Logo

kamd300a exhaust elbow leaking raw water in air chamber

Bigvtwin1

Contributing Member
I went round and round with overheating issues last season and i thought i had corrected the problem ie, cleaning out the inner cooler and the heat exchanger, changing the air filter, new belts etc. But now this year I'm running hot again, around 200 deg. I pulled the exhaust elbow and found it has perferations between the air and water channels. can this cause overheating even though it is downstream from the engine ie, on its way to the exhaust, people have told me it can cause overheating. Can anyone tell me if they have had any experience with this issue? Anyone with expert advise? Anyone having the same problem. Desperate here and dead in the slip till i can correct this problem.
 
Maybe I didn't read this right but there should be performations between the water and exhaust in the exhaust elbow. The other name for that elbow is the 'mixer' because it is where the cooling water in injected (mixer) into the exhaust gasses. An overheating problem with the elbow is often that the mixing holes are blocked with corrosion. This reduces the water flow through the engine and is a very common issue on a lot of marine engines.
If the 'perforations' are higher up in the elbow than the mixing holes then you need to change it out as you could get water back into the turbo and maybe the valves as well. I can't see why 'extra' holes would cause an overheat, but the mixing holes being partially blocked could.
 
Thanks for your reply aliboy, yes i see what you are saying as long as the openings are not blocked it should be good. I thought the water jacket was just to cool the elbow from the hot gases and didn't know that it actually mixes with the water. I can't figure out why its running hot though?
 
Are all the elbow mixing holes clear? Try and find a picture of a new one to compare with. Partially blocked mixing holes are a common cooling issue on a lot of engines. Other issues could be an air leak on the intake side of the raw water pump, bad impeller, or worn pump internals. How many hours om the engine? When it gets hot an you slow down does it cool down quickly or slowly?
 
Are all the elbow mixing holes clear? Try and find a picture of a new one to compare with. Partially blocked mixing holes are a common cooling issue on a lot of engines. The holes should be quite substantial, not just look like small pinholes etc.Other issues could be an air leak on the intake side of the raw water pump, bad impeller, or worn pump internals. How many hours om the engine? When it gets hot an you slow down does it cool down quickly or slowly?
 
Yes the holes are clear no debris i shined a flashlight in the holes also ran a thin screw driver through. All clear they weren't blocked. I have 1400 hours on the engine and have replaced the wear shims once and usually change the impeller every season. When running at approx. 3200 it gets to 200 deg. pretty quick and when i slow down it cools down pretty quick. I'm not loosing any coolant thank god.
 
Is the engine on a out-drive (stern leg) or on a shaft? If it is an out-drive then another possibility is growth in the the exhaust passage through the leg (not so likely) or if the cooling water is coming in from the leg instead of a separate thru-hull and strainer then there could be some growth in the water tube or pick-ups in the leg. Other possibility would be dirty hull or dirty propeller. Are they both recently cleaned?
 
Is the engine on a out-drive (stern leg) or on a shaft? If it is an out-drive then another possibility is growth in the the exhaust passage through the leg (not so likely) or if the cooling water is coming in from the leg instead of a separate thru-hull and strainer then there could be some growth in the water tube or pick-ups in the leg. Other possibility would be dirty hull or dirty propeller. Are they both recently cleaned?
 
Yes this engine is equipped with an outdrive, to be specific its a DP-G volvo duo prop. I just launched it 2 weeks ago and everything is clean. No clogging within the ports of the outdrive no clogged strainer that comes from the through the hull. Everything is clean no growth. I'm wondering if the wear shims as you spoke about a few replies back could be worn on the raw water pump? How can you tell by looking at the plate if its worn is there a thickness tolerance?
I just got back from installing my exhaust elbow after filing the flanges and pulled the air filter to see if it was clogged and it sure was all sooted up with some signs of oil mixed within, a greasy black layer on the filter. Never had that before last year. And that filter was changed mid season last year and less than 70 hours. What kind of a sign could this be?
 
Air filter could be a sign of a small exhaust leak somewhere. This will give diesel soot on the air cleaner and then any moisture in the air will turn it into something that looks oily. The other thing to check might be how much blow-by there is on the engine. I don't know if that model recirculates the crankcase ventilation into the air cleaner or not, but excessive blow-by could cause a dirty filter if it is recirculated.

I don't know an easy way to check the wear plates accurately sorry. Maybe you can get some clues by searching online. The wear can be on the internal 'cams' or the end plates. I don't know that particular pump but do check the end plate at both ends as well as the cam. Another thing to check is make sure that there is no water leaking from the weep hole at the base of the pump housing. If there is it could mean that the seal there is worn and that could let the pump suck air and reduce it's volume. Another less likely issue if it has already been changed could be the impeller itself. Some impellers can be better made than others and some can be old stock and a little deteriorated when you get them. I imagine that the impellers are probably good for 400hrs or so (not sure what that engine states) so if you only have a few hours on it, it is probably not the issue but worth replacing when you check the pump internally anyway.

If the saltwater pump is good and the heat exchanger & aftercooler have been cleaned, plus the mixer is good, and you are not overloaded with dirty prop/hull then biggest suspects would be an air leak on the intake side of the pump somewhere or an issue with the coolant pump vanes. Does the raw water strainer stay full or if it is a glass top one can you check if the water is right up to the glass when the engine is running? The coolant pumps operate with a set clearance on the vanes so if for some reason it has started to deteriorate or if maybe the bearings are worn it is a possibility that it could cause the overheat but not very likely I suspect.
The other thing we haven't mentioned is the thermostat. Has that been replaced or can you try running with it temporarily removed (some engines can and some can't)?
 
That is a big relief about the greasy looking soot on the air filter, not being oil from the engine. I will check for air leaks and also to see if my strainer stays full when running. I change the impeller every season so thats why i thought that was good to go. I'll have to pull apart and check the tolerances on the end plate for wear and also the condition of the rubber vanes. I put that one in in August last season.....Also i have an air leak coming out of the exhaust elbow seeing the tell tale sign of the black exhaust on the housing of the turbo. Being an outward leak could that cause the problems I'm having? Also I did change the thermostats last year when i rebuilt the main water pump on the engine, ( fresh water/antifreeze ).
I must thank you for sharing all your knowledge on these issues.
 
So the 'oily' air filter is probably from your small exhaust leak. Get the leak fixed and clean the air filter to see if it is still happening. Don't forget to check if there is any sign of water weeping from the relief hole under the pump body. If that seal is leaking you could be pulling a little air through the seal. Also check that the top of your water strainer and all the piping is sealed properly. Right now the most likely thing would seem to be a water pump problem or air leak from what you have done so far.
I was just talking moments ago with a friend who recently fixed a Volvo D6 water pump issue. I don't know how similar the pumps are o yours but he was commenting about having to regularly replace the end plates due to the wear allowing pressure to bypass the impeller and reduce the flow.
 
OK I will use the boat for a few hours and see if the new air filter stays dry and clean. Check for the possibility of a leak at the weep hole on the pump and the strainer to see if the level stays full when throttling. I will also check the impeller and the end plates for wear. I could have an impeller that was old stock as you stated. I found out who manufactured my exhaust elbow that was pitting internally and they said they still had the jig and could make another one for me however the price of 2500 was way out of my range , (way out) so i made repairs with JB Weld. The repair came out very well. Haven't made a run yet though but confident it will hold up.
Thanks once again Aliboy for your great knowledge and kindness to share. Its such a wonderful tool to be able to work out a problem for someone who wants to and has the ability to make repairs themselves to be able talk to someone like you when you don't know what the real problem is.
 
Your welcome for any help. Will be really interested to see what the fix is. Just re-read this thread to check for more ideas. You said you rebuilt the coolant pump last season. They can sometimes be very tricky to get all the vane tolerances set up correctly and the mechanical seal installed if it is like the other I have worked on. Are you confident that the vane to housing clearances are within spec as this may reduce the flow rate? This is probably a less likely problem but worth discussing at least.

What material is the elbow made of? I assume you had to get a custom one made to fit the boat by the sound of it?
 
Yes, last year i rebuilt the coolant pump and was careful to get the tolerances correct. Using a metal straight edge against the flange housing of the pump and a feeler gauge between the impeller vanes to the right specs as stated in the manual for my engine. Im confident the pump is putting out the correct flow. The elbow is stainless steel and i didn't replace it as they were so far out of my financial range of 2500 i made repairs with the JB Weld and is restored almost like new. Tomorrow I should get some results with all things i will be following up on. What puzzles me is that when i took the boat of of the water for the season it wasn't running hot and the first time out this season it starts running hot. Maybe since the rubber raw water impeller sits in the housing all winter all bent up and not being turned at all for 4 months it could be cracked and out of shape. Thats what Im hoping anyway.
 
Just as a note, you can get replacement exhaust elbows in the standard Volvo configuration (i.e. if you don't need a custom shape) for ~$450 + shipping

https://www.marineenergy.com.au/pro...289-stainless-steel-elbow-replacement-hdi-vg1

$2500 for a custom stainless one sounds about normal unfortunately so if you do need to change it I would check if you could buy the off the shelf one and get it modified rather than building one from scratch. Should work out a lot cheaper if it is possible.
 
Thanks for the website for the elbow. I sent an email off to them. The one shown in the pic says it is used for several engines and mine is one of the ones it should fit however mine has a 180 deg. bend and the ones i have found on the web in various sites all have a 90 deg. bends. Anyway just pulled my seawater impeller and your right the vanes were all cracked and almost apart. Installed a new one tightened both the compressor and coolant pump belts and ran a good half an hour at cruising speed. The elbow is no longer leaking and the temp only dropped about 5 deg. now running at 195. Is this acceptable, I'm not sure what temp is normal? also the sea temp is pretty cool right now, i imagine in the summer when its 10 deg. warmer it might run hotter.
 
195 F is 90 deg C (sorry I think in Celsius). Most marine diesels I have dealt with.including some Volvos, seem to run more in the 80 - 85C range or closer to 180F. Some however do run up around 195F but I think you probably still have an issue of some sort and probably don't want it running hotter when you get warmer water temps. Personally I am 'paranoid' about temps on my engines. They run right on 82C at cruise and go up to maybe 87C at WOT. When we go away on a long range trip and I have the boat loaded up with people, gear, fuel etc for 10 days (so really heavy) I decide what speed I will cruise at by watching my engine temps. Once they start climbing above 82C I throttle back until they sit on 82 again and that is my cruise speed until I burn off some weight. In summer that normally means dropping back from 19 - 20knts to 16.5 - 17knts. As we burn off food and fuel etc over the trip I can increase my cruise speed and hold the 82C temps. In winter I don't need to drop speed quite as much. So far I have put 4500 hours on this pair of engines in the past 15 years and have only spent $200 on a sender unit outside my routine maintenance. The other habit I have is to always 'warm down' the engines after use. Let them idle and don't turn them off until you see the temps drop back by maybe 5 - 10 deg. That means that the internal hot spots that occur inside the engine when you are making power have time to equalise and this reduces the cooling stresses inside the engine. High temp fluctuations are an engine killer so I would keep hunting for what is going on in your engine. Is there any chance that some old broken impeller pieces might be stuck in the cooling system somewhere?
 
You know I may have some old barnacles stuck inside the sea water side of the through the hull valve. I neglected to check when painting the bottom this year. There was no missing pieces from the impeller but just about to break off, glad I caught it in time. I hope i can pull the hose off the valve from the inside and check rather than going diving under the boat.
 
If you can get a bit of hose on the valve so the top of it is above the waterline you can clean the thruhull from the inside unless there is a hard bend somewhere to get around..
 
Well, checked the thru hull raw water fitting and it was clean free of debris. Also checked both thermostats and are both opening at 180 and fully open at 185 deg. Also had someone drive the boat at cruising speed while I checked the strainer water flow, and was not being starved at all. I don'e know what else to check?? Any ideas
 
Here is the normal overheat check list I use to make sure everything has been checked (in no particular order)"
1) Dirty hull or props
2) Damaged props
3) Air leak in raw water pump pickup system
4) Raw water pump impeller
5) Raw water pump end plates or cam wear
6) Blocked Heat Exchanger
7) Blocked after cooler
8) Blocked oil cooler or transmission cooler if fitted
9) Blocked exhaust elbow
10) Blocked or obstructed intake
11) Blocked strainer
12) Bad coolant pump or slipping pump belts
13) Bad thermostat

These all assume that there is no coolant loss or water leaks around the engine

So what hasn't been checked yet? Any belt dust to suggest a possible slipping belt? Maybe try marking the belt and pulley at one point where they meet and then run the engine up under load to see if the marks have moved apart? Have you tried running with the thermostat out?
 
Well I tightened the belts before launch and no belt dust to speak of. I wonder if one or both hubs on the props may be slipping? How would that make the engine overheat? I will mark the pulleys and see if they may be slipping. One thing i hadn't mentioned is that I am not getting full RPMS at top speed. I should top out at 3900 and only making 3600. Also if I run with the stats out will the engine ever come up to normal temp, ie; too much cold water all at once.
 
Running out of new ideas now. How long have the props been in the water and how are they protected from fouling? The low WOT rpm's can obviously indicate an overload which can lead to an overheat. No chance that the props are damaged or are somehow a size to big? If the props are all good then next best check would be boost pressures. I guess another possibility would be some form of restriction in the exhaust. That would probably reduce the turbo boost and could also lead to hot running. Hard to imagine how that could happen though.
What rpms do you cruise at when you are seeing the 195deg temps?
Your engine is supercharged and turbocharged correct? What rpm's is the supercharger cutting out at, and does it transition straight to the turbo or can it 'hesitate' a bit before transitioning?
 
Well the props do not have any growth on them since its just launched less than a month ago. If i use the boat a couple times a week it doesn't grow. If there is growth i scrub from swim platform. The boat was originally sold to me, new with the wrong size props and within two weeks the manuf. replaced with the correct size. I am supposed to turn 3900 RPMS at top speed with all gear and full tanks with 4 people on board and never had a problem doing so since the correct props were installed. I am getting ready to call a well known diesel mech. to put a boost gauge on to see where and if i am loosing pressure somehow, i do not have a boost gauge or i could do it. Do you have any suggestions on where i position the gauge and at what speed to take measurements if i got a hold of a gauge. I cruise at 3000 RPMS for about 7 mins and it is just starting to peak close to 200 deg. My supercharger kicks in at 1400 and turbo kicks in at around 2800 RPMS, no hesitation.
 
If there is no lag between the supercharger and turbo then your boost is possibly OK. Normally the first sign of a turbo boost issue is an oscillating handover from supercharger to turbo. You won't know for sure though without checking.
Trying to think what could cause you to lose power (top end rpms) and also run hot. Could be a coincidence but probably not. If there is no overload condition with everything clean, which it seems not, then the things to consider are - boost, injectors, aftercooler, injector pump, compression, air cleaner, exhaust flow. You have recently cleaned the aftercooler, and the air cleaner. Low compression probably won't make you run hot. Low boost probably won't make you run hot. Maybe a leaky injector and overfueling might, but I don't think that is normal. Thought - could your injector pump timing have slipped? Would be pretty unusual but another check if you have a diesel guy visiting.
That's all I can think of at the moment.
 
Today I measured the coolant capacity and it was well above -45 which is way out of the norm of 50/50 mix. This could be my temp problem, does'nt the coolant act as an insulator if you have too much coolant to water mix. Also as i said earlier that i cleaned the inner cooler last season then after the fact the exhaust leak that i since took care of. Never realizing that the inner cooler got gunked up again that quick with the exhaust leak. So I cleaned the element again which was really dirty again and drained 1.5 gals of coolant out of the system and replaced with water. I didn't have time to test today but tomorrow I will, I'll bet that i will have different temp readings, ( hopefully ). If not, back to the drawing board and will start taking boost readings. Hopefully I don't have to get the Diesel guy involved, I know how expensive it can be. I will follow up on my results after testing.
Thanks once again for your expert knowledge.
 
I don't know too much about coolant as I seldom have an issue with it but yes the coolant transfers less heat than the water. The coolant to water ratio can also be varied depending on how cold you get in winter I think. In general more water gives better cooling. Whether that will correct the problem on it's own I am unsure. If your intercooler is also a but dirty and blocked though, that could add to the overheating to some extent and of course contribute to the loss of RPM's. Not sure that either of those or the combination will be your final solution but get them right and see what improvements you can get.
 
Did a flush on fresh water system with a little drop in temp. Then did a descaling on my raw water side with a heavy duty inhibitor and let stand for 3 hours. After reclaiming and testing i now am running at about 185 deg.or so, note this is without glycol back in the fresh water system. Will add tomorrow and see if i am still running cool.
 
Back
Top