Diagnosing Possible Head Gasket

[pwrobert]

I installed a pair of 5.9L 6BTA 370’s back in 2019 which now have 520 hours.  Both engines seem to run well and do not smoke.  The Starboard one fills the Recovery bottle after running up on plane for a few minutes.  The engine never gets above 165-170F throughout the throttle range.  Quickly cools down to 150ish at 650-850 RPM.  But when I let it set it does not suck the coolant back into the expansion tank.  I see no milkyness in oil or altered oil level.  Tried a new pressure cap on the tank.  Ran it again for 20 minutes up to 2200 with the same result.  I see no coolant in the bilge and don’t see fluid dripping fron any hoses while running.

EGT reading are the same as when installed last year 850 Port 925 Stbd at 2200 RPM.

Is there any possibility other than a blown head gasket?  Where else should I check if this is not already a done deal?

The Recovery Resivior is mounted in fron of the engine at the same height as the Expansion tank.  Same for the Port engine where there has not been an issue.  I did put new blue silicone hoses on both the tanks as recommended a little while back on this site. Checked the hose clamps. Ok. 

Topic

[Rob Schepis]

Clamped hoses.

[pwrobert]

Final Thoughts

If I were doing this upgrade again from scratch, I would use 1/4″ blue silicone hose instead of the 5/16″.  This because normally barbed fittings have beads or ridges larger than the ID of the hose they are fitting.  Example 3/8″ hose fittings have 3/8″ main body with barbs, beads or ridges 15/32″ (almost 1/2″) and other sizes do something similar.

The Cummins overflow bottle fittings is 5/16″ OD of the ridges so a 5/16″ ID hose will always be a loose fit.  The thinner diameter between the bards is closer to 1/4″.  In this case it is compounded by the extra softness and stretchiness of the silicone hose.  I suppose most people don’t have issues with these bottles because thay are likely using standard vinyl or heater hose wich is stiffer.  

 

1 user thanked author for this post.

Tony Athens

[Rob Schepis]

Thanks for the follow-up.  Great outcome!  Yes, always good to go backtrack as you did.  When I used the 5/16″ silicon hoses I secured them to the recovery bottles with small hose clamps to ensure a tight connection.  Snugging those little clamps has just been added to my spring commissioning list!

[pwrobert]

Follow-up

Well I pulled and tested the heat exchanger and it pressure tested just fine.  Flushed and replaced the coolant and ran again with new expansion tank cap.  All same results.  Rented a pressure testing kit for cooling systems and checked for leak down and tested for exhaust in the coolant all came back just fine.  Remounted the overflow tank a few inches higher.  All with no changes.  Engine continued to run just  fine and had no overheating issues.  My engines are setup with three temperature gauges and senders- one to a Noland NMEA device for showing on the chartplotters, one to standard Teleflex Heavy duty Series gauges and one to a digital CruzPro MaxView 110.  One sender at thermostat port, one on T-off top of manifold, and the other at the left side of the rear of the block below the trans cooler.  All read normally.

Just coolant overflow tank fills and won’t return to expansion tank.  Hassled around with it for several days before I went back to Zero.  Then remembered that the problem started when I changed a while back to the blue silicone hoses as suggested on another thread here.  Before that I had the regular clear 1/4″ vinyl hoses that were put on when I bought the overflow bottles back in 2019-20 from the SB store.  I remembered that the nipple on the bottom of the overflow seemed short and skinny so I took the hose off again and drained the tank.  Took the tank to the shop and measured the hose and nipple and the hose ID was slightly over 5/16″ and the nipple OD was just under 5/16″ and there was no “press fit” feel like you get when  putting it on.  

So I fitted 3 pieces of heat shrink tubing to the nipple making it right at 3/8″ after heating with an electric heat gun.  Cut back the hose 1″ and fitted back on the nipple and reinstalled everything with the same SS hose clamp.

  After running the engine with the coolant expansion tank filled to 1 inch below the neck and 2 inches in the overflow tank (marked) watched it rise in the overflow as expected.  The next morning the overflow was back down slightly below the marked level and the expansion tank was full to top.  Problem solved.  

Even with no fluid leak at the overflow hose connection it was allowing air to get through and break the vacuum.   

Well I did get a good clean out of the engine and repainted the HX with Awlgrip while it was out and put on a new Seaboard Decal while I was at it.

[pwrobert]

Final Closure I hope

Ok. I finially tracked it down as a leaking HX.  SMX Water pump pushed ou the coolant to the Resivoir and would not drain back as the coolant leaked back down with out enough vacuum to pull coolant back into the engine and out the HX.

[pwrobert]

My new suspicions after run today

I put things back together and filled the expansion tank up 1/2 way and put a couple inches in the recovery bottle.

Cranked the engine and let it run at the dock for  a few minutes (5-8) and the engine warmed up to about 125F.  Cracked open the cap on the tank with the engine running at 700 RPM and it gushed out coolant.  Closed it down and wiped things up and let it cool a few minutes.  Gauge still reads about 120+.  No gushing and the coolant level is almost full – just below the filler neck by 1/2″.

Now I think the problem is in the heat exchanger with a leak between fresh and salt side.  When engine runs and the SMX pumps puts out raw water it crosses over and keeps the tank full – hence no overheating while running.  Hard running at 22-2300 RPM yseterday showed vigorous overdflow into the Resovoir without bubbles.  When the engine is off the coolant drains since SMX is not feeding it and the vacuum is lost out the HX into raw water hose.  Hence no return from the Resivoir.  

Next job is to pull the HX and see if it is worth testing or just replacement.

Anything I missed or am I on the wrong track?

[pwrobert]

After run at cruise

Ok I took the boat out for a run yesterday afternoon with the expansion tank full and the hose in a bucket with coolant covering the end of the hose.  Idling out for 15 minutes to the channel at 650-800 rpm there were a few litttle bubbes that went away.probably entrapped air since the level had gone below the tank before refilling.  Then when I watched the hose while the boat was put on plane and run at 2200 rpm the bucket had a few more bubles but a large rush of fluid churned up the bucket coolant until 1-1/2 quarts was added to the bucket.  Then no additional fluid rise and no bubbles entire time the boat was run – about 45 minutes.  Engine temperature was within normal the entire time 165 F max.  I have SMX Tstats in both engines.   

Came back to the dock and the coolant level in the bucket remained the same as the engine temp dropped to 145-150F.  I elevated the bucket some when I arrived at the dock to help any suction back into the engine if it was going to try. In a position lower than the overflow bottle mounting by about 12 inches.

This morning the coolant level in the bucket stayed high with the 1-1/2 qt still there.  The tank was essentially empty with just a little wetness on the bottom.  It’s like the vacuum is not pulling the fluid back into the tank.  I find no leaks anywhere.  When the 1-1/2 qt is put back in the tank it brings it close to full level.  

I have tried two different tank caps – one at 16 lbs and the other at 13 lbs.  same results.

Any suggestions.

 

[Rob Schepis]

“wondering if the 5/16” silicone hose is too large ID”

^Not sure what you mean by this?

[pwrobert]

Additional info

It was suggested to refill the expansion tank and put the cap back on. Remove hose from recovery bottle and put the end in a bucket of water. <br />Run the engine and look for bubbles. <br /><br />

I did that but had to remove the blue hose as it was too short. Put on another 1/4” fuel hose scrap piece to reach the bucket. Ran at the dock up to 1500-2000 for 20 minutes and no bubbles at all. <br />am wondering if the 5/16” silicone hose is too large ID. <br />im going to try later today to run it under load and see if bubbles reappear. 

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