anybody experience with Merc 7.4mpi

G

greenstreak

New Member
Nov 1, 2008
86
I got a question. I had a mechanic to put the wrong gasket on the riser/elbow on my 2000 mercrusier 7.4 engine. He put the restictor gasket on and not the open gasket. So 2 openings on each riser was closed off. It made my engine run hotter at first but now it will over heat as sson as I get on cruise. I found out after 4 months he had installed the wrong gasket. Could this have hurt my engine? Could it have blown a piece in the head gasket? Maybe leaking gases into the water jackets? I know that will make an engine run hot when at higher speeds.

Thanks

art
 
If you kept running the engine while it was overheated, then yes, there might be damage. If you immediately shut it down and let it cool then you probably are OK. If you are really worried you can have a compression check done and borescope the cylinders. If you have closed cooling you can also have the cooling system pressure checked.

The compression test will help identify any head or head gasket issues. The borescope will identify any cylinder scuffing by overheated (too much expansion) pistons. The cooling system pressure test also tests the integrity of the head gasket. Might be worth doing if you can do those jobs yourself or at little cost. I wouldn't lay out big money to do them unless you strongly suspect a problem or you ran the engine while it was too hot.

Best regards,
Frank
 
Hey Frank---I have been running the boat since this mechanic put wrong gaskets on. I thought the dash gauge was going bad. The temp would get up around 200 on the gauge but alarm never went off. But the last three times out the alarm would go off. I check the engine with the ir gun I bought and at the risers it was 207 and at thermostat housing 208. But I shut down as soon as the alarms went off and let it cool. The engine seems to run fine except for overheating now. I just don't know what effect it had on the engine cause the 2 openings were closed on each riser.

Thanks

art
 
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I think this would be the correct gasket for your engine...
5805.jpg




But this is the one you got...
5829.jpg


I'm confused - I was under the impression that all MPIs were FWC, but I guess I was wrong. If you were FWC, you'd have something like this...

5804.jpg
 
frank--Yes I should have the 4 slotted gasket the mechanic installed the one with 2 small holes in it. that is called a restrictor gasket. It is used when the hose is also coming off the riser. My hose only comes from bottom of manifolds. Yeah there is fwc and rwc 7.4

thanks
art
 
rondds said:
I'm confused - I was under the impression that all MPIs were FWC, but I guess I was wrong.
Click to expand...

Ron - I actually have not seen alot of FWC 7.4 mpi's in single powered 270's. The newer 8.1 appear to all be FWC. Mine is also rwc - I ended up installing a fresh water flushing system - but I sure wish I had the FWC.

Your pic's are accurate.

Green - FWIW - I will add to Frank's note and say once you pull the plugs out, often the plugs that have a head gasket leak (water entering cylinders) will usually look super clean (steam cleaned).
If I were a betting man, I would think you have no damage.

Mark
 
The 7.4 MPI's are Half FWC, meaning the block is FWC and the manifolds are raw water cooled. The 4 port riser gaskets are the ones to use, no restrictions.
More than likely, the exhaust shutters are now burnt out because of the lack of cooling water. The bits will restrict exhaust gas flow down in the "Y" pipe and cause a drop in power and cause overheating.

Get your Mercruiser manual here http://forums.iboats.com/showthread.php?t=251571

Find Service Manual #23, RIGHT click on the link and "save target as" this will download the manual as a .pdf file.
 
hey chris---I check the exhaust flappers yesterday and they are still good. No problem with them.

thanks
art
 
If you reached only 200 degrees F on those risers, it's doubtful you did any damage. You could get those engines much much hotter than that before damage would occur. Usually the first thing to go is the head gasket which may or may not require the heads to be decked and reinstalled. It doesn't sound like you've reached that point.

Doug
 
I doubt you did any damage. Overheating is 250F or above.

Best regards,
Frank
 
could raw water intake in the outdrive get clogged up? I have checked everything like impeller, all the coolers and the exhaust flappers and everything is ok, but I am still getting hot at cruise. Is that the only water intake for the mercruiser 7.4/bravo III? how do I find out if it is clogged in the outdrive?

thanks

art
 
Art
Isn't the problem the gasket? If the gasket was correct, I'd imagine you'd be back to running around 170 degrees and you wouldn't need to look elsewhere for the source of the problem. If the wrong gasket is installed and the mechanic knows it, why wouldn't he replace it with the correct one??
 
hey Ron---I changed the gasket. Took it out and still runs hot on cruise. That is why I am wondering did the wrong gasket blocking water flow has caused any damage to my engine?

thanks

art
 
The Bravo III has the raw water pump mounted on the engine. Have you checked the impeller? When was the last time it was replaced? Is the pump housing scored?

Doug
 
hey Ron---I changed the gasket. Took it out and still runs hot on cruise. That is why I am wondering did the wrong gasket blocking water flow has caused any damage to my engine?
Ok, sorry. I missed that one.

I have never heard of the intake clogging but I suppose there could be growth in there. The only intake is through the drive. Could be a busted vane from the impeller lodged somewhere down the system, but you said you checked the impeller already. What about a bad temp sender? Did you shoot any laser temp readings to confirm with the gauge is telling you? Are the risers touchable during cruise (ie: not scalding hot)?
Click to expand...
Click to expand...
 
Hey Ron---I know it is overheating because I have shot the engine with the ir gun. My alarm has gone off 2 times. I checked the risers at that point and they were 207 degrees. I back flushed all the coolers and hoses today. I did not see anything come out, but after doing this there is a lot more water coming out of the exhaust at the drive. It is pouing out like from a hose. It didn't do this before. I also rechecked the impeller today and it is ok. I won't know if this works or not until I can put the boat in the water and get it up on cruise.

Thanks

art
 
That almost sounds like a clog in the hoses or risers if nothing came out immediately but did shortly thereafter.

Doug
 
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
 
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