6-71 running warm

[captadamr]

Hello all

Just made it back from Fort lauderdale, we had all the coolers, (fuel, after, transoil and heat exchanger) removed and cleaned, and changed the gaskets on the strainer, and even though all of these were in bad shape the port engine continues to run warm, 190F at 2200, but the stbd runs @ 175F at 2200. The Motors are 390Hp 6-71 maranized by covington.
If anyone has any other ideas please let me know

 

[Genesis]

Put some gauges on the raw water system and see what's up. My guess is that you've got a restriction somewhere. Compare against the other engine.

 

[Boss Lady]

I would check the through hull fitting, sometimes you can suck something in that will not complete clog it up and won't make it to the strainer basket or you have marine growth on the guard itself. Time to dive her and see.

 

[Passages]

Before doing the above, shoot the t-stat with an IR thermometer to confirm the gauge is accurate.

 

[captadamr]

I guess i should have said more, there is a mechanical gauge up the line from the sender for the helm gauge. The boat was hauled last week, bottom cleaned and painted, all parts of the freshwater system removed and cleaned, gaskets changed on the strainers,new hose from strainer to the pump, oh yea and 2 newly rebuilt saltwater pumps. The only thing that didnt come off was the freshwater pump (im assuming there is one). Other than that its running 20degF warmer than the other side. Unless the guage is bad and is the culprit, but i cant see the mechanical and digital both reading the same and both being wrong. The only thinng that i can guess is that the heat exchanger isnt working 100% because it keeps puking coolant out thru the overflow, which leads me to believe that there is saltwater finding its way into the freshside, but willl that create a 20deg F rise in temps.... The stbd motor has had the same treatment and runs @ 170deg F under identical load. .....never had much luck with the 6-71s.

Anyone got an idea?

 

[doc g]

If you 've got sea water in the HE, something is compromised and you are running sea water thru your block too. I believe the only thing in that system is the HE that could be the culprit as the fuel. gear(?) , oil coolers do not use glycol ,only raw water. Did they pressure test that HE when it was serviced? I would think that would be part of the deal when they cleaned it. Also I suppose that you could have a blown head gasket pressurizing the A/F side of the cooling system. If the level rises in the expansion tank with the engine running and the cap off : it's the HE. Test the A/F for salt,also..............Pat

 

[Will]

You may have blockage in your heat exchanger. If you have turbos, check the intercooler. On the other hand, water boiling out of the over flow at 190 degrees could be a symptom of other problems. Perhaps it is as simple as a bad pressure cap. If the cap is OK, you might try a pressure check on the cooling system.

Sorry about your experience with 6-71's. They are usually extremely reliable.

Will

 

[doc g]

Pressure testing is not cool as you can force coolant into cylinders and result in hydrolocking,broken rods,holed pistons etc. Can't it be vaccuum tested instead??......................................Pat

 

[captadamr]

well i thought it may have been the cap, replaced it with the one from the other exchanger and it stil leaked from around the base of the cap, not from the res vent. its weird though that it just drips slowly when the engine is running at cruise but when throttling up it has a steadier rate of leaking. other than the running warm 190F at 2200, the engine runs flawlessly, very little smoke on start or throttleing it up. The heat exchanger was supposedly tested and was ok. The intercooler was dissassembled and cleaned.

 

[yachtsmanbill]

;-B) << these are BUBBA TEETH ! When you put new hoses on the strainer were they non collapsing reinforced type? Those pumps really suck and a little squeeze on the hose can severly reduce da' flow ya know? Just another stupid idea, but sometimes we overlook the obvious. ws

 

[captadamr]

nah its the same black hose with the reinforcing metal mesh inside, thats not the problem, im going to take the saltwater pump off and check the impeller, the pumps were rebuilt by the PO, and maybe the impellers have been sitting there for a while and are messed up, if not that then im going to check the HE with the cap off, or maybe ill do that first.

 

[Genesis]

Are you running coolant or inhibited water?

If coolant, and you're getting coolant forced out at 190, you've got serious trouble. Either you have salt water getting into the cooling system from the raw water side (which, by the way, can't be in the fuel cooler - it has to be in the heat exchanger as there is no coolant in the fuel cooler) or worse, you have a compression leak into the cooling system.

Both are major emergency items that need attention RIGHT NOW. Salt water in the block will destroy it quite quickly.

If you have COOLANT in the system it has color. Start up COLD and have someone watch the exhaust CAREFULLY, or shut down and pull the raw water hoses going into the heat exchanger. If its leaking you should be able to see the green/pink/orange/whatever-color-your-collant-is in the raw water. IF you're leaking raw water into the system you're also leaking coolant out into the raw water flow when you shut down and the pressure in the system is higher. Look for signs of glycol in the exhaust water on a cold start or in the pipes as above. If no joy.....

Pull a coolant sample IMMEDIATELY. Have it tested. You will find either salt or combustion product contamination this way. You now know which you've got. If salt, the raw water system needs to be torn down immediately, flushed VERY thoroughly, the heat exchanger tested and either the core replaced or, if its a one-peice unit, the entire thing re-cored or replaced. You will not like the cost of this one bit, but its better than the other alternative which is...

If the contamination is combustion products then you have either a leaking injector tube or a leaking head seal ring. Both are extremely serious problems as coolant WILL leak back into the cylinders when you shut down, leading to either severe cylinder kit damage or worse, a hydrolock. In either case the head has to come off.

 

[yachtsmanbill]

After all that work I assumed you changed the impellers--MOST likely culprit. My 12-71s overheated due to TINY shells from dredging that packed the strainer 50%. Only O/H above 1400 rpm. AF blew out the overflow pipe (about a gallon) and showed 200F--almost critical before I caught it.
Double check the fuel cooler for impeller debris. Thats next in line on the 12s anyway. ws

 

[Genesis]

PS: 195F is "never exceed" on Detroits....

 

[captadamr]

ok, well forgive me if im wrong, but if theere is a blown gasket, or leaky injector tube wouldnt it be a constant blowout thru the entire rpm range, getting worse at a higher level. there isnt a forced stream that comes out but rather little annoying drips, like if a tap was left on. The leaks is worst during acceleration then it stops for a while and then starts again. Its not water pouring out of the exchanger but instead a series of drips, at its worst 1 dip per 5sec, averaged one drip per 10 sec.

yes we have 2 other boats with 8-71 and 6-671 nautrals. the motor didnt get to 200 before we caught it, and never exceeded 190 the run over to Nassau.

 

[yachtsmanbill]

Beggin yer pardon skipper, but my fuel coolers (12-71Ns) are fed directly off the raw water pump. Not coolant (?) hot side. On an old GMC generator set
(45kw stationary unit) I had, bad cylinder sealing was evidenced by soot on top of the glycol.
"The heat dissapating capacity of the engine cooling system and related components must be sufficient to prevent the coolant from rising above 210F(99c). This temperature must not be exceeded under any engine operating condition, regardless of altitude, type of coolant used or cooling system condition". Page 6 sect 5
"A fuel cooler may be mounted in the raw water system, between the heat exchanger and the raw water pump, so that the fuel leaving the engine is cooled before it is returned to the fuel tank." section 2.5.1 page1 under "fuel cooler".
At any rate I always try to start looking at the overlooked obvious stuff before tearing into another can o' worms that could cost Gs to put back together with less than desireable results. Call me nuts bubba, but thats just MHO ws

 

[Genesis]

No - a small compression leak will show up worst under hard acceleration (when combustion chamber pressures are highest)

Thing is, you both cannot guess here nor can you ignore this. A coolant test is dispositive - spend the $50 and find out FOR SURE what's going on. If there are combustion products in the coolant, that will tell you. If there's salt (sodium) in the coolant, it will tell you. Either way you will KNOW.

 

[captadamr]

unfortunalty there is no one here to test ther coolant, its not the USA, welcome to the BAHAMAS.Thats why i have to play the guessing game

 

[Genesis]

Can you FedEX the sample to a US lab?

Another diagnostic attempt you can make is to remove the cap, start the engine, and see if you can detect bubbles or foam in the tank. Unfortunately this is not definitive, and you won't be able to run under a heavy load with the cap off.

The third test you can make there is to go for a run (to get it good and warm) and then shut down and REMOVE the raw water hoses from the coolant tank. See if you have any color in the drained water, and whether any shows up dripping out. The system SHOULD leak in reverse (out the raw water side) if its leaking raw water into the fresh when you're running. This works best of course if you have coolant (e.g. glycol with coloring in it) in the system.

 

[Spellbound]

If in Nassau double check with Peter (Manager/Dockmaster) @ Nassau Harbor Club 393-0071 or call Marine Diesel Limited 394-2135. Finally Lightbourne Marine --- Marine Hardware store with very experienced indiviuals, asked them for help.