8.1 Mercruiser starting to run hot/steam

Discussion in 'General Maintenance/Repair Questions' started by Jimmy Buoy, Jul 30, 2020.

  1. Jimmy Buoy

    Jimmy Buoy Well-Known Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
    Well, I couldn't deny it any longer. My port exhaust has been consistently showing more steam than the stb. My temp gauges consistently show the port engine about 170 degrees while the stb is 155. Using my IR temp gun on the tops of the risers while cruising, both port risers were 175 while the stb engine's risers were both around 150. With my thru hull exhaust ports I can also see a definite reduction in water flow at both idle and 2000rpm with the port engine vs stb.

    I assumed the problem was the fresh water pump. My engine room actually has room and the engines are facing forward with direct shaft drives so it only takes about 1/2hr to remove the pump. Once removed I cracked it open and... the impeller looks relatively new... Not looking like the problem. Took another 1/2 hr to reinstall the pump.

    Next, I looked at the strainer and its hose and didn't see anything out of the ordinary there.

    Next, I vacuumed out hose going from the pump to the engine - nothing.

    Next, I decided to take off the main heat exchanger end caps. Removing the hot side first, I was shocked to see that the rubber gasket between the cap and exchanger end was horribly deformed. It was swollen up and was almost gel like and some of it had broken off and lodged into the hose end heading for base of the stb side exhaust manifold. The "cool" side end cap was similar, but not as badly swollen however some of the rubber had become lodged in a few cooling tubes. They started out as flat disc like gaskets with a hole in the centre.

    IMG_0397.JPG IMG_0396.JPG

    I've cut two new gaskets from sheet gasket material, purchased two O-Rings and plan to reinstall tomorrow and take her for a run to see if this is the cause of my overheating issue. I really wouldn't be surprised after seeing how much the deformed/swollen rubber gasket was intruding to the working room within the exchanger ends and even blocking some core tubes as well as restricting the output hoses. I plan on running a wire thru the cooling tubes before installing the caps though since a few of them have rubber stuck in them.

    I'll update after completing this job. Sidenote - my stb engine had an issue with it's exchanger in 2009 with an internal leak and resulting loss of coolant. I tried unsuccessfully to repair it and ended up buying a new one just under one boat buck so I'm sure it's end cap gaskets are still ok.
     
  2. joeyleggz

    joeyleggz Active Member

    626
    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
    That very well might be the problem . my engines run at 170 all day long ,160 thermostats usually run at 170 for freshwater cool the engines , 145 thermostats are meant for raw water cooled usually run around 150 or so.
     
  3. Jimmy Buoy

    Jimmy Buoy Well-Known Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
    I've owned this boat for 12yrs now and both engines have always run just under 160 with both gauges being virtually the same. It's possible that the gauges are both off, but with such a long track record it's more of an indication that there is a problem when the temps of one engine are constantly up from the other - not normal for my boat. Also, there are all the other symptoms (steam, riser temps).

    The other thing is that the temps on the port engine climb as the engine is put under load unlike the stb engine. That points towards cooling water starvation to some degree and has never been the case with either engine.

    I should know later today!
     
  4. joeyleggz

    joeyleggz Active Member

    626
    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
    Good luck my friend I agree with the track record analog gauges build up resistance over time since I’ve owned my boat for eight years she’s always sat at 170 I gave up on trying to figure out the patterns of steam we have very long exhaust runs and I can tell you that it changes hour to hour and day today depending on the environmental conditions of how much steam I will get out of my exhaust .I’ve already re-powered both motors so I’ve seen the before and after with regards to the steam and nothing really changed . Running into the wind wisps the steam away quickly ,with a tailwind while running it seems to trail 5 to 10 feet behind the boat depending on the day. Climbing temperatures under load definitely indicate a problem
     
  5. Jimmy Buoy

    Jimmy Buoy Well-Known Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
    Update,

    Well, I ran a wire through each accessible tube in the cooler to ensure that no rubber was remaining to block part of the water flow before installing the end caps. I fired her up and was getting a bit nervous as it took longer than normal for water to start flowing out the exhaust, but I did get most of the raw water out of the system so the delay made sense.

    The flow rate is definitely back to being the same as the stb engine and the engine is back to staying under the 160 mark. I'd say "Nailed It" would be in order - yes!

    So for those with 8.1's or 496 (both the same engine - one inboard & the other I/O) that have an issue with water flow you may want to check the cooler end cap gaskets if they're over 15yrs old. It might be the issue and it's much easier to check than pulling the raw water pump. Not sure if other engines would develop similar issues or not since there are so many types of coolers and the 8.1's ares specific for that engine only.
     
    Dabble, M Prod, JustRight and 2 others like this.
  6. Timeflys

    Timeflys Active Member

    260
    Dec 7, 2013
    Thousand Islands, Ontario, Canada
    "Frequent Flyer"
    2002 Sundancer 360
    Merc Horizon 8.1s
    Thanks .... great info..
     
  7. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    304
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1 V-drives
    Yes, great post. Like your analytical approach to the problem. I had the similar issue on my 5.0 in my 2000 290. Same fix.
     
    Dabble likes this.
  8. douglee25

    douglee25 Well-Known Member

    Jan 13, 2008
    Dallas, TX
    Cruisers 3575
    Twin 7.4l
    Do you have a Pic of the HXer assembled?

    My mind escapes me but I could have sworn they didn't have removable end caps?
     
  9. Jimmy Buoy

    Jimmy Buoy Well-Known Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
    Douglee, from your signature it appears that you have 7.4l engines which are quite a different animal from the 8.1S and will probably have a totally different heat exchanger.

    Here's a parts diagram for the 8.1S exchanger...

    https://www.perfprotech.com/mercury...ed-cooling-system/assembly/7460/170?model=323
     
  10. douglee25

    douglee25 Well-Known Member

    Jan 13, 2008
    Dallas, TX
    Cruisers 3575
    Twin 7.4l
    You're correct. They are different than minw, however, I just couldn't place them that they had removable end caps. Thanks for the pics.
     
  11. M Prod

    M Prod Well-Known Member

    Oct 6, 2017
    North Vancouver, BC
    2005 Sundancer 340
    Zodiac Cadet w/FCT console Yamaha F20
    Kohler 5KW Genny
    8.1 Horizons /V Drives
    Thanks Jimmy. This is great info and I’m glad it solved your issue. I’m all over this. My port engine has always run slightly hotter than my starboard since purchasing the boat 3 years ago (170 vs 158 at cruise) and I’ve done pretty much everything under the sun to resolve it ..except switching out heat exchangers or checking this. I’m going to look at this this week.
     
  12. Jimmy Buoy

    Jimmy Buoy Well-Known Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
    Glad to provide another avenue to check out. It's quite easy to take the caps off and take a look. (much easier than swiping heat exchangers!)

    Two years ago I noticed the temps going up throughout the season on that engine, so thinking it was the pump I pulled it and rebuilt it. The impeller didn't look bad at the time. Maybe it had a bit of a "set" but no cracks on the veins. I did see that the pump housing had some decent grooves at both ends of the pump so I even went to the extra step of installing a kit with new stainless wear plates for either end of the new impeller (that was cut shorter by the company to fit properly with the wear plates). At the time it did increase the water flow somewhat which was evident by the slight reduction in engine temps, but I remember being rather unimpressed with the difference. I was convinced that the grooves in the pump were reducing its effectiveness.

    Now it makes sense that the real issue was the ever expanding exchanger rubber gaskets which were blocking more and more of the water flow, and eventually becoming weak enough to break into smaller pieces creating more blockages. I guess that's what can happen to rubber exposed to hot water over almost 20yrs of seasonal usage.

    Let me know how it goes. Your boat is 4yrs newer but you won't know till you take a look!
     

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