Oil Leak at manifold/block gasket??

[bobk]

:eek: I think I have finally located the leak that I posted about some time back. It appears to be coming from the gasket that seals the exhaust manifold to the block. Is this possible? It leaks only when underway. I was able to tighten up on the bolts a bit, but the leak continues. How big a job is it to remove the manifold on a 6V92TA 425 HP engine? It is in the inboard manifold on the starboard engine so access is not bad. Do I have to break loose the riser?

Bob

[Boss Lady]

Removing the manifold is not hard to do. I am puzzled by your title, do you have an oil leak or an exhaust leak? If you need to replace the exhaust gasket, I don't think you can get enough movement if it is still attached to the riser to clear the studs and put in another gasket without breaking the riser loose or remove it.

[Genesis]

If its an oil leak its not coming from there. There is no oiil pasage to that area.

It is PROBABLY coming from the cover on the head - there's a small oval plate there, and they have a habit of dripping. It runs down the block and looks like its coming from the manifold to block interface. Its not. That one is a tough one to fix. It can also be coming from the valve cover gasket, which likes to leak too after a while.

If its an EXHAUST leak in all probability you have eroded the surface and are in a world of hurt. Those manifolds are cast iron and difficult to resurface successfully. Best bet there is to remove it, replace the gasket, and use Silkolene to attempt to seal it. May work, may not - but the alternative is not going to be cheap.

DO NOT overtighten the bolts holding the manifold on! Get the torque spec for them (its LOW - like 25ftlbs or something similar) and DO NOT exceed it! If you can't seal the exhaust with the spec'd torque then either the gasket is bad, the surfaces are eroded or the manifold is warped (!).

You have to drain the cooling system part way and remove the hotpipe bolts to get the manifold off. Both the hotpipe (riser) gasket and exhaust manifold to block gasket should be changed when disturbed.

[bobk]

Sorry to be so long getting back to this. We have been cruising without internet access.

I do mean OIL leak, and it is coming off the underside of the exhaust manifold between the first and second bolt as well as at the aft end of the manifold. Some of it puddles around the last bolt.

I do not think it is from the valve cover gasket, although I cannot tighten that any further.

What is the other point, the cover on the head and small oval plate? I don't recognize the term, but it sounds feasible for the leak source. Where is it located and what is the fix?

Bob

[Genesis]

On the side of the cylinder head are two small covers. On a turbo one of them will have a pipe going through it on one of the heads that leads to the fuel modulator (the other end of that pipe connects to a hose that goes to the airhorn to provide pressure sense for the fuel modulator)

These are notorious for leaking as the cover plates get distorted a bit and then don't seal cleanly on the cylinder head casting. Also, the holes are not blind and oil can leak through the bolt hole penetrations, even if the gasket is sealing properly, then down the head and into the manifold area. The valve cover gasket is also prone to leakage; you can't tighten it any more but the rubber inserts in the top of the cover can be replaced with new ones (that are less compressed, thus increasing the pressure) and the valve cover gasket itself can also be replaced with one that is less compressed.

It is a virtual certainty that the oil is NOT actually coming from the bottom of the manifold or the block in that immediate area - there are no oil passages there. Its coming from somewhere else.

Clean the entire area VERY WELL (using a toothbrush and solvent if you need to) and then observe it closely to see where the oil is coming from. You'll find it..... Oil leaks are sneaky on these engines (from experience!) - they often appear to be coming from somewhere other than the actual source.

[TedZ]

Sounds like typical wet stacking Detroits do so well. Have you been cruising at low cruise for a long time?

When you first start it feel for exhaust leaks. If chunks not obviously missing, tighten the bolts, run hard for an hour (without overheating). If that doesn't do it replace the manifold gadket.

Ted

[yachtsmanbill]

I'm glad you brought that up Ted ! Wet stack is a whole other topic. My MILLER BIG D II (Perkins 104) has a sticker right next to the throttle:
"if engine is to be run all day burn one 1/8" rod hourly to prevent wet stacking". Diesels even at WOT need to be loaded to make heat.
Carbon and unburned fuel is like black penetrating oil with blower pressure behind it--and you know where it will appear. 1000 rpm sounds kinda like...
New gaskets mite only "mask" it. At 1000 rpm all day as normal, I would consider dropping down an injector size. This may also help keep EGTs up as a side benefit.
AND NOW--everybody pay attention !!! Yesterday I went to our YTS (yard tug-small) with a 6-71 N. Cranked it over at a good speed and no start. Ambient air was about 35F. ONE small shot of ether and she fired right up with NO- ZERO- NADA smoke whatsoever. Looking at the dry exhaust system stack, you couldnt even tell it was running. This is on a graymarine with a 5000 hour inframe with a fresh set of RELIABILT injectors. She sat semi exposed to the elements for 10 years too!!
Ran it dockside for an hour and it didnt even make 100F on the gauge (new / mechanical) with 60PSI on the lube oil. I thought that was pretty darned good.
... And the meek shall inherit the earth... ws

[bobk]

Gentlemen, I think I'm hearing that there could be two possible issues here. Yes, I do run at slow speeds, but the lack of smoke and reasonably high coolant temperature has left me comfortable with doing this. But I'm a neophyte with Detroits so need all the help I can get.

The leak looks like engine oil. It's black, and viscous. I'll check out the covers this afternoon to see if I can confirm Karl's idea. Earlier I thought this was coming from the plates over the coolant passages that are used to link coolant systems together when the blocks are linked, so it sounds like I'm in the right area.

I don't understand how wet stacking would show up at the manifold/block interface, but then I really don't understand wet stacking. Is there a simple way to confirm that what I'm seeing is oil vs wet stacking?

By the way, I took some pictures of the leak, but can't figure out how to post them. If pictures would help in the diagnosis, I'll work harder on getting the pictures attached.

Bob

PS, how would a smaller injector raise exhaust temperatures? Sounds counter intuitive.

[yachtsmanbill]

If you have a wet stack LEAK, youll get black water (condensate) at the joint until it warms up. That may only last a minute until it dries and the joint swells shut from expansion. If that clears up to NOTHING its probably not a wet stack CONDITION. Wet stack is unburned fuel and exhaust carbon lining the system. It looks like black penetrating oil-THIN. With blower pressure it will find the minutest of leaks. IMHO, if it is hot enough the liquid will burn off and "COKE" the joint closed. Jacket temp is a poor indicator of this.
Its akin to creosote lining your chimney from burning pine vs. oak. If you follow a semi through the mountains at night and he is running on the governor with an 80,000# load you can see a steady blue flame out the stacks-- that is OPTIMUM exhaust gas temperature range. That wont happen at 55mph either !
On our big tugs, its neat to see the stack lite off at nite and throw fire out 2-3 feet. Thats on a 14 inch pipe. This only happens until its burned clean. 5 hours of jossteling around the harbor and then put the load to it picks up the stack temp, you can tell she likes the "sweet spot".
If it seems "viscous" it is more than likely a lube oil leak. Dont be surprised if the leak occurs 2 feet away and runs down the block to a convenient spot to drip off of. If it really bugs you, florescent dye and a blacklite will CONFIRM who what where why and when. IT IS AN INSTANTANEOUS TEST ALSO.
I realize this may seem like old school technology, but face it, Detroits ARE old school. Just got a cramp in my typin' finger and need to go get breakfast.
I'll be back later for some input! ws

[REBrueckner]

One of my 8v71TI's has a similar, but tiny, black ooze between the exhaust manifold and block. I take it to be an exhaust leak. As best I can tell it comes from the gasket seal, not the valve covers just above. The other engine was disassembled and new gaskets used and that one is clean. My mechanic recommended not worrying about a few drops of ooze. He said that the risers need to be disconnected from the exhaust manifold, as noted above to permit removal of the exhaust manifold, and that those bolts were prone to breaking and potentially time consuming to fix.

I, too, do not know if this represents "wet stacking", but I do run a lot at moderate RPM..about 1300 to 1500 RPM normally. Explanations would be appreciated.

I saw suggestions posted somewhere on SAMS on how to remove those riseer bolts but don't recall...maybe heat? maybe impact? tightening slightly before loosening??

[yachtsmanbill]

A pyro or therm gun will tell the truth. I run mine at 1400 - 1600 and as of yet havent seen any indications of a wet stack. X X <<-double crossed fingers!
The worst part of the WS condition is also that the lube on the rings is thin and will promote wear. Of course the "SUB" has bailing wire wrapped around the slugs for rings LOL ws

[Boss Lady]

Wet stacking is a problem expecially during the run-in of new or rebuilt engines. If the engine is not pulling a great enough load during break-in, the un-burned diesel fuel will prevent the rings from properly seating when it carbonizes and forms a tar like substance.

Running you engines at low rpm or lightly loaded in the case of a generator will cause low cylinder temperatures and wet stacking occurs. This is an accumilation of unburned fuel that slowly boils off the more volitile components leaving the heavier hydrocarbons, these will coat the piston, valves, rings, etc and even be blown into the exhaust. This can be a real problem if you habitually operate under low loads. The easiest remedy for this is to operate at 70-80% full load periodically to burn off accumilated hydrocarbons. No repairs or tools needed, just run the boat above hull speed for until temperatures are normalized every everyhour. The main thing is to get the cylinder temps up where this stuff will burn off.

The generator banks we operated in the Army all had load banks (resistive loads) that were switched in and out of circuit to stabilize the loads on them. We kept them at 50% load or higher this way. We never had a problem until the some genius convinced the Army that load banks were not needed. We had nothing but problems with generators for the last 15 years. I have seen first hand what happens to lightly loaded diesel generators.

[Genesis]

Its all about cylinder and exhaust temperature. As noted pyrometers will tell the tale for certain.

But if this is "oil", not a coke-like substance, its probably NOT wet stacking related.

Whether a particular Detroit does it depends much on condition and how its run. Injectors in less-than-good shape (bad pattern) tend to promote it as does poor oil control. You need enough heat and piston speed to insure that what goes into the cylinder burns and is ejected as exhaust rather than sticking around inside the bore.

[bobk]

A pyro or therm gun will tell the truth. I run mine at 1400 - 1600 and as of yet havent seen any indications of a wet stack. X X <<-double crossed fingers!
The worst part of the WS condition is also that the lube on the rings is thin and will promote wear. Of course the "SUB" has bailing wire wrapped around the slugs for rings LOL ws

I have an infrared gun. Where do I point it and what temperature should I be looking for?

Bob

[REBrueckner]

Good question on an infrared therm gun....I have one and would like to check. What temp ranges are good,bad,ugly??

[yachtsmanbill]

Personally, I would run several scans-- warm idle, no load full speed and several under varying load / speeds. Ns or turbos influence this also. Write them down. Full load temps vary with the quality of fuel, atmosphere, and elevation. 850 -1100 F is in the ball park. These numbers are on a dry system. Numbers may be a little lower due to heat dissipation through the castings etc.
To put this in perspective, take a look at the manifold joint in the dark at full load-- you will notice a slight cherry red after the head. This is about the 1100F point. Any more than that and the timing is late. Kinda hard to do on a DD. Maybe on one port, but if all were that hot, the guy doing the injector timing was out of it!
To get the best full load temps may require a 15 minute WOT run. This will allow all the junk to burn off as well. Internal carbon will influence an external reading. Its an insulator. The scans should be checked at the exhaust manifold immediately after the head and well before any water passages. This is where the EGT thermocouples would be placed.
This is all based on stationary generator / pump units which are typically dry systems and easy to get around when on line. ws

[Genesis]

Can't do on a boat, as the manifold is fresh water cooled. If you see 1100F on one of those manifolds (1) your boat is on fire, and (2) your exhaust valves have melted and are long since out the exhaust!

Pyros are your best bet but the tap for them is usually AFTER the turbo. Not so good, but the best you can do given the constraints of the installation.

[yachtsmanbill]

Get out yer crackilator! Found this worthwhile-- ws

Why is it necessary to monitor the EGT?
It is common believe that EGT on Diesel (especially Turbo Diesel) engines that exceed 720 degrees
Celsius, may cause permanent engine component damage. This may vary slightly as different
engines are made from different alloys that have varying heat properties. The rule of thumb is to
keep EGT below the 720deg C mark. Under normal driving conditions the EGT may vary between
250 to 680 degrees C. It will increase when driving up-hill and may even pass the "safe-point 720
deg C" if you really push the motor hard.
What happens if the temperature goes much higher than 720deg C?
Although there is no immediate explosion or melting of the engine visible, to your disappointment
maybe, it shortens the life of the motor. Again, this is all relative to the periods that the engine is
exposed to extreme temperatures. Keeping your foot down while the EGT is climbing past the 750
mark may result in smoke escaping somewhere that will send you of to the bank manager soon.
EGT is a direct indication of how hard the engine is working, so when you release the accelerator
pedal the temperature decrease immediately.

[Genesis]

Note that this is a "before turbocharger" measurement.

Measuring after the turbo, which is commonly done with marine engines, will produce a number 200-300F LOWER than the before-turbo number. Unfortunately, it is not possible to determine exactly how much lower.

1300F is way too hot for a Detroit. Detroits push LOTS of extra air through them (for scavenging) and thus don't run as hot as 4 strokes on the EGT. If you see an 1100F number on a Detroit after the turbo, things are not doing well inside AT ALL!