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White smoke from exhaust

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wet_wonder

Contributing Member
"I have a 5 cyl V8 single inbo

"I have a 5 cyl V8 single inboard setup - I believe it's a Mercruiser 302 or the like - and I have white emission smoke at any rpm above 1000.

The temp gauge will hit 180 degrees when I'm at about 1,200 RPMs. As the RPMs increase over 1,200, the temp will keep rising and the white smoke will increase. At 2,500 rpms, the temp will climb to 220, white smoke continuing. Water sputters out the exhaust, along with the white steam. I can't really tell if it is a proper flow, even though all these clues suggest it isn't.

I have a raw water system. So as not to be mistaken, the water taken in from the seacock directly cools the engine before exiting via the risers.

I bought the boat - Trojan Express, 25', 1976 - last year and inherited this condition. This off season I replaced the thermostat and impeller. This season the smoking/over heating continues. Otherwise, the engine and all other systems perform very well. The motor was installed in 2005, and has 280 hours on it.

I figure that there is probably a circulation problems, via a blockage, etc., and that I'll need to take the screen off, the hoses apart, the risers off, and the manifold off to inspect the exhaust system. And will find clogging. And I'll need to clean everything out, and replace some of it, as needed.

That said, I'd be grateful for any insight my fellow boaters may have before beginning this project, which will sideline the boat for a couple of weeks.

Thanks very much,
Wet Wonder"
 
"Sounds like maybe a head gask

"Sounds like maybe a head gasket problem. Perform a compression test, dry and then wet w/a tablespoon of engine oil. Post your findings. Look at the spark plugs while out. They should be med. brown to tan in color. If one or two are clean it may be a little water entering the cylinder when hot. Black and dry is rich and black and oily is a bad valve seal or rings. Worst scenario is a cracked head or block."
 
"You mean a 5 Litre V8? You sh

"You mean a 5 Litre V8? You should take your hose off that goes into your circulating pump on the front of the engine and do a flow test. With the hose off, get a mop bucket or so and start the engine with the hose in the bucket, see how long it takes to fill the bucket. It should be about 30 seconds or so. If it takes a minute or longer, you don't have enough water flow. You could try backflushing the system, there could be chuncks of old impeller stuck in the system, remove the T-stat housing and check for excess rust. Start with that stuff and see how you make out."
 
"You mean a 5 Litre V8? You sh

"You mean a 5 Litre V8? You should take your hose off that goes into your circulating pump on the front of the engine and do a flow test. With the hose off, get a mop bucket or so and start the engine with the hose in the bucket, see how long it takes to fill the bucket. It should be about 30 seconds or so. If it takes a minute or longer, you don't have enough water flow. You could try backflushing the system, there could be chuncks of old impeller stuck in the system, remove the T-stat housing and check for excess rust. Start with that stuff and see how you make out."
 
"Thanks Jeff, I'll try the

"Thanks Jeff, I'll try the flow test first before taking any more substantial steps.

Gary, I was leaning away from the head gasket angle b/c of the overheating problem. I didn't think the two necessarily go together. What do you think?"
 
Dave:

"This off season

Dave:

"This off season I replaced the thermostat and impeller. This season the smoking/over heating continues."

That statement lead me to the head gasket thought. Compression test won't hurt and can tell you alot. Use a laser thermal temp. gun to check temps. around the engine. Let's hope it's a chunk of debris in the water inlet hose at the oil cooler.
 
"Dave...

The first thing I

"Dave...

The first thing I thought of was head gasket as well. White smoke from the exhaust is very often cooling water of some sort being burned during combustion. A bad head gasket can absolutely contribute to engine overheating. A cyl leak down test, or simply pressurizing the cyls with an external source of compressed air will show this. Be sure that the smoke really is white as you say and not having a hint of blue in it. This blue would indicate oil burning. At all rpm's indicates bad rings. If only at acceleration after a period of idleing would indicate bad valve guides. Oil consupmtion will not contribute to overheating, unless of course you run it completely out of oil and the thing is about to sieze. ( I trust that this is not the case).

Wrench"
 
"Thanks Wrench. The white ste

"Thanks Wrench. The white steam definitely has no blue in it, and I have no oil depletion.

So it sounds like you'all are leaning towards the head gasket rather than the exhaust system. I tend to think it isn't the rings, being that the motor is fairly new. Head gaskets are easy enough to replace - easier, in my opinion, than ripping apart and cleaning the entire exhaust system.

I'd welcome any other confirmations or thoughts. Thanks, Dave"
 
"suggest you run a pressure te

"suggest you run a pressure test on the block cooling system. If it does not hold pressure, then you have a leaking gasket, cracked heads or block.

Also, jeff's advice to test the water flow into a bucket is good, but I think he means to remove the hose that brings cooling water from the drive at the stat housing and test the flow there into a bucket. That will tell you if you have sufficient cooling water flow.

Another thing is to get an IR temp gun and check your exhaust manifold and riser temps. Manifolds should be up to about 190, and the riser/elbows should be no more than 120 or so. If you can't hold your hand on the risers, you have insufficient water flow.

Rod"
 
"Rod, Do you know of a link th

"Rod, Do you know of a link that instructs on how to pressure test the cooling system as you advised?
Thanks,
Dave"
 
"No, but you need to block all

"No, but you need to block all the exits, then attach a fitting with a guage and a Shrader valve. Pretty easy to rig up.

Disconnect each hose to the exhaust manifolds and risers and plug them. A chunk of dowel and a hose clamp works well. Wine corks are also good.

Btw, you only need about 10-15 psig.

Rod"
 
"In terms of the temp gun test

"In terms of the temp gun tests on the manifolds and risers - if this test does show too much heat there, indicating insufficient water flow, does that then exclude a pressure leak? - And turn the focus to blocked circulation?"
 
"High Temp in the exh manifold

"High Temp in the exh manifolds/risers does not exclude head gasket from the list of suspects.

Consider that when huge pressures from the combustion chamber starts "burping" into the water jacket, that burped gas displaces water, and raises the pressure in the cooling system. While eventually that pressure will find its way out through the risers, it will be as a gas, not the water that you want to pump through the risers to cool them and the engine...and oh by the way, that extra pressure is pressure your impellor has to work against to try to pump water INTO the system, so you can have hot temps on gauge and exh manifolds/risers from either a flow restriction or blown head gasket.

Guy had some good advice for you earlier in the string when he said check plugs. Plugs usually tell all re a head gasket.

Water in a combustion chamber is an amazing cleaner. Take a little time and check your plugs. If one or two clean ones don't pop out, you can PROBABLY rule out a head gasket. At that point, after ruling out a head gasket it makes alot of sense to move on to some of the other more involved tests that learned folks here have suggested.

Just my 1.5 cents worth..."
 
"Many thanks to all of you.

"Many thanks to all of you.

Tomorrow I will (1) pull and check the plugs, and (2) run raw water from the hose off the thermostat housing into a bucket. Those two tests seem, from everyone's input, to be the easiest way to assess the head gasket and water circulation. Thanks again very much and I'll report back with my findings."
 
I was going to suggest pulling

I was going to suggest pulling the plugs to find water on any of them. I had a ported small block chevy that did the same thing........the head cracked between the exhaust and intake valve....
 
"I couldn't be happier tha

"I couldn't be happier than right now. I went to run a waterflow test into a bucket and to check the plugs. The first thing I did was to run through the cooling system hose network to get familiar with it. The seacock is in a difficult position, at the front of the motor and right under the fuel pump. From the seacock valve, the first hose runs under the motor to the other side of the front, ending at the water pump input. I ran my hand under the motor and along the hose and felt what seemed to be a very large whole. I pulled the hose, and here it is. The outer lining is torn through and the inner lining crushed inward, reducing the opening to almost nothing. They damage you see here is not a result of me pulling it out - this was actually how it was when I ran it last weekend from Philadelphia to Cape May and back. Hopefully, the smoke and overheating problem starts and ends with this hose damage. I'll install a new section this weekend and find out. (Incidentally, can I get a replacement hose from an auto parts store, or is there more to it?)

Thanks for everyone's help, Dave

217085.jpg
"
 
"Great! If it looks like a mo

"Great! If it looks like a molded hose then I would replace it w/the same type. If just a heater type hose any autoparts store can sell you a replacement length. If the damage to it came from rubbing against the hull or other, purchase a black plastic wireloom sleeve for that location of the hose."
 
"YIKES!
So that is the water

"YIKES!
So that is the water pump suction hose, right?

There is a type of heavy wall stiff braided hose generally used for the sucttion hose that is intended to prevent suction damage such as that.
Not sure its type number, but you should be able to get it at any marina or marine dealer.
The one that came on my 6.2 from the factory was a pink color, it may be a silcone elastomer.

That one looks like its deteriorated from sitting in oily bilge water. It may not have been marine rated I am guessing.

Rod"
 
"Thanks for that tip. It does

"Thanks for that tip. It does look like the damage was caused by suction. I will check Westmarine and see what they have. If anyone knows specifically where to get the proper hose, please LMK. Thanks."
 
"The suction piece will not be

"The suction piece will not be a pre-formed piece, as it is field run by each boat builder to suit the installation. It will be stock hose sold by the foot.

Rod"
 
"After I installed the new hos

"After I installed the new hose, I learned that the damaged hose tore up the intake impeller. So I pulled the pump, and the impeller was so chewed I couldn't tell what direction to install the new impeller. I believe the pump turns clockwise when looking into the impeller housing - so are the curve of the blades to face away from the clockwise direction, like the bend of a broom when you're sweeping it forward? (See photo below.) I figured that was the orientation, but I just wanted to confirm.

217180.jpg
impeller direction
 
"If the engine is a standard R

"If the engine is a standard Rh rotation, the pump will turn Cw from the front. Confirm by checking the belts, as with serpentine belts some acessories rotate the other direction.

Then the blades sweep back CCw as you have noted.

Rod"
 
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