of a reason to think it is something with the fuel (and it being so low) is because the fuel cap on the boat does not seat very tight. It is on the back of the boat and it appears the "tab" that locks it into place has broken off. My theory is, and bare with me, that when I am out boating and coming off of plane that some water/rain can seep into the fuel system. Now that the fuel is low, any water or moisture that got in there is causing the issue, i.e. power reduction, etc.

Thoughts?

 

[Another retired guy]

Re: Mercruiser 4.3L v6 TKS Thunderbolt IV

If the prop checks out ok, have a look at the "sticky" at the top of this forum, specifically #14 - which details many possible causes of low rpm at WOT.

 

[mercruiser43]

Re: Mercruiser 4.3L v6 TKS Thunderbolt IV

Interesting. #1 is accordance with the fuel and goes along with my theory.

I won't be able to test this until late august however I will fuel up the boat with premium fuel and then give it a water test.

Also, I had a gross amount of marine growth on the hull (which has since been cleaned). This wasn't the issue but it wasn't helping either.

Thanks to everyone, looking forward to getting home (leave next week). If I remember too I will try to post my results of the testing once I am done.

(P.S. The reason I can't test it yet is because when I was working on it I attempted to twist off one of the water release valves and it broke... old valve.) I have two coming from ******** (they are back-ordered) so I have to wait for that anyway and dig out the broken part that is still in there.

 

[Bondo]

Re: Mercruiser 4.3L v6 TKS Thunderbolt IV

Interesting. #1 is accordance with the fuel and goes along with my theory.

I won't be able to test this until late august however I will fuel up the boat with premium fuel and then give it a water test.

Also, I had a gross amount of marine growth on the hull (which has since been cleaned). This wasn't the issue but it wasn't helping either.

Thanks to everyone, looking forward to getting home (leave next week). If I remember too I will try to post my results of the testing once I am done.

(P.S. The reason I can't test it yet is because when I was working on it I attempted to twist off one of the water release valves and it broke... old valve.) I have two coming from ******** (they are back-ordered) so I have to wait for that anyway and dig out the broken part that is still in there.

Ayuh,... Welcome Aboard,.... Have ya tried the boat, Since ya cleaned it,..??

That'll effect it Waayyy more than you think,...

Is yer way to open water Weedy,..??
Do ya throw the drive into reverse, 'n gun it when ya reach clear open water, to clear the weeds,..??

Prop hubs usually Go, when they go,.. do the line test, but I'm havin' doubts on that 1,..

 

[mercruiser43]

Re: Mercruiser 4.3L v6 TKS Thunderbolt IV

All,

Just wanted to give everyone an update. I filled up the boat today with premium gas (over $100.00 worth... About 25 gallons) and test drove it today in the water. SHE HAS NEVER RUN BETTER!!!! I am sure some of it has to do with the tune-up (and hull cleaning) but I am convinced that the primary issue (sluggish/doggish/would not plane) was that how low on gasoline the boat was and some water mixed into the tank contaminating the fuel.

Thanks to all for your help and suggestions.

Happy boating!!