Big difference in exhaust water expelled from risers

[oldOMC]

I've been working on rebuilding a 5.8L OMC Cobra from 93. So far I've gotten almost everything working and have succeeded in starting the engine.

I noticed a new issue with the exhaust water. Water was inserted through the middle inlet coming from the transem. I tried it with both half and full pressure. The starboard side has considerably less water coming through the exhaust riser. Most of the water is coming through the port side. Another observation is that the port riser is keeping much cooler than the starboard. I've replaced the thermostat housing as well as the thermostat. The part came obstructed on one side of the outlet going to the manifold. I had to drill a hole through in order to clear it. As a result it is 1/32 larger. Could this make such a difference? The starboard side also had 2 pistons replaced due to water damage and the manifolds installed weren't replaced brand new but were slightly used.What could cause the difference in the ammount of water coming through each exhaust? If it would have not have been for the engine being out of the boat I wouldn't have been able to observe this.

What could cause the imbalance in exhaust?

I'd really like to get this all right before I place it back in the boat. I appreciate any and all replies as the manual doesn't really address this issue.

 

[Gary H NC]

Re: Engine started! A few more issues =/

Re: Engine started! A few more issues =/

If both manifolds have been checked and known to be good then i would say it could be normal.
Many boats do it and have one side running a little warmer than the other.
Nature of the beast on some applications.

 

[oldOMC]

Re: Big difference in exhaust water expelled from risers

Gary thanks for your reply and and for your suggestion that it could be normal, however it still puzzles me that the discharge should be somewat equal from each exaust. Onthe port side water is flowing while the other side it's like spray mist.
Should I run the engine for 10 or more minutes to see if it equalizes? I am afraid of causing engine trouble, also should i run a compression test to see if the problem is caused by engine compression? ANY ADVISE IS APPRECIATED

 

[JustJason]

Re: Big difference in exhaust water expelled from risers

Gary thanks for your reply and and for your suggestion that it could be normal, however it still puzzles me that the discharge should be somewat equal from each exaust

Because of hose sizes, lengths, and diameters, because of circulation pump direction, because of internal rust and junk, and because water always takes the path of least resistance, 1 manifold will always discharge more than another. The path of less resistance is should be close between the 2 manifolds, but they are never equal. Because of that its common for 1 manifold to be 10-15 degrees hotter than the other.

You need to check the cooling system with the boat in the water, under load. The muffs won't tell you anything. Get an IR pyrometer and take a run around the lake and then shoot the manifolds and risers. Below 160F is good, over 160F you have clogged manifolds/risers or some other cooling system issue.

How'd you ever make out on your voltage drop problem?

 

[Jeepster04]

Re: Big difference in exhaust water expelled from risers

Our 305 volvos are the same except the port side is the one that gets a little warmer. Both engines are the same and I was told on here thats its normal. Ive checked them with an IR gauge and the difference between the two isnt that great. Just as long as the difference isnt major. Theres not been a time that Ive not been able to touch either side though. I cant hold my hand on the port side but its not hot enough to burn me or anything. Cant remember the numbers from the IR but I think it was around 120 or 130 or so at the hotest.

 

[Bondo]

Re: Big difference in exhaust water expelled from risers

What could cause the imbalance in exhaust?

Ayuh,.... As explained by Jason,... You might be chasing a ghost that doesn't exist...
Or,...You have a restriction on 1 side....

 

[oldOMC]

Re: Big difference in exhaust water expelled from risers

Tryed to reply in detail three times but I screwed up. it wont post.

Jason, taking every thing into consideration, I will drill the two nipples goin to the exaust the same size,run and flush engine few times. Maybe I had too much pressure on my garden hose!

Voltage drop test revealed a weak ground cable ,it was replaced and engine started working the choke.

Better post this before it times out//////

One more Question. Should I allign the engine when I put it back in the boat?.It will go back on the same motor mounts. I don't have an allignment tool.

thanks again to all the GOOD PEOPLE on this forum

 

[intrepidvoyager]

Re: Big difference in exhaust water expelled from risers

Hi ......read thru all this and you will know how to check ....there can be slight temp diffs at each riser but as an example on our big block Rinker you can hold your hand on the riser for 10 secs ..no problem ..... pressure is distributed equally in all directions .... so you should not have a significant diff .... so you can see from one riser discharge to the other .... also check that the exhaust Y flappers are not restricting flow.Originally Posted by intrepidvoyager

For example the circulating pump on a standard small V8 GM based engine will flow approximately 50 gpm through the engine. The typical raw water supply pump is capable of flowing about 18 - 20 gpm depending on the gear ratio and restriction the system experiences. A standard 300 Hp small V8 engine dissipates approximately 300,000 Btu/Hr of heat into the coolant. To maintain a thermostat temperature of 160 degree F at wide open throttle this engine would need a pump to flow about 8 gallons per minute (GPM) of 70 degree F water into the system to maintain this engine temperature. Since the Alpha raw water pump can flow 18-20 GPM there is significant bypass (excess) water supplied, which therefore has to be dis-charged somewhere.

In a cold manifold system the warm water that flows through the thermostat, as well as this excess bypass water are joined together in the thermostat before exiting and being introduced into the bottom of the exhaust manifold. The fact that your are mixing together a lesser amount of 160 degree F engine water (8 GPM) with 10+ GPM of cold lake water allows the aggregate coolant temperature in the manifold to fall below the 110 degree F threshold needed to prevent the accumulation of condensation in the exhaust system.





only problem is this is a bit hard to test without the leg actually in water .....in your case you need a non pressurized supply to the raw water pump .. you cannot take the chance of getting water in the engine by running hose water, engine off, thru the manifolds to see if there is a blockage in the manifold/riser ...... if you can get the leg in a big bin fed by a hose that would be great ........ watch that the water level in the bin does not get too low as your raw water pump can pull up to 18 gallons a minute . ..

STEP ONE ..... start the engine and let it run up to thermo temp ...now check both hoses running from the thermo to the manifolds ..... if they are hard and cannot be squeezed at all you have a blockage in your manifold/risers or the manifold/riser gaskets are wrong or improperly installed.

Also check that there are no bits of old impellor blocking the hose at the manifold cooling water inlet on the bottom of the manifold.

If the hoses can be squeezed ..... there is water flowing thru them but should not be under a lot of pressure .... OK turn the engine off .. if this test is ok .....then go to step 2

STEP TWO

...... now you know what 18 gallons looks like ....if not measure it out .... ok put a piece(s) of ply over most of the bin so exhaust water does not go back in the bin ........ take the hose feeding water out of the bin .... now start the engine at zero seconds on your watch and keep an eye on the water level in the bin ......... so the idea is to see how much water your pump is pulling ....in 30 seconds should be around 9-10 gallons ......if its less than that you got a raw water pump issue or some blockage in the raw water line/ps cooler/thermo housing

good luck ....let us know

 

[Bondo]

Re: Big difference in exhaust water expelled from risers

One more Question. Should I allign the engine when I put it back in the boat?.It will go back on the same motor mounts. I don't have an allignment tool.

Ayuh,... Alignment is a MUST for any motor pulled,+ reinstalled...

 

[intrepidvoyager]

Re: Big difference in exhaust water expelled from risers

hold the phone ...Have you checked the raw water pump/impellor......did you check your raw water hose/cooler for debris ? ....also now easy if not already done to pull the riser hoses and check for impellor debris, etc. WATER OK ON ONE SIDE AND MIST ON THE OTHER IS BAD NEWS !!!! ..... also check the Y exahust tube for stuck flappers BEFORE you put the engine back in.

RE ALIGNMENT TOOL ..... they only cost $60 so you should be able to rent one from a boat yard ..... around here its $30 for the weekend.

If your raw water pump is functioning properly you definitly have a blockage on one side .....either thermo or hose to manifold/riser or in manifold/riser itself. Anyway previous tests i sent will enable you to find exactly where you have a problem. Good luck .....

 

[intrepidvoyager]

Re: Big difference in exhaust water expelled from risers

re-read your original post and biz about drilling ..... if you are using the same manifold riser set up that caused the original water in engine problem ..GET RID OF THEM ..... you can potentially clear up this problem but 6 months from now you could be doing the same rebuild all over again. Old manifolds/risers can pressure test fine one day .... then in 3 months they are leaking like a sieve.

Mercruiser pro mecs says risers every 3 years and manifolds 5 ( unless hp alu )

if you can start the engine again out of the boat check the hardness of the hoses going to the manifold/risers ..you should be able to squeeze them with your hand ...if either is hard ....cannot be squeezed .....you got a manifold riser blockage. Normally this test is boat in water at 2000 RPM ....... so if they are rock hard at idle RPM you have a major blockage issue.

 

[oldOMC]

Re: Big difference in exhaust water expelled from risers

Intrepid- I want to thank you for all your input and knowledge in this area. I have not been able to try your suggestions yet but if the weather clears tomorrow I will be making some noise.
The manifolds and risers that I Installed now were bought slitely used from a marine who said that they were pressure tested, they look ok.
Will update you guys soon.

 

[oldOMC]

Re: Big difference in exhaust water expelled from risers

Today I have tried to run some tests as intrepid suggested to see how much water it woud take and time it, but it didn't work. It wasn't pulling the water from a tank so I had to reattach a garden hose with limited pressure.
-drilled same diameter hole on each nipple
-leveled the engine (water will flow towerd lowest spot)
-Gave just enough water pressure not to bypass the thermostat
-Kept engine running for 15 min
Observations:
Water volume was still greater on the port side but not as much as before
Port side elbow was cooler due to the more flow of water but still warm enough. Both Hoses were flexible when squeesed.
Starbord side was throwing more smoke especially when accelarating (that is the side that had two pistons replaced and the cylinders honed with a tool)
I think I should accept it for what it is. AS many suggested on this thread
it's the nature of the beast! as log as water is circulating.
For an amature I am happy with the results of this rebuilt, few mechanics did not even consider using the same block.
Next I will do a copression test to be on the safe side and align the engine as it was recommended here. (Ordered the Tools)Thank you all!

 

[intrepidvoyager]

Re: Big difference in exhaust water expelled from risers

Ya ...all sounds good .....but the fact that your pump could not draw from a bin indicates ...if level of the water was high enough relative to the pump , then sounds like you got an air leak somewhere before the pump or the pump itself .....you can test if you like by installing a clear hose temporarily at the end of the pump line and look for air bubbles ....OR .....oops got to run ...I'll get back to you ...

 

[oldOMC]

Re: Big difference in exhaust water expelled from risers

You're correct! I didn't raise the water bin HIGH enough in relation to the pump.I assumed it would have some suction. I still have a lot to learn!!!!
Thanks

 

[josh5058]

Re: Big difference in exhaust water expelled from risers

Replacing the impeller would save abunch of money,time,headache. Compression and new pistons have nothing to do with how much water flows through the motor.

 

[intrepidvoyager]

Re: Big difference in exhaust water expelled from risers

OK .....re the raw water pump ......these pumps operate at low speed as a displacement style pump ...... thats when the impellor fins are in contact with the housing ..... at higher speeds they take on the attributes of a circulation pump in that the impellor fins move slightly away from the housing bore ....the impellor is actually a precise pice of engineering which when in good condition will maintain the proper pressure in your cooling system at both idle and high speed...HOWEVER ..... if the impellor is old ....even if it looks ok , it may have lost fin stiffness so even at idle speed it is in the semi circulation mode and will not pull water properly. If your engine or riser temps are higher at idle speed (boat in water) than at higher speed thru the water this is a very possible sign that your impellor needs replacing ....... also as mentioned before, air leaks in the pump or water pick up to pump plumbing can severely affect pump efficiency...!.... JOSH said it a bit more suscinctly ...replace the impellor

 

[intrepidvoyager]

Re: Big difference in exhaust water expelled from risers

re SMOKE ....don't worry about it ....just watch your oil level ....honed cylinders eh ? ...well done ... anyway may take a while before the rings take on a set ....if smoke does not lessen after 20 hrs running ....well maybe you have an issue.

don't forget to use normal break-in proceedure .

got a bit wet around here last night

http://images.google.com/imgres?img...s?q=hanalei+flooding&hl=en&safe=off&sa=N&um=1