6BTA 370HP losing coolant with heavy white exhaust

[Kyle Routh]

Two mornings ago as I was performing my pre-run checks, I noticed the coolant overflow reservoir on my STBD main engine (SN:46174828) was empty.  I checked the main reservoir and it was completely filled.  So I started looking for external leaks but could find no evidence of an external leak anywhere.

 

I turned to looking for internal leaks and checked the oil and transmission fluid but neither had any abnormal level or visual indication of contamination.  At this point I was thinking I probably had a heat exchanger leak and was slowly losing coolant to the seawater side via a tube/sheet leak.  So I refilled the overflow reservoir, warmed the engines then started our cruise at 1050rpm @ 7knots, our typical cruising speed.

 

Within 10 minutes, the STBD engine started producing thick white smoke from the exhaust – and a lot of it.  I went and verified the coolant overflow reservoir level and I could definitely see that the level had lowered.  Typically I see level go up an inch or so, but it had dropped about a quarter inch.  Given the lowering level and thick white smoke, the heat exchanger leak seemed less likely.  During all of this, temperatures were normal at the helm indications (165F) as well as temps taken locally on the engine with an IR gun.  I was comparing them to the PORT engine and both were as matched as they ever are (within a couple of degrees).

 

We continued to slowly make our way and I kept checking the overflow reservoir every 5-10 minutes and could definitely see a lowering trend, but nothing drastic.  The white smoke sometimes got a little less, and sometimes would get worse.  Finally, I saw the helm temperature start to rise pretty rapidly and I turned off the engine immediately as the temp was passing 200F, but it continued to rise to around 220F before stopping.  No alarms were ever received.

 

After putting the other engine in neutral, I went down and saw that there was still coolant in the overflow reservoir, but it was lowering pretty fast as it was being drawn into the main reservoir – and it was empty within just a few minutes.  I didn’t want to open/check the main reservoir at that point as everything was pretty hot.  We finished our trip on the PORT engine and once the STBD engine cooled I checked the main reservoir and it was completely empty.

 

My research of the symptoms seems to suggest a potential coolant to exhaust manifold leak and based on research on this site I thought I would go after the two most obvious locations first: the exhaust manifold cap gasket and then the turbo charger to exhaust manifold gasket.  I called today and spoke with Marco at Seaboard Marine who helped me confirm the parts I would need (he as very helpful) so I plan to get those ordered as soon as I know where we’ll be (we’re on anchor currently waiting out weather near Key Largo, FL).

 

I am attaching pics of the exhaust manifold cap after removal – before doing any cleaning other than wiping off the gasket.  You can see what looks to be a loose sealing surface on the gasket hanging down in the pic with my hand, but there was no evidence of external leakage from the cap so I am not sure if that tear was the result of removing the gasket or a potential failure mechanism.  Also I definitely found what appears to be residual coolant in the exhaust manifold.  (I stuck a paper towel inside and it came back soaked with a yellowish liquid which is the color of the coolant I use (Valvoline Zerex G05).  It didn’t fill the manifold, just some traces of it that I was able to see.

 

I haven’t removed the turbo from the exhaust manifold yet.  I basically wanted to attack this one step at a time so I started with the cap gasket replacement (the easiest) to see if that works.  If not, I will proceed to the turbo to manifold gasket and replace it and see if that works.  If not, then I am guessing I will have to remove the manifold and have it inspected/tested.  And the final attempt would be a head gasket replacement if all else fails.

 

I know that’s a lot, but I wanted to give as much detail as possible.  My questions so far that I would like help with are:

1. Given my symptoms and indications, am I on the right track?
2. Does my work progression (1. cap gasket, 2. turbo gasket, 3. manifold removal, 4. head gasket) seem reasonable?
3. Is there anything specific I should be looking at to confirm the source of the leak or which component likely failed? Nothing jumps out at me on the manifold exhaust cap and gasket, but maybe the pics reveal something to more experienced eyes.

 

Thanks for reading and any feedback is greatly appreciated!

Kyle

Topic