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Thread: coolant smell

  1. #1

    Default coolant smell

    Hi again,

    I have twin Crusader 8.1L 2004 with full closed cooling system in my boat. Two winters ago we completely replaced manifolds, risers, raw water pumps and hoses; cleaned HX and oil coolers, and replaced belts and belt tensioners. Over this past winter I found some coolant in the bilge on the outboard side of my port motor. The mechanics at the yard took a look and said there was an overtightened hose clamp and they pressure tested the entire system and it's fine. So far this season I have not seen any coolant leaking in that same place so I guess it was fixed. I have put 60 hours on the motors this season no problems.

    This leads me to yesterday - I checked the oil before yesterday's trip and notice the overflow tank on the port motor was all the way full (way above the "full" mark). I ran the boat out 10 miles and fished for a few hours and when I returned to the harbor and came to idle I noticed a burning smell from the helm. At first I thought it smelt like wires burning, but then I felt it was the smell of burning coolant. The engine temp gauges read within 5 degrees of each other and the port motor was the cooler one just under 180 degrees F, stbd was just over 180. I got back to dock and raised the hatch and find the overflow tank on the port motor still full to the top and there is some coolant on the outside of the tank bottom where the return line goes back to HX, and there were little spots of coolant sprayed in the bilge and on tranny just below that spot.

    This morning I drained the overflow tank back down to the "full" mark and fired up the engines and let them warm up. The port motor warms faster than stbd on the gauge, but the gauge never reads above 180. I used infra heat gun all over the motors. What I found is that the risers on the port motor are ~10 degrees or so warmer than stbd, and the inboard manifold of the port motor is reading 200 degrees in some places in the center just under the riser, while the other three manifolds I can never find much over 180 degrees. After heat up and cool down the overflow tanks on both engines stayed exactly in same spot. If I take off the HX caps when cool they are not full, you have too look down inside to see the coolant. Is that expected

    I am kind of at a loss here for what to do next. Any advice appreciated.

  2. #2
    Join Date
    Dec 2011
    Location
    San Jose del Cabo, MX, Osprey, FL
    Posts
    311

    Default Re: coolant smell

    Well, "something" forced an excessive amount of coolant out into the overflow bottle and just as importantly, from a diagnostic standpoint, for some reason the coolant was not sucked back into the system when it cooled. Two possibilities immediately come to mind. First, the cap could have somehow failed or was not on tight. The system was running unpressurized and you got some localized boiling on a hotter spot on the cylinder walls and the steam pressure forced out some coolant before it was swept away. The system being unpressurized did not suck the coolant back when the steam bubble collapsed or when the engine cooled.

    Or second, you have a small head gasket failure that is allowing combustion gas to enter the coolant system and force coolant out into the overflow bottle. When the engine cools, the head gasket leak allows air to enter the coolant system so it does not develop enough suction to pull the coolant in the bottle back in.

    You could swap caps to test one scenario, and test for combustion gas in the cooling system (or pressure test the system) for the other possibility. There may be other suggestions made that you should also consider.

    I would go after this one pretty quickly as a head gasket problem could worsen and leak the other way (coolant into the cylinder) and create some significant damage.

  3. #3

    Default Re: coolant smell

    Quote Originally Posted by CaboJohn View Post
    Well, "something" forced an excessive amount of coolant out into the overflow bottle and just as importantly, from a diagnostic standpoint, for some reason the coolant was not sucked back into the system when it cooled. Two possibilities immediately come to mind. First, the cap could have somehow failed or was not on tight. The system was running unpressurized and you got some localized boiling on a hotter spot on the cylinder walls and the steam pressure forced out some coolant before it was swept away. The system being unpressurized did not suck the coolant back when the steam bubble collapsed or when the engine cooled.

    Or second, you have a small head gasket failure that is allowing combustion gas to enter the coolant system and force coolant out into the overflow bottle. When the engine cools, the head gasket leak allows air to enter the coolant system so it does not develop enough suction to pull the coolant in the bottle back in.

    You could swap caps to test one scenario, and test for combustion gas in the cooling system (or pressure test the system) for the other possibility. There may be other suggestions made that you should also consider.

    I would go after this one pretty quickly as a head gasket problem could worsen and leak the other way (coolant into the cylinder) and create some significant damage.
    Thanks for the reply. I don't know how to test for combustion gasses in the coolant. I tried to find pH strips but no one carries them around here. They all carry the bubble tester. I guess I'll try that.

    When I replaced all the cooling system parts I replaced the caps too. I noticed the cap on the port side has some pink on top right in the center, as if some coolant came out there too. I think I still have the original caps that I can try.

    Should the HX be full of coolant when cool?


    Is there anything you can think of that could create that smell in the engine compartment except for coolant on the outside of the engine somewhere? I just don't know where the smell is coming from. The overflow tank is on the back of the engine over the transmission. How hot does it need to get to create that smell...?

  4. #4

    Default Re: coolant smell

    Alright so I have an update: I am at the boat early this morning attempt to burp the cooling system on the smelly engine. I take the cap off HX and pour in a good amount of coolant and indeed a lot of air comes out. Fill it up more and more air comes out. So air is definitely in somewhere. I think this is the first time this was done since the pressure checks this spring so the air bubble may have been there entire time. I warm up the engine with cap off of HX and overflow tank. First thing I notice is coolant flowing in HX and then it starts to fill as pressure builds. I quickly replace cap on HX and leave cap off overflow tank. I did notice a bit of coolant dripping from HX cap so maybe the neck is bent or cap not providing a great deal. I also notice a bit of steam coming from the overflow tank after things come up to temp. Hopefully that is not exhaust from engine. I need to find hydrocarbon test strips somewhere and test coolant.

    BUT! The smell came back almost immediately upon starting the engine. No way it was soon enough to be burning residual coolant on outside of engine. I think the smell is coming from front Of engine and not rear where the spray was. I think maybe my original intuition about it being smell of hot wires instead of coolant and start checking temps with the infra gun. I find the alternator on the port engine is 215-230 degrees in spots. I compared to alternator on stbd motor which is at 130 at most. I think that is the culprit of the smell.

  5. #5
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,824

    Default Re: coolant smell

    i'd bet you have made progress....at least on one of the issues

  6. #6

    Default Re: coolant smell

    Pulled the alternator and took it to the shop. They say it has a short and is only pushing 10 amps. Rebuild in progress. I'll get it back tomorrow and reinstall.

  7. #7
    Join Date
    Dec 2011
    Location
    San Jose del Cabo, MX, Osprey, FL
    Posts
    311

    Default Re: coolant smell

    OK, you likely have cured the smell by fixing the alternator. Now as for the coolant....In a properly filled and operating system there is no air whatsoever in it. And a system with too much air in it will do strange things. The idea is to fill it as full as possible. Try squeezing the hoses to burp the thing. If your engine requires a thermostat with a small hole in it, and you do not have that then it will be very difficult to get the air out. After filling as much as possible idle the engine with the cap off and add more coolant if the level goes down (air bubble comes around). Once you have done your best, you close it up, fill the overflow bottle half full and bring the engine to temperature. The system is designed to expel the remaining air as the warming fluid expands. This only happens upon warm up. When the engine cools it should suck back fluid from the overflow bottle to replace the air that was expelled. You may then need to add fluid to the overflow bottle to bring it to half full. You need to go though 2-3 heat/cool cycles to get all of the air out. Note that the air is only forced out on warm up so a 30 minute run works as well as several hours. It is heat/cool cycles you need.

    When properly operating the fluid level in the overflow will rise several inches upon warm up and fall back to the original level when it cools. If this does not happen you have a problem. If the tank bubbles when underway you have a problem. If the overflow tank fills up and overflows you have a problem.

    If none of that happens enjoy your ride!

  8. #8

    Default Re: coolant smell

    Unfortunately I have another update. I had the overheating alternator rebuilt by an alternator shop. Bolted it up and tested output and it was perfect and the smell was gone. Ran for a couple of hours alone as well. On the return trip I noticed the engine running rough at idle and knocking. Given that the alternator was the last thing touched I check the voltage output and it's bad at 12.45v. Thinking and checking everything else, long story short the rebuilt alternator had an internal wire come loose (not sure but I think it's one of the diode wires) and the connecting part that looks like some kind of brown epoxy part was loose inside the bottom of the housing.

    In was In rough water when running so wasn't as easy to tell that the engine was misfiring when running at 3k RPM.

    Is there anything else I should look out for that might have been damaged from running the engine this way?

  9. #9

    Default Re: coolant smell

    Well... I pulled the rebuilt alternator and took it back to the shop. Indeed the diode was the problem. They repaired it and I bolted it all back up and now she puts out 14.2v. However, I still have the engine rattling / knocking at idle. It seems to go away completely if I put it in gear or bump the rpms up by even 100 from idle.

    I guess it could be completely unrelated to the alternator issue and just have developed at the same time by coincidence. What are the obvious things I should be checking for the knocking / rattling in neutral at idle only?

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