anybody experience with Merc 7.4mpi

greenstreak said:
hey Doug---What I meant was when I back flushed the hoses and coolers I never saw any pieces of the impeller come out. Water was flowing. After putting all back together I ran the boat using muffs and this time more water was flowing out the back of exhaust then before. Before I did this water only splt out. now it is flowing like coming out of a hose.

thanks

art
Click to expand...

Art,

Thanks for the clarification, but now I'm even more perplexed as to why this would happen unless you disturbed a clog somewhere.

Doug
 
hey doug---I feel the same way. Before I back flushed the amount of water was less coming out. There is nothing in my coolers. All three of them are free of any pieces. If there was a piece of impeller it would have to be in one of the hoses. I will be taking the boat out again tomorrow to see how the temperature is.

thanks

art
 
hey guys---I am afriad I might have major problems. I have checked everything out but I overheat within 5 minutes getting up on cruise. I might have a blown head gasket. I am going to do a test using a clear hose going from the thermostat to the bottom of manifold. If there is bubbles in the water then I will know for sure. Since the mechanic that installed the wrong riser gasket, I believe it might have caused the head gasket to blow.

thanks

art
 
Let's get back to basics....

1. Have you replaced the thermostat?
2. Have you tried running the boat in the water without a thermostat? Does it overheat then?
3. Have you fully removed and inspected the risers on both sides? Have you inspected the manifolds?
4. I tried to reference a diagram for the bravo III but I'm having some difficulties finding the one I'm looking for. What I'm trying to determine is the fresh water pickup in the drive itself, how is that setup? I'm seeing some O-rings of some sort on the diagram, but I can't find the upper side of the drive? Basically what I'm getting at is, if there is a leak in any gasket, Oring, etc on the fresh water tube prior to the pump, you will be sucking air and the pumping ability will degrade possibly causing an overheat condition. I had this exact situation occur previously but on another drive setup. It took me several weeks to diagnose.
5. You said the impeller in the pump was OK, how about the clearances in the pump? Was there any scoring on the pump body or pump plates?

That's about all I can think of right now.

Doug
 
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I have the 7.4 MPI Manuals and Bravo III - manuals - if interested PM and I can send them your way. Make a reasonable offer and they are yours. I had a 2000 - 260 Dancer with your same power package. Good Luck with everything.
 
Hey Doug--I have checked about everything you have mentioned. I did a head gasket test today. I installed clear hoses from thermostat to bottom of manifolds. There are a lot of air bubbles in the water. This indicates a blown head gasket. That is why I overheat in about 5 minutes on cruise. Now I know when the head gasket blew. The second trip out after the mechanic installed the wrong riser gaskets I was on cruise and all of a sudden I bogged down like I was dragging something. At the time I didn't know what had happened. After getting back up on cruise i got about a mile down the river and my overheat alarm came on and I came to idle and it cooled right down. So I idled back to the dock. The engine has been getting hot eversince that happen while I am on cruise. When I tried the boat out before this mechanic messed it up, it ran at 168 degrees all the time we were out testing it. After he did the inspection it ran hotter. I thought the gauge was bad or the heat sending unit. I bought new unit and installed also. I had no way of knowing he installed the restrictor gasket on my boat. All this heat and pressure is what has blown the head gasket. Wow! What a mess over a $4 gasket.

Thanks

art
 
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greenstreak said:
Hey Doug--I have checked about everything you have mentioned. I did a head gasket test today. I installed clear hoses from thermostat to bottom of manifolds. There are a lot of air bubbles in the water. This indicates a blown head gasket. That is why I overheat in about 5 minutes on cruise. Now I know when the head gasket blew. The second trip out after the mechanic installed the wrong riser gaskets I was on cruise and all of a sudden I bogged now like I was dragging something. At the time I didn't know what it was. After getting back up on cruise i got about a mile down the river and my overheat alarm came on and I came to idle and it cooled right down. So I idled back to the dock. The engine has been getting hot eversince that happen.
Click to expand...

So after you installed the clear hose, did you run the engine when you observed these clear bubbles? You may be able to do a leak down on the water jacket side of the engine by plugging various cooling ports and then pressurizing with a pump. When you back flushed with water, did you pull any plugs to see if it's leaking into the combustion chamber? Just trying to think of everything before you go tearing things down.

Doug
 
Hey Ron---You are right about the gaskets in the picture you posted. It was suppose to be the open gasket and not the restrictor. I am sure this stopped a lot of water from passing through the elbows. This had to build up a lot of pressure inside engine with a lot of heat.

Thanks

art
 
Art:
Do you think this mechanic is going to own up to the problem? ie: who picks up the tab for the new head gasket and any other collateral damage?
 
Hey Ron-- There is no way he can deny not doing it. I have the invoice where he states he took off risers and inspected and replaced with new gaskets. As soon as I took off the risers and saw the gasket he put on I took pictures of it. I also have a witness that saw the gasket. I also saved all the pieces of the gaskets. I don't know yet if he will be man enough to take care of the problem or i will have to sue him. I hope it is only the head gasket that blew. Hopefully it didn't warp the heads. I have talked to Parker boats here and they want $2,000 to replace head gaskets. I thought that is very expensive. I will check around next week to see if I can get this done any cheaper. I sure don't want the mechanic that did this to do the work.

Thanks

art
 
Why don't you do it yourself?

If you can pull the risers and such, it should be pretty straight forward to do this as well.

Doug
 
Hey Doug---I wish i could, but I want to make sure it is done right. There is a lot of things that have to come off before taking intake manifold off and then to the heads. I just want someone that is certified with the Mercrusier 7.4 mpi engine. I sure don't want the same problem as I have now with a mechanic that was suppose to be experienced, but put wrong gasket on the risers.

I ask this mechanic how experienced was he on mercruisers before I would let him work on it and he said a lot. I had an oil leak coming down the back of the transom on the inside. I thought it was the hose going to the outdrive reservoir. He said that it was a 5 hr job to get to the barb where the hose was hooked to on the back of outdrive. He said the whole steering assembly had to be taken off to get to it. After he left that day I got a flashlight and checked in back of the engine. He was incorrect. All was in the way was a bigger hose. Just remove that hose and the small hose and barb was in sight. The steering assembly wasn't in the way. So this guy doesn't know much about mercrusiers. He misrepresented himself.

thanks

art
 
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well guys, I gave up and took my boat into the local Sea Ray dealer today. They are going to check it out tomorrow to see what is wrong with it overheating. i will let you know what I find out.

art
 
hey guys---They found the impeller housing bad. It had grooves in it. they said that will let water flow around the blades on the new impeller and engine will overheat. They said the other mechanic should have replaced it when he installed new impeller. Also, they said it was normal for the big block to run around 200 degrees at the elbows while on cruise running at high rpms. They said as long as the water temp is staying between 170 to 190 that was fine. This is what they do all the time is work on mercruisers at the sea ray dealer.

art
 
Agreed abt the housing. It's plastic and crap. For the extra $50 or so in parts (and no more labor than replacing just the impeller), you should replace the housing at the same time. The one impeller I had the marina replace for me, the did just the impeller. When I learned how to do it myself, I bought the entire kit and replaced everything. Not sure what protocol on that is. But is really no more work to put a new housing on since you have to take the pump off and apart to get the old impeller out. When reassembling, you just put back the new impeller in the new housing and bolt it up.
 
hey douglee25---There were grooves in the old plastic housing when the place I took the boat to checked it out. It was at a certified mercruiser place. They said they will not change impeller without changing the plastic housing. they found in the past the water will travel around the blades causing a less of volume of water. They said the mobil mechanic should have changed it. Everything seems ok now.

thanks

art
 
Have been reading your thread after just joining up and know how you feel after having killed a seawater pump while trying to flush my rwc engine.

Great to hear the problem has been solved without busting the wallet.

It may also be worth a look on the water intake side of the oil cooler (under the port riser) as I found several bits of impellor lodged there despite several attempts to flush hoses.
 
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I keep telling you guys that it's nuts to replace just the impeller in those crappy plastic body pumps. You have to replace the body, gaskets, and the impeller. Otherwise there is no point in doing the job. It's just a waste of time and money.

Best regards,
Frank
 
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