Combustion gases, or exhaust getting into the coolant?

[Jen Wren]

Last winter while preforming maintenance on one of our QSC 540hp I discovered the coolant was black as coal. Tony said:

“There are really only three things that would cause this–Oil, combustion gases, or exhaust getting into the coolant and all of these would typically cause something external to be noticed”

After a few questions he suggested changing the turbo gasket which did in fact solve the problem.

Now I’m having issues with a QSB 380hp. This motor is in a charter boat that works everyday and is pushing 11,000hrs. Last week oil started spewing out of the airsep. Changing the coalescing filter we discovered the serpentine belt was shredded. About this same time it appeared there was excess vapor coming from the exhaust. The motor wasn’t over heating but I started paying closer attention to the temp gauge and noticed it was a little erratic depending on RPM.

First course of action was to inspect the intake of the gear cooler and it was clean. Next was to change the raw water impeller. Removing the plate from the raw water pump we discovered a deep circular gouge in it. With that I just replaced the whole pump. Keep in mind the boat is working everyday and we are systematically eliminating possible causes in the evening.

Last night we changed thermostat. It was no fun on a hot motor but we got it changed. Starting the motor the temp rose to 170 and than back down when the thermostat opened.

The alarming issue was the coolant is black as coal. There is no oil in the coolant which leaves combustion gases, or exhaust getting into the coolant. Anybody know of a way to determine which it is?

The head was replaced at 1,100 hrs because the exhaust was not built correct when repowered. The turbo was replaced about 4500hrs ago. The motor is strong and runs like new consuming no oil between service.

This morning we are still getting excess vapor from the exhaust. Turbo gasket, head gasket, cracked manifold? Any ideas?
The old thermostat looks bad. Here are a couple photos

Topic

[Bill Fuller]

Bill D,
He says he services the heat exchanger and after coolers every winter.
After all that has been posted my thought is to go back to basics and check the easy things first.
So,
How old was the replacement raw water pump? Had it been setting around as a spare for a long period of time?
As a next step, I would simply replace the impeller in that pump and see what happens.
Bill F.

[Bill Desmarais]

you’ve isolated just about everything.

You have very warm water trying to keep the engines @ 180 F.

11,000 on the engines ? Remarkable and you’ve taken care of both.

One last question?

Knowing that the boat is used as a “daily charter”…..have either of the heat exchangers ever been taken off the engines, “cleaned and “boiled” at a radiator shop ? Maybe just maybe the heat exchanger core is slimed, oiled, calcified, whatever?

The cooling systems on your engines have to be 110% perfect with water temps in the high 80s.

Just a thought ??

Keep us posted,

Bill D

[Jen Wren]

Thanks Rob,

I don’t like or trust an ir gun but have become desperate. I tested the areas over and over to try and find consistent readings resting my hand on something trying to create the same angle each time.

The raw water intake hose is a good idea but ours is very heavy walled and in good condition. Also from my photos you can see good water flow out the exhaust.

I have been through a lot trying to find the problem and hate to pull the top end off on exploratory surgery and not find anything.

[Rob Schepis]

Be careful with the IR gun for small variations – how you shoot the target and it’s surface type/finish will effect the readings, especially if shot on an angle.

Have you investigated/verified that the steaming engine wet exhaust is hotter than the non-steaming side? – using an IR gun and your hand downstream in the wet piping and at the transom outlets?

Didn’t see this mentioned but maybe I missed it – What’s the condition of the hose between the seacock and pump? Could it be partially collapsing while under suction?….

[Jen Wren]

More info

Just read my post and left out some important info. It has been a little hectic with Tropical Storm Lidia knocking out our services for a few days.
Sea temp here is 86 degrees. When I did the IR temp testing we were cruising at 2500 rpm. Temp gauge on both motors was reading 180 degrees. When throttling up beyond 2500 rpm the temp gauge and the starboard motor rose very quickly to 190 while the port stayed at 180.

Seems like a blown head gasket or burnt valve would show more signs then we are getting. There is no oil in the cooling system and it is maintaining a full level. Cracked exhaust manifold? Beats me? We have been operating like this for more than a month now and need to find the problem before something catastrophic happens.

[Jen Wren]

Going to my head

Got in the engine room and snooped around with a IR temp gun today. Most points seemed the same tempurature on both motors until I notice the exhaust manifold on the starboard motor was 7 or 8 degrees warmer than the port which I didn’t find really alarming. Almost ready to give up I started hitting the cylinder head near the area where fuel lines enters from the common rail. Most cylinders were around 150 degrees but the number six cylinder on the troubled motor was 165.

Tony, throw me a bone here. Head gasket or more serious?

[Jen Wren]

Thanks Philip. Yesterday I got out my IR gun and changed the battery. I had not seen Tony’s IR gun Temp check. It will be a good guide in where to check. I’ll bring the boat up to cruising speed and compare both motors.

[Philip]

If your concerned the sensor/guage may be an issue an infrared laser thermometer is very useful to take temperature readings while underway of both engines…

IR Gun Temperature Check

[Jen Wren]

Philip,

No smoke and the motor peforms well. It keeps up with the other motor and hits the rev limiter without a strain, just 10 degrees warmer. Other have suggested the gauge is wrong but that doesn’t account for the exhaust vapor.

When we checked the raw water pump the impeller was complete. I elected to replace the complete pump because the side plate had some scoring. That was after checking the gear cooler and heat exchanger for obstruction. Looking at the exhaust over the transom both motors seem to have the same flow of raw water

We also removed the speed scope raw water intake and cleaned the inside of it. The seacock was clean.

Exhaust vapor seems like over heating to me but the temp gauge on both motors are the same at 2500 rpm. What the heck is going on here? The motor is asking for attention but I don’t know where to look.

[Philip]

1. Impellor pieces in the hose from the intake to the pump or pump to the fuel/gear cooler.

2. Sea strainer clogged, or should I say not 100% clean

3. Intake valve/seacock not 100% open

4. Need to removed fuel/gear cooler, aftercooler, and heat exchanger from the engine and get the passages 100% open with a good acid wash and pressure test.

5. Bad raw water pump – even a new one can be bad – start with a new impellor and then maybe swap left to right to see if issue moves sides.

Just some ideas

Out of curiosity do you get any smoke and/or has your max RPM changed?

[Jen Wren]

Totally perplexed

Back to the drawing board. After changing the raw water pump, coolant pump, mixing elbow, thermostat, turbo to manifold gasket and coolant the motor still acts the same. Excess exhaust vapor while cruising at 2500 rpm and temperature creep to 190 degrees from 180 when excelerating beyond 2500 rpm.

Cummins is out of ideas and I’m lost. Anybody have anything for me?

[Jen Wren]

The perfect storm

It has taken some time but we have finally sorted out our cooling problems.

It turns out we had three separate unrelated issues going on at the same time.

Excess exhaust vapor was because the raw water mixing elbow had a pin hole allowing raw water to mix with the exhaust gas prematurely.

Black coolant was caused by a turbo to manifold gasket failure where exhaust gas entered the cooling system.

After those repairs were complete the temperature on the suspect motor would creap to 190 degrees at WOT while the other motor maintained 180 degrees. Out of ideas I decided to change the fresh water coolant pump. While hard to inspect when on the motor it was obvious once we removed it. The bearing squeaked when spinning the pulley and signs of a leak from the weep hole gave it away.

Live and learn.

[Jen Wren]

Rob raises an excellent point and somthing I had not considered. My crew is very responsible but the saying goes, when the cat is away….. Having high expectations just sets me up for disappointment so it is possible.

That said I don’t know when it might of gotten hot. Seems a check engine alarm would have sounded? The motors are serviced every 100hrs. Every winter the heat exchangers and after cooler is also serviced.

In any event I have an extra head, gasket set and head bolts. Last night we pulled the boat and today we will start breaking down the top end to see what we can find.

[Rob Schepis]

“This motor is in a charter boat and works every day”…… so that means you are not aboard for first hand knowledge 24/7, right? You say it is not “overheating” but could it have “overheated” ?

[Bill Desmarais]

Is it possible the engine may have an exhaust leak @ the head/exhaust manifold mating surface? Bad gasket?

[Author]

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