Coolant leak cannot be found, HELP....

[lucknow]

Hi all:
My 1989 340 express cruiser has twin 454's with closed coolant systems, it has been repowered and the motors have 300 hours on them. Starting last year, I loose 1/2 gallon of coolant on the port motor after approx 3 hours usage. There does not appear to be any external leak, there is no coolant in the bilge beneath motor, the engine runs fine, no misfires, do not think it is entering the cylinders, the hot water heater is hooked up to that motor, no signs of coolant in the heated water. no signs of leak at the circulation pump on motor, no excessive steam out of exhaust while running, in fact the steam is the same as starboard motor. Now here is the strange part, If i use the boat and then park it for a week. when I return and check the coolant level, the coolant system is still pressurized. The leak does not occur when motors are not running. It lost no coolant over the winter, I swapped heat exchangers from side to side and the leak remains on the port side. I left a pressure tester on the coolant system when cold at 15 lbs and it did not lose pressure after 2 hours. I am thinking it must be leaking from exhaust manifold, but I would think there would be coolant pressure loss after engines are turned off. I am out of things to check, I am considering putting a sealant in that motor to see if it stops the leak. Has anyone got any ideas or suggestions?:smt100

 

[berth control]

sounds like it could be through a manifold, that is what mine was doing under similar circumstances. The steam will be hard to see since it will not really burn until the engine is hot and working hard, and at that time there may be enough exhaust volume to dissipate the steam, or if it's IO's you can't see it while at speed because it exits under water and can condensate back into water before it reaches the surface due to the cold lake water. Mine held pressure also, but when the manifold got warm it would expand and the crack would then leak. If I spend a lot of time at idle or no wake speeds it would never get hot enough to leak. I know manifold's are not cheap, so you could switch them from one motor to the other and see. I guess it's up to you, spend the time and be sure or spend the money and sweat less :grin:

You could be losing some through the water heater, to make sure you aren't I would just take off those hoses and put rubber caps over them, that's what I did to rule it out with my mysterious leak.

 

[fwebster]

If you pressure test the cooling sysemt and leave pressure on it. If the manifolds are leaking, the reason you can't see the antifreeze is because it is going into the mufflers then overboard.

Try removing the large rubber exhaust tubes from the risers the repeat the pressure test. I bet the leak is obvious.

But here is a caution. Usually the manifold fails from the exhaust passage in, not the inside out. The riser usually fails first and allows water to run douwn in the manifold. Be sure you check both. You may be lucky and have caught a pending disaster since a bad riser will usually fill an engine with sea water ....and that never has a pretty outcome.

 

[berth control]

If you pressure test the cooling sysemt and leave pressure on it. If the manifolds are leaking, the reason you can't see the antifreeze is because it is going into the mufflers then overboard.

Try removing the large rubber exhaust tubes from the risers the repeat the pressure test. I bet the leak is obvious.
\

good idea. I never thought of pulling that boot off, makes sense. Another thought, if your leak is slow enough to just be dripping out when the manifold is cold, the system is big enough to hold pressure for a couple hours and still be dripping out the exhaust. That could be why you aren't seeing the pressure drop with the pump and gauge.

 

[dpmulvey]

Same problem in Saint Max. Problem was the hose connecting to the water heater. As the coolant hit the metal connection on the water heater it evaporated.

Worth a shot.

 

[lucknow]

Thanks Eric,
I will try to remove hose at heater and recheck for a leak. The exhuast is thru hull and i have straight drive inboards.

Thank you also, Frank, I will remove the exhuast hose and reinspect. I will try it both while hot and cold. I have a pressure tester and hope i can see coolant in the exhaust. If not i will try to swap them, at least it will rule them out if it does not reveal the problem.

I'll keep you posted
Kevin

 

[lucknow]

I can't believe this is still going on, I have tried all listed suggestions, i even replaced the riser gaskets to manifolds and the leak is still present. I am currently losing about 1/2 gallon of coolant after 3 hours of running. If there is anyone with more suggestions please let me know.
All of your suggestions are greatly appreciated.
Thanks Kevin

 

[PlayDate]

Kevin,

There are only three places it can go: 1) Bilge 2) out the exhaust 3) into the engine

1) Obviously it is not in the bilge.

2) You have already swapped the heat exchangers which was smart and checked the manifolds/risers. I do use a dye leak indicator to ensure that it is not in the exhaust system. It is a dye that you add a few drops to the antifreeze and it is visible with a black light.

3) Leaking head gasket or block/head crack could also explain the leak although you would have a sweet smell at the exhaust and more steam if it was finding it's way slowly into the combustion chamber. At half a gallon you would know if it was finding its way to the oil plan. Still, I would probably get the oil tested since that could also lead you to where it might be going. I would also do a compression test to eliminate a head gasket or crack issue.

I know it is frustrating......normally it is the exhaust system or the heat exchangers that are at fault.

-John

 

[mistercomputerman]

You may want to check to see if the boat also has transmission coolers and/or oil coolers which are similar in natue to the heat exchanger.

A transmission cooler leaking would allow the coolant to mix with the transmission fluid probably causing a sheen on the water out the exhaust. A bad oil cooler may act in a similar manner.

Maybe a pressure test overnight?

 

[lucknow]

I am also an ASE certified tech.
Thanks for the comments, Does the black light show signs of dye at discharge port?

The motors do have transmission and oil coolers, no signs of cross contamination in either.

I have not done a compression test, the plugs show no signs of coolant entering the cumbustion chamber and the engine runs great, so i do not believe it is that, however I have been wrong before "ask my wife" ha ha.

I appreciate the suggestions and i will keep searching, the day i find this I am buying the beers, maybe I'll send some to all posters who helped me out!

Thanks
Kevin

 

[johnsross3]

I'm just wondering whether an elusive and slow leak like this might be resolved at least temporarily by adding a radiator stop leak to the anti-freeze? Obviously, its a band-aid, but could this cause any other problems?

Elsewhere here, I read a post where the owner complained that Mercruiser exhaust gaskets are notoriously problematic. Anyone have experience where they resolved a slow leak like this by replacing the exhaust gaskets?

 

[J Levine]

I'm just wondering whether an elusive and slow leak like this might be resolved at least temporarily by adding a radiator stop leak to the anti-freeze? Obviously, its a band-aid, but could this cause any other problems?

Elsewhere here, I read a post where the owner complained that Mercruiser exhaust gaskets are notoriously problematic. Anyone have experience where they resolved a slow leak like this by replacing the exhaust gaskets?

Yes and Yes. Yes I have used stop leak in the past but only for a leak comming from the motor... a head bolt that would not seal. And yes replacing the gaskets can stop leaks like this too.

 

[SCORPIO]

I'd do the dye check, sounds like a crack in a manifold somewhere. Would it be worth it to take the risers and manifolds to a shop and have them magnifluxed?

 

[mistercomputerman]

I'd do the dye check, sounds like a crack in a manifold somewhere. Would it be worth it to take the risers and manifolds to a shop and have them magnifluxed?

Not unless you could get it done really cheap. Manifolds and risers are regular, replaceable, maintenance items every few years depending on your boating conditions.