Extreme Heat at Exhaust Elbow Universal 5432

[Westy2]

I have a Universal (Kubota) 5432 that runs well and seems to operating well with one exception.

The issue: when under power at anything over 1700 rpm the exhaust elbow gets so hot it starts to smell terribly and at one point it got hot enough to cause the muffler/header wrap to smolder and smoke. It was scary hot so I backed down and motored at low rpm and the heat dissipated. The high heat condition occurs when the thermostat is in the 160 range so there is no way the kubota can get close to ideal operating temp and it does not appear to be over-heating. Maybe the sensor is not catching the overheat condition due to location and it is heat transfer or flow in HX.

I have not replaced the heat exchanger (it is 3" sen-dure) but put on new end caps and zinc (zinc was gone); pumped out muffler in the event of build-up and sucked all hoses out with shop vac in the event of blockage and/or back pressure. I have not pulled elbow off the manifold and cleaned out but the RW entry connection is clear.

Anyone ever have this condition? Thanks for any input.

[Dockhead]

The only possible cause for this is lack of raw water flow into the exhaust elbow.

The exhaust elbow normal condition is stone cold, as it is supposed to have the entire raw water flow of the engine flowing through it.

Note that this has nothing to do with the coolant flow in the engine or the thermostat. The exhaust elbow is the end of the road for the raw water -- it is picked up from your sea water strainer by the raw water pump, is pumped through your heat exhanger, might also be pumped through an oil cooler, intercooler, or other odd bits, but after it's been through those places, it is dumped out into the exhaust via the exhaust elbow, where it cools the exhaust gasses to the extent that the exhaust gasses can be handled by rubber hoses and plastic mufflers.

So you should go through the raw water system and find the blockage -- it is blocked somewhere. A greatly reduced flow of raw water might still be enough to cool the heat exchanger, but not enough to cool the exhaust.

Have you checked your impeller and raw water pump?

[Westy2]

Thanks for the quick response Dockhead and agree. Understand, on the separate circuits and relationship of stat and raw water. I have not done a bucket test to see GPM flow of raw water pump at exhaust outlet and that is on my list. I have a new Moyer MM502 pump with basically Oberdorfer flow rate characteristics so I now it is moving water but maybe it is hitting resistance.

Interestingly, the entry point of raw water into my exhaust system is after the elbow. The elbow looks to be steel pipe off the manifold that drops into muffler can. Have looked at lift, etc. Also, no oil and/or intercoolers in circuit. If it is flow it has to be in HX. I can tell you that the exit water in the exhaust stream is warm and picking up heat.

Thanks much

[Dockhead]

Originally Posted by Westy2

Thanks for the quick response Dockhead and agree. Understand, on the separate circuits and relationship of stat and raw water. I have not done a bucket test to see GPM flow of raw water pump at exhaust outlet and that is on my list. I have a new Moyer MM502 pump with basically Oberdorfer flow rate characteristics so I now it is moving water but maybe it is hitting resistance.

Interestingly, the entry point of raw water into my exhaust system is after the elbow. The elbow looks to be steel pipe off the manifold that drops into muffler can. Have looked at lift, etc. Also, no oil and/or intercoolers in circuit. If it is flow it has to be in HX. I can tell you that the exit water in the exhaust stream is warm and picking up heat.

Thanks much

I have never seen an exhaust elbow without a raw water injection point. Are you sure it's supposed to be like that?

It is normal for the exhaust to be hot ahead of the raw water injection point, so you can forget everything I wrote before.

Exhaust gas temperature depends on how much fuel is being injected and how much power is being produced, not on the temperature of the fresh water coolant or the engine itself. So a cold engine can produce hot exhaust if enough power is being produced (not necessarily a good idea).

[Westy2]

Thanks for the clarification on entry point of Raw Water into exhaust and your path down the road of fuel, timing, etc. is where I am currently going. So could:

1. The fuel problem causing carry over and ignition after the combustion cycle in the exhaust (i.e.heat)?
2. Could it be timing?
3. Could the raw water flow be to weak to carry the heat out of the maniflold/riser/elbow?

I am trying to avoid getting into injectors, timing, etc. but am running out of variables. Only one left is the Sen-Dure HX. Unfortunately, when I cleaned up and put end caps on I did not acid clean. It looks to be original (1983) and maybe she is shot.

Toughy for sure. Thanks again for insight.

[Dockhead]

Originally Posted by Westy2

Thanks for the clarification on entry point of Raw Water into exhaust and your path down the road of fuel, timing, etc. is where I am currently going. So could:

1. The fuel problem causing carry over and ignition after the combustion cycle in the exhaust (i.e.heat)?
2. Could it be timing?
3. Could the raw water flow be to weak to carry the heat out of the maniflold/riser/elbow?

I am trying to avoid getting into injectors, timing, etc. but am running out of variables. Only one left is the Sen-Dure HX. Unfortunately, when I cleaned up and put end caps on I did not acid clean. It looks to be original (1983) and maybe she is shot.

Toughy for sure. Thanks again for insight.

There are many on here who know vastly more than I do about Diesel engines, so maybe we should wait for them.

However, I do know a tiny bit -- Diesel engines, unlike petrol engines, do not have such a thing as "mixture" and so won't develop high exhaust gas temperature because of lean mixture like petrol engines will. On the contrary, the less fuel injected, the cooler the exhaust gasses. Abnormally high exhaust gas temps, caused by something other than overloading the engine, are, as far as I know, pretty rare. Mostly caused, if I am not mistaken, by combustion occurring outside of the cylinders, like in the case of very delayed injection timing, dribbling injectors, etc. If the engine is running normally then this just about can't be your problem, I think.

Yes, if raw water flow is weak and is not cooling the manifold, then that of course could be the problem. It would mean the manifold is getting abnormally hot and the heat leaks into the elbow. But I would think you would get some boiling of raw water around the manifold and steam -- do you see any steam in the exhaust?

Do you have a turbo?

[Westy2]

Great thought on fuel. The thing runs well, no excessive fuel burn, etc....no Turbo and yes steam (I thought was white smoke)..I noticed this prior to ending up at the elbow..now it is all coming together. It's got to be flow at elbow..off HX.

New thought; I did notice that when I replaced the hose from the HX out to the exhaust inlet hose it goes to a vented fitting a the highest point on the bulkhead in the engine room. For siphon issues I read. BUT, the hose from the HX is 7/8 and this fitting with vent line is clearly smaller (fitting the hose on barb was tough. The path is from HX to top of loop and this fitting and then it dumps into exhaust. It looks original but maybe not and could be a flow restriction point before it enters the exhaust elbow.

[Dockhead]

Originally Posted by Westy2

Great thought on fuel. The thing runs well, no excessive fuel burn, etc....no Turbo and yes steam (I thought was white smoke)..I noticed this prior to ending up at the elbow..now it is all coming together. It's got to be flow at elbow..off HX.

New thought; I did notice that when I replaced the hose from the HX out to the exhaust inlet hose it goes to a vented fitting a the highest point on the bulkhead in the engine room. For siphon issues I read. BUT, the hose from the HX is 7/8 and this fitting with vent line is clearly smaller (fitting the hose on barb was tough. The path is from HX to top of loop and this fitting and then it dumps into exhaust. It looks original but maybe not and could be a flow restriction point before it enters the exhaust elbow.

Maybe you could post some photos?

Then hopefully some of the more knowledge folks here will chime in.

If your engine ran well and didn't have this problem before, then it's unlikely to be the antisiphon valve. I would put money on a clog somewhere.

Do you have a raw water strainer? All kinds of carp gets sucked into raw water systems, and besides that they are prone to salt deposits. If I were you, I would clean it out from one end to the other and be very sure that there are no clogs or restrictions.

And you have checked to see that you don't have a flow restriction IN the raw water strainer, do you?

This very summer, I noticed that I was getting whiffs of steam out my genset exhaust. I shut it down and found that the sea water strainer was packed with kelp. So the first symptom was inadequate cooling of the exhaust, leading to steam out the exhaust, although the restricted raw water flow was still enough to cool the genset engine itself.

[Westy2]

Thanks Dockhead; Not sure how well it ran before. No raw water strainer but just grate and sea cock. More the reason tho think there may be some heavy junk in HX. Will take your advice on the cleaning and the only thing I have done so far is blown out from inside to clear the intake. Seems OK but hard to tell what may be around grate. I will have to go under and take a look.

Thanks again...stay tuned as my resolve will be posted for other to benefit.