Black Coolant

[rardiH36]

Hi all:About six months ago I purchased an 1980 Hunter 36 with a 2QM Yanmar engine. It is fitted has a heat exchanger, so an anti-freeze coolant is what goes through the engine. The boat had been on the hard for six months before my purchase. And probably it was even a long time before that the the coolant had been drained/replaced. Also I found (and had fixed) that the heat exchanger was leaking between the raw water and the coolant interface. The coolant from the engine when I drained it was not salty, so it appears that the coolant was lost to the salt water discharge. The previous owners probably just topped off the engine coolant a lot with fresh water. The color of the coolant when I drained it was very black.Today was the launch. After about an hour of total motoring, I checked the coolant level and noted that the color is still dense black. I expect that I've just got a lot of dirty passage-ways that need flushing out.But can any other more sinister engine conditions cause black coolant?The engine seemed to work just fine. I was able to get up to the rated RPM and nothing unusual in the exhaust.Thanks for any insights about black coolant water.

 

[Capt Ron;-)]

Tom List in Saus

Mr. Rardi, See Tom List in Sausalito 415-332-5478.He's at Schoonmacher Pt just down the hill from the 7/11 on Bridgeway.He is a great guy and the bays expert on Yanmars.I suspect that the pencil zincs need changing in the Ht exchanger and have caused this blackened fluid...Call Tom, he would know.

 

[RichH]

BLACK cooling water usually means ....

blown head gasket. Get a mechanic to put in UV Blacklight fluorescing chemical, run the engine, then have the mechanic come back with his 'black light' device. If the coolant now 'fluoresces' when the black-light is directed into the fill port of the heat exchanger (fresh water side) then you have a blown head gasket. The fluorescing chemical thats added fluoresces when the water is highly saturated with CO2 (product of combustion). First off drain the whole system, flush thoroughly and replace with fresh clean water, if it again turns BLACK-ish then have the above test performed. Such a head gasket leak goes in 'two directions' the cylinder compression pushes soot into the cooling water on the upstroke and sucks water into the cylinder on the down stroke. Alternatively, if you have a 'radiator cap tester' ... put it on the fill cap (fresh water side) of the heat exchanger and pump it up to 15 psi. If it leaks down in pressure after a few minutes (and the freshwater loop is not leaking out externally) .... blown head gasket,Its hard to diagnose from a far distance; but sorry, Ill give you 10:1 odds of a blown head gasket on this one.

 

[rardiH36]

Black Head And Gasket

Dear RichH:Not sure about an enthusiastic thank you for the news that its probably blown head gasket ... but the analysis is very appreciated and is taken on board. I think that I would have headed down the "get a mechanic path" if the coolant turned black after a couple of drain/flushes. Now I will talk to the Yanmar shop (List Marine per Capt Ron's reference) after just one more drain/refill.Do you think I am risking much extra damage to the engine if it is run for a few more hours?OK, I'll say it... Thanks.regards,Richard

 

[Steve Dion]

Check out some other sources for engines too!

Richard:Be sure to check out some other sources for engines repairs/replacements. I would contact Barbara at Golden State Diesel too. KKMI is also a Yanmar dealer too.One of the dealers in the bay replaced one of these QM engines in my friends HC37 and I think the price was up around $15-17k. That included shaft seal, prop, strut replacment and several other items.

 

[Doug]

I wouldn't dispair just yet

A while ago there was black antifreeze, I think it was factory GM's eco stuff not sure, but it's possible that's all it is. I'd put the green stuff in and cross my fingers before I spent alot of money.  To quick test for a head gasket watch the fluid in the coolant tank and rev the motor hard. Not high rpm's but quick acceleration, if it's blown, air bubbles will blow through like it's on high boil for a second or two. Natuarly the fluid will jump and flow but it shouldn't have big air pockets. Best of luck

 

[Landsend]

sometimes you can smell an exhaust smell in the...

black coolant and this will confirm a blown head gasket. Also it will really raise the pressure in the coolantsystem.

 

[Capt Ron;-)]

Always Check, not always mate

I just changed a head-gasket in an A-4 (you need TWO) last winter, but we had water in the oil.He may be right, dunno but we did have one that had black/gray stuff that was from the zinc braking up in its final thros.I hate woring on engines, have had to trouble-shoot at sea, but internal engine problems are over my head.Sure, Steve is correct on getting different views/estimates (don't know for sure it IS a head-gasket yet) and Barb in Oakland is VERY knowledgable and kind, but so is Tom and he is close by you. Do NOT go to KKMI in Richmond.Tom is the most honest guy in the marine engine business, not cheap but will steer you in the right direction, and that is even if you do it yourself. He will be in San Diego all next week.Good luck, let us know how it goes for you.Steve, say hi to Ben Parent up there at Delta, great guy...;-)

 

[Fred Ficarra]

Ron, just for your edification

Most Yanmars don't have zincs. That's the case with all of the fresh water cooled ones I know of.Stick around, we'll turn you into an engine guru in no time.Rardi, sure sounds like a blown gasket. But take heart. It's fixable. Just pull the head and check it for warp-age with your machinists' straight edge. I would have it surfaced if you find it more that .002 off. You can check the block too, but it's probably OK.  How many hours on the engine? A valve job is a good idea. Especially when you find all that nasty water in your combustion chamber. That, and a head gasket should be the limit of your expense. I'm guessing a hundred bucks, tops. You do, do your own work don't you?

 

[sand sailor]

head gasket

been working on engines most of my life.it'll leak when cold and stop when warmed up until it goes completely .keep a close eye on coolant levels and get it fixed asap

 

[rardiH36]

Black Coolant - Thanks All Responses

Thanks all for the useful responses about black coolant. I did take a sail yesterday ... my maiden voyage ... from Alameda to my new berth Sausalito. It was a postcar perfect sort of day. Stiff but not excessive wind and crystal clear sky. The engine ran fine for the trip, but I was nervously paying good attention to it. The coolant did not get seem to get any darker, so my first step I think will be to flush the coolant and observe what happens on the next start up. As I wrote on my opening post, the previous coolant (probably without any percent anti-freeze) might have been in the engine for a couple of years with only a few instances of actual engine operation. If there is any indication that the black is returning, then I'll turn my attention to getting an expert to evaluate .... particularly the head gasket.For Fred Ficarra: Yes, I almost always do my own work since I enjoy taking things apart and rebuilding them. Not yet on a marine diesel engine, but in past stages of life I've taken apart an rebuilt a few auto and motorcycle engines. I have lots of mechanics tools and also the official Yanmar engine manual. On my boat, the cockpit sole right over the engine is actually a 2.5' x 3.5' hatchcover. Remove it, and the engine is right there. For cylinder head and exhaust manifold work, it will be almost as good access as if the engine was sitting on a workbench! I am the new owner of "?" many since the boat was built in 1980. I acquired it with what is apparently a new hour guage -- not connected. Again thanks all.

 

[Don12364]

Compression Test?

Doesn't anyone do these any more?

 

[Don S/V ILLusion]

compression test

Donalexany marine diesel mechanic with the proper equipment should be able to do it

 

[Fred Ficarra]

rardi, you're good to go!

If you've assembled car engines, have at it. Theres very little difference. Donalex. I think most of us feel a compression test in this case would not yield meaningful results. Rardi said his engine runs great. The compression would have to be low before it would start to run rough. That's not the case here. But a head gasket-leak will manifest itself in the coolant long before the engine runs rough. (in most cases) The other problem with diesel compression checks is they require specialized testing apparatus. You can't just go down to the local auto parts store and screw it into your spark plug hole. The injector has to come out and the instrument secured in it's place. The pressures are high enough to be a hazard for the non-professional. (like me) Then you have to do the rest of the cylinders for a proper comparison. And because diesel are operated a low speeds compared to gas engines, they rarely have meaningful/significantly low pressure loss in a comparable way. Whew, I don't think I understand what I just wrote.

 

[SeaRanch]

I may be jumping in this a little late, but...I have a H31 2GM Yanmar. Last year I noticed that the coolant was black.Had a mechanic look at it, the pressure test was OK. Then I realized that I had owned the boat for 7 years and had never flushed nor changed the coolant (always just added). I drained, flushed (Prestone Flush), drained again, connected a fresh water hose up to the system and ran water through the system (with the engine running) until clear water running out.Refilled with new coolant, no problems. I have since added the "drain, flush, drain, refill" to a regular maintance schedule. Just maybe you did leave some old coolant in the system.  Bill

 

[NYSail]

Coolant......

When I purchased my boat last year (Yanmar 3HM35F) the radiator did not have an overflow tank. Instead, the hose ran under the engine to a plastic engine guard/pan that after inspecting it had antifreeze, dirt and oil in it. I am assuming that when cooling down the engine would suck this garbage in. Also, my antifreeze was a dark greenish black color. This year I bought an overflow tank from the autoparts store ($15.00 verses $65 Yanmar) and installed it. I also flushed the antifreeze several times without the thermostat until the water ran crystle clear. Reinstalled a new thermostat and put in the "ORANGE" antifreeze as is now recommended by Yanmar. This year, the engine stayed nice and cool, and the antifreeze is a beautiful orange color!Good Luck!Greg

 

[Don12364]

Fred

I,at least, understood what you wrote having worked on engines myself - and I still stick to my opinion that a leaking head gasket will manifest itself in a low pumping pressure. Proprietary gauges come with injector adaptors which overcome the hazards of high pressures. Also the cranking speed with injectors removed will be similar to a petrol engine.I agree the contaminated coolant will show before rough running but so will a low cylinder. Yes it is work but will detect the failure more surely than any of the above quoted remedies. For those to work it needs to be a bad leak which IMHO would probably also cause rough running.Then again a low cylinder pressure might be the result of worn rings or valves. Either way the head must come off.