6BTA5.9M 250HP temperature creep

[glenn maerki]

twin 1989 6BTA5.9 250 HP CPL 953, 1760 hours

Having a temp problem on port engine. Coolant temp creeps up as I run, If I run about 2200, the port engine temp will gradually increase to 175. At 2250 it will creep to about 180 and at 2350 it creeps up to 185 or so and then I’ll pull throttles back and it cools off. Very repeatable so I don’t think this is a gauge/sendor issue. Stbd. engine runs about 165 and will stay there all day long no matter what RPM I run.

I have Tony’s 160 deg thermostats. No other coolant upgrades. corner expansion tanks, do not have TA recommended 1 inch banjo and hoses etc. I can see TA shaking his head already. Both engines always ran the same temp. I put new SW impellers in this season. Heat exchangers were changed several years ago and I descaled both engines a couple years ago.

The port side overflow tank ended up about 1 inch higher even after the engine cooled down and the expansion tank was low on coolant. the stbd engine overflow tank went right back to normal level after the engine cooled down.

I pressure checked the coolant system cold with a STANT pressure tester and it holds pressure. The rad cap is fairly new as well. I’m not sure if the 2 issues are related….

thoughts?

Topic

[Francis Valerio]

That is great news!

It is very important that we ALL follow up on our threads. Others will use these threads to search and help troubleshoot future problems. We are fortunate to have people like Tony and Rob (and others) that give out free advice. Marine Diesel knowledge is probably the most expensive knowledge one could acquire.

[glenn maerki]

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FINALLY!!!! Just got back from a 40 mile run with the fleetguard restore plus and with the new 180 deg. t stat. Engine came up to temp with a little overshoot to about 185 deg, i could see the temp drop off when the t stat opened and for 40 miles at 2400 rpm the temp sat at 181-182 degrees. no creep. must have been that t stat all along.

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Hunter Begnaud

[Rob Schepis]

I think it’s overkill to have both and if they have been empty for 21 years I think you have proven that the south bay is doing it’s job and all you need. I’m south bay’s only and never anything in the bottom of my after cooler, heat exchanger, etc. Would be easy enough to double check that cork gasket and add some grease or rectorseal or the like to it. Yes I would be surprised if you had a bad impeller too but it can and has happened where an impeller gets spun on it’s own hub. Trying to think a bit “out of the box” here as you seem to have covered everything “in the box”…….

[glenn maerki]

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I put brand new cork gaskets on the strainer lids this spring. Typically do not grease the lids but that might be a good idea?? i do run baskets as well as the south bay strainers. I’ve never seen anything in the baskets in 21 years of running this boat. You think I should run without them? as I mentioned the impellers are both new. Would be surprised if it went bad already… really have no time on it since I’ve been chasing this problem. pumps aren’t bad as far as access…the tight area i was referring to is where the oil cooler is. I could pull the pump and recheck the impeller or maybe just swap pumps..??

[Rob Schepis]

Things look pretty good. South Bay strainer and a basket strainer? I run South Bays as well but no baskets in my engine room. If things are that tight you may consider selling those and freeing up some room and plumbing. Do you ever get anything in the baskets? I have seen the occasional suction air leak at the baskets?

Did you double check the basket and grease up the lid gasket?

You say things are tight – How hard is it to try a new impeller or swap impellers. Could the impeller be bad and at higher rpms the impeller is spinning on it’s own hub?

[glenn maerki]

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I’ll give you a rundown of what I’ve done on the SW side:
dove under the boat to ensure the south bay strainer screen was clean. It was. i remove them every year, wire wheel them clean and put a coat of pettit barnacle barrier on them. pulled the hose off the thru hull and opened the valve…that was clean. removed the feed hose from the strainer to the SW pump- hose was clear. my salt water feed hoses are wire reinforced and show no signs of collapsing. SW pump has a brand new impeller. Pipe and 2 elbow hoses that feed SW from the pump to the oil cooler….checked and clear. No leaks at either hose. Ran rydlyme through the sw system to clean any growth. both the oil cooler and the heat exc. look reasonbly clean. I also used a wooden dowel to “rod” out the oil cooler and heat exc. found no tubes clogged. I don’t think there’s anything left on the sw side to rule out. As you well know, the SW cooling system on these engines is as basic as it gets. I’ve attached a couple pics…strainer hose, coolant recovery bottle and the oil cooler as best I could get….very tight in there to get pics.

[Rob Schepis]

Have you verified the seawater intake is 100% starting under the boat at the pickup fitting (100% clean) , the seacock itself (fully opened), the hose to the pump (unobstructed and not collapsing on suction). Let’s see some pictures of those things, the engines and the coolant recovery bottles.

[glenn maerki]

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I’m getting ready to descale the freshwater side with Fleetguard Restore Plus. Decided to swap out the t-stat as its about the only thing I haven’t addressed. When I pulled the 160 deg. stat out, i noticed it has scoring almost all the way around. I attached a picture. You’ll need to zoom in to see the scoring. No idea if that would prevent the t stat from opening far enough to allow sufficient coolant flow. Will run it tomorrow with restore plus and then go through the flush process. will see what temp it runs at with the 180 deg stat in. any thoughts on the scoring and possible affect on cooling? Appreciate the help. I’ve spent far too long searching for the issue….

[glenn maerki]

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thanks for the quick reply Tony. I haven’t upgraded the turbo coolant line but the stbd engine has the same setup and no temp issues on that engine. I pulled the elbow from the head and its wide open….no blockage at all. seawater pump may be 6-7 years old and I just put a new impeller in. both engines had new pumps installed at the same time. I also just descaled the SW side with Rydlyme as part of this issue. also push a rod through the tubes on the oil cooler and no blockage. none of this makes any sense.

I’m thinking of descaling the freshwater side again (Fleetguard restore plus) ….that hasn’t been done for about 6 years or so but both engines have always had the same maintenance protocol. the stbd runs at 165 all day long no matter what the load/rpm.

what is your thought on running without a t stat?

[Tony Athens]

No issues with the 160 Stats.

1) Did you upgrade the line /fitting from the block to the turbo?

2) How old is the entire seawater pump?

3) When was the last time the seawater tubes in the HX were descaled using a 10:1 HCL/ “pool acid” mix with water?

[glenn maerki]

still chasing this

so I’ve been through the entire cooling system at this point and still have same issue of temperature creep when running higher load/rpm. The only thing I haven’t ruled out is the thermostat. I bought the 160 deg. stats from Seaboard maybe 3 years ago and have limited time on the engine since. Two questions:

1. I’m thinking of pulling the thermostat and running the engine without one. Are there any concerns with doing that?

2. Tony – have you had any issues with the 160 t-stats. I’m just guessing that maybe its not opening enough and restricting coolant flow?

at this point, I’m out of ideas and really don’t want to start throwing parts at it. Appreciate any input. Thank you!

[glenn maerki]

Temp creep

That’s an interesting thought…..debris in the intake hose. Hadn’t considered that and easy enough to flush out. Upgrading the coolant system is not the problem though….both engines had adequate cooling systems and the stbd is running perfectly with the same system. Don’t disagree that upgrades are better….but something is wrong. That’s what I want to identify and fix.

[donald roth]

Your creeping temp could be bits of old shepredded impeller hiding in the raw water system. They can be especially elusive when they’re in the pump intake line, often don’t get sucked up to the pump grating until higher rpms, and fall back down when rpms decrease.
Sounds like you already know what your engines problem is, it needs a new bigger expansion tank, And to relocate/ upsize the turbo feed, and maybe even an upgraded pump in addition to the other items you mentioned.

[glenn maerki]

still chasing this

I removed the elbow that feeds the turbo and it is clean. Used a borescope to look inside the head (can only get in a short way) but I don’t see any buildup/blockage whatsoever. There’s clearly no restriction there. I do have a spare freshwater pump and am thinking of throwing it on as I have the coolant drained. Has anyone ever had one of those pumps go bad?

[Tony Athens]

YES !

[glenn maerki]

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so Tony, the elbow into the block should be 3/4 NPT X 1 ” hose barb correct? the new banjo is 1″ hose..?

[glenn maerki]

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gonna switch port and starboard caps and see if there is a change

[Rob Schepis]

Replace the cap – sounds like the vacuum/vent feature of the pressure cap is not functioning.

[glenn maerki]

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any thoughts on why that engine is pushing coolant into the overflow tank and not pulling it back in when it cools down?

[Tony Athens]

Scale and rust at the block fitting that feeds the turbo is #1 as to slowing the total coolant flow. That should be #1 on the list to upgrade if the seawater pump is up to spec.

[Author]

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