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  1. #1
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    Air compressor 80 PSI air hose HOT to the touch question.

    Year: 2000
    Optimax 200 HP
    SN: 0T075663

    Ok, so I replaced my water pump last weekend in response to my mysterious temporary "overheat" condition discussed in my previous post that occurred after cleaning the compressor strainer. Everything went great. Fired it up on the muffs to test everything. Water PSI at idle was 3.5 PSI on the Smartgauge and telltale was strongest it has been since I have had the boat (less than a year).

    So, all good so far. Had the cowling off while testing on muffs giving the engine a good look and checking for leaks or anything suspicious. While checking checking everything, I happened to touch the hose coming out of the compressor which after looking in my manual appears to be the 80 PSI air hose from the compressor to the fuel real. The darn thing was so hot it almost burned my hand. I gave it a minute or two and grabbed it again and I felt it go from hot to cool. Is this normal??? Been doing some reading and some have state that the compressor supplies "high pressure cool charged" air to the fuel rails. So my thought is that the air hose should not be hot.

    As noted in Savage's signature, I do not particularly suffer from compressor failure fear. LOL. But is always something I am aware of and check as often as possible to check for any warning signs. The engine has approx 400 hours on it. I have also read that the "new" compressor replacement has been "upgraded" with 2 bearings vs the single bearing that the older models have. Does the "new" compressor seem to be having better success than the old style? Would it be a good idea as preventative maintenance to spend the $800 to replace the old compressor now vs $4k later when/ if it goes and requires fuel system cleaning/ possible injectors?

    Thanks for all the help!

  2. Member
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    #2
    Sounds like you may have been grabbing the coolant line for the air compressor. I wouldn't change the compressor unless it was starting to go bad. You can remove the belt to check for any play in the rod bearing and piston.The new compressors fail just like the older ones.



  3. Banned
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    #3
    Quote Originally Posted by Savage View Post
    .The new compressors fail just like the older ones.
    Well THIS is not very encouraging!

  4. ZO6
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    #4
    Quote Originally Posted by Jstep View Post
    Year: 2000
    Optimax 200 HP
    SN: 0T075663

    Ok, so I replaced my water pump last weekend in response to my mysterious temporary "overheat" condition discussed in my previous post that occurred after cleaning the compressor strainer. Everything went great. Fired it up on the muffs to test everything. Water PSI at idle was 3.5 PSI on the Smartgauge and telltale was strongest it has been since I have had the boat (less than a year).

    So, all good so far. Had the cowling off while testing on muffs giving the engine a good look and checking for leaks or anything suspicious. While checking checking everything, I happened to touch the hose coming out of the compressor which after looking in my manual appears to be the 80 PSI air hose from the compressor to the fuel real. The darn thing was so hot it almost burned my hand. I gave it a minute or two and grabbed it again and I felt it go from hot to cool. Is this normal??? Been doing some reading and some have state that the compressor supplies "high pressure cool charged" air to the fuel rails. So my thought is that the air hose should not be hot.

    As noted in Savage's signature, I do not particularly suffer from compressor failure fear. LOL. But is always something I am aware of and check as often as possible to check for any warning signs. The engine has approx 400 hours on it. I have also read that the "new" compressor replacement has been "upgraded" with 2 bearings vs the single bearing that the older models have. Does the "new" compressor seem to be having better success than the old style? Would it be a good idea as preventative maintenance to spend the $800 to replace the old compressor now vs $4k later when/ if it goes and requires fuel system cleaning/ possible injectors?

    Thanks for all the help!
    Dont know anything about upgraded bearings etc. My experience was this...... Sent fuel rails for cleaning. Ended up replacing fuel rails with new and a couple of direct injectors in the process. Also, raised the question if I should replace compressor at this time. My motor had about 550 hrs at the time. No evidence of any problem with the compressor no noise, no play no indication of problems.....nothing. 250 XS never run hard and maintained the best I knew how. Long short, did not replace.
    10 hrs later I replaced the compressor 2 more direct injectors, cleaned the rails, oil filters, Etc. lots of money.

    Wish I had listened to my gut feeling and had replaced the compressor when I bought new rails. I experienced your concern.
    My experience may not be yours.

  5. Member
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    #5
    The compressor output SHOULD be hot. This is basic physics. When you compress a gas, its temp will rise. Feel the difference in temp between your A/C lines on your car air conditioning system. Big line is the suction line going to compressor. Cold. Small line coming out of compressor is HOT. Only change is pressure going from something like 30-40 psig to 200+ psig.
    2008 Bass Cat Pantera Classic
    2014 Mercury Pro XS 200

  6. Member
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    #6
    Quote Originally Posted by OldTimer57 View Post
    The compressor output SHOULD be hot.
    +1
    David Patten
    Automotive and marine technician.

  7. Member
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    #7
    Thanks for all the responses. Good to hear the line is supposed to be hot. Pfhew! It concerned me when I felt the sudden change in the temperature in the line from hot to cool. Changed in an instant while I was holding the line. Would make sense for the coolant line to change quickly ( I assume) with stats opening, etc. But the air line changing temps that fast was not sure.

    I will try to find where I read last night about the "new" compressor having the "upgraded" dual bearing. IIRC they showed a picture and this person felt that the single bearing was the primary cause of the failures as it was not sufficient to support the side tension as well as the new style with 2 bearings (upper & lower).

    So much for everything you read on the internet is correct, eh? LOL

  8. Member
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    #8
    This is a quote from another forum that I was reading last night. Could not sleep and had google syndrome. LOL.

    "Opti owners.
    Periodically grab your compressor pulley and try to wiggle/wobble it. If there is ANY play/wobble in the flywheel, the bearing in the top of the compressor is failing. It may not make any noise at this point. You may also see a little wobble of the pulley with the engine idlling.
    They seem to last longer in cooler climates so take that into consideration of your poll.
    The new compressor has two bearings instead of one in the top cap assembly but I dont think the new top cap assembly is interchangeable with the old compressor. The assembly can be identified by the tag showing it is made in the USA. All the older compressors were made in Mexico.
    Also see my thread on annually cleaning the compressor cooling water strainer [MODERATOR EDIT] in the FAQ Section at the top of this forum.

    Let me know if this is against the forum rules or if I need to add more info on where the info came from. I provided quotes, but not sure about the forum rules on this.
    Last edited by EuropeanAM; 02-17-2017 at 11:47 AM. Reason: Links available here, no need for competing site links.

  9. Member
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    #9
    Ever fooled with an engine with any sort of turbo-charger? One of the immediate performance boosts is an inter-cooler. Just a radiator-like device connected to the turbo output (which is very hot and which is going into the engine along with fuel). There are air-based versions, versions that have their own water system to cool the air going to the intake, etc. Purpose is to get rid of as much of that heat as possible to make the input air charge denser, which improves horsepower. This Merc system is not a super-charger, and I suspect the volume of air being forced into the cylinder is minimal, and that heat gain might help with vaporizing the atomized fuel as well.

    Another example is an air compressor to inflate a tire. The pressure line right out of the compressor gets pretty hot, at only 30 PSI or so. not the 80-100 range merc uses (depends on motor type and direct injector type).
    2008 Bass Cat Pantera Classic
    2014 Mercury Pro XS 200

  10. Member
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    #10
    It could NOT have been the air output hose, if the temperature went from HOT to COLD. Air output hose will be warm and stay warm.



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    #11
    I will take a look this afternoon and verify the hose I was touching. Thanks for all the input!

  12. Member
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    #12
    I agree with Savage now. Did not notice the "hot to cool" comment. I agree, no way it will ever get cool unless he has some sort of stealth NOS system that is injecting into the compressor input. :)
    2008 Bass Cat Pantera Classic
    2014 Mercury Pro XS 200

  13. Member
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    #13
    Verified that I was grabbing the air line. I inspected the compressor while I was in there and all seems perfect. So must have been having a cold flash or hallucination or something. ;) Did not have time to run it on the muffs to see if I could duplicate it. And no, no NOS system. Lol. ;)

    Thanks again everyone. I would still like to find out if the new compressors have been "improved" or not. Will see.

  14. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #14
    As has been stated, the air output line may become hot to the touch. Perfectly normal.

    I have seen no significant difference in the durability of any particular version of the compressor, regardless of version.

    I would not recommend replacing a compressor unless it exhibits signs of excessive wear, or failure.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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