Low compression, high temp.

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First time caller. Mercruiser 6.2, serial number 1A314659. Bravo 1. Sea Core if it makes any difference. Closed cool system. I have two separate issues at this time. The raw water pump seal was leaking, installed a new pump and took it for a test run. The boat ran good but I noticed a significant decrease in fuel economy. In the past I was getting 2.5 maybe 2.6 mpg, now I struggle to get 2.1 mpg. I flushed the engine and parked the boat for a few weeks. The next time I went to crank the boat it hydrolocked. At that time I pulled off the exhaust elbows and they were definitely shot. There was water in the exhaust manifold. I pulled the spark plugs and spun the motor. Then installed new elbows and the boat ran pretty good. But now it's slightly overheats, instead of 160°, it is running around 172° at 4,000 RPMs, but comes back down to 160° at idle. Did not know if this was early symptoms of bravoitis.
Installed new spark plugs, cap, rotor, wires. Drained all of the fuel, clean the fuel tanks, and installed a new Cool Fuel with all new guts. Next test run the boat ran the same. It runs pretty good but still lower fuel economy. Did a compression test on all eight cylinders. 175 PSI on all cylinders except number 1 and number 3. Number one had 145 PSI and number three had 140 PSI. Performed a leak down test and both cylinders had about a 10% leak down. Could not tell, other than going back into the crankcase, where the air was going. Could not hear anything in the intake system or exhaust system, and no bubbles in the coolant. It did not seem to be leaking from cylinder to cylinder either. Purchased a borescope and could not see anything wrong in the two cylinders, but it is hard to tell. Did a wet compression test and cylinder 1 came up to 175 PSI, and number 3 stayed below 150 PSI.
My questions are can bravoitis come on slow and only have an effect when I am under a load. Also will these two cylinders with lower compression affect fuel economy that much. What are the thoughts on maybe stuck rings or broken rings?

 

[Dieter]

First time caller. Mercruiser 6.2, serial number 1A314659. Bravo 1. Sea Core if it makes any difference. Closed cool system. I have two separate issues at this time. The raw water pump seal was leaking, installed a new pump and took it for a test run. The boat ran good but I noticed a significant decrease in fuel economy. In the past I was getting 2.5 maybe 2.6 mpg, now I struggle to get 2.1 mpg. I flushed the engine and parked the boat for a few weeks. The next time I went to crank the boat it hydrolocked. At that time I pulled off the exhaust elbows and they were definitely shot. There was water in the exhaust manifold. I pulled the spark plugs and spun the motor. Then installed new elbows and the boat ran pretty good. But now it's slightly overheats, instead of 160°, it is running around 172° at 4,000 RPMs, but comes back down to 160° at idle. Did not know if this was early symptoms of bravoitis.
Installed new spark plugs, cap, rotor, wires. Drained all of the fuel, clean the fuel tanks, and installed a new Cool Fuel with all new guts. Next test run the boat ran the same. It runs pretty good but still lower fuel economy. Did a compression test on all eight cylinders. 175 PSI on all cylinders except number 1 and number 3. Number one had 145 PSI and number three had 140 PSI. Performed a leak down test and both cylinders had about a 10% leak down. Could not tell, other than going back into the crankcase, where the air was going. Could not hear anything in the intake system or exhaust system, and no bubbles in the coolant. It did not seem to be leaking from cylinder to cylinder either. Purchased a borescope and could not see anything wrong in the two cylinders, but it is hard to tell. Did a wet compression test and cylinder 1 came up to 175 PSI, and number 3 stayed below 150 PSI.
My questions are can bravoitis come on slow and only have an effect when I am under a load. Also will these two cylinders with lower compression affect fuel economy that much. What are the thoughts on maybe stuck rings or broken rings?

Could be bravoitis or when was the pump impeller last replaced? Did you replace the manifolds as well as elbows? Assuming from your comments it is a salt water boat? manifolds may be clogged and leading to over heat.

As far as fuel consumption have you had the injectors checked ? measured the fuel pressure ? Would think these two things would influence fuel economy not 10% leak down. I would have expected valves hanging up but if you don't get leakage out intake or exhaust , could try decarbonizing the rings with power tune sea foam or GM top engine cleaner. might improve. Possible if the injectors are leaking you have fuel wash in those cylinders

You might check your gauge as well as new these engines were 150 psi so the 175 is probably lower and thus the 140 is lower too.

 

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Could be bravoitis or when was the pump impeller last replaced? Did you replace the manifolds as well as elbows? Assuming from your comments it is a salt water boat? manifolds may be clogged and leading to over heat.

As far as fuel consumption have you had the injectors checked ? measured the fuel pressure ? Would think these two things would influence fuel economy not 10% leak down. I would have expected valves hanging up but if you don't get leakage out intake or exhaust , could try decarbonizing the rings with power tune sea foam or GM top engine cleaner. might improve. Possible if the injectors are leaking you have fuel wash in those cylinders

You might check your gauge as well as new these engines were 150 psi so the 175 is probably lower and thus the 140 is lower too.

Thanks for the reply. Yes I thought the compression reading was a little high. But it was consistent so I went with it. Injectors are new. I did check the fuel pressure it was in specs, don't remember what it is, I do not have my notes with me. However I did also put new fuel pumps in it.

 

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Thanks for the reply. Yes I thought the compression reading was a little high. But it was consistent so I went with it. Injectors are new. I did check the fuel pressure it was in specs, don't remember what it is, I do not have my notes with me. However I did also put new fuel pumps in it

Thanks for the reply. Yes I thought the compression reading was a little high. But it was consistent so I went with it. Injectors are new. I did check the fuel pressure it was in specs, don't remember what it is, I do not have my notes with me. However I did also put new fuel pumps in it.

Somehow I missed the first part of your reply. The water pump and impeller are new. I shouldn't assume but I think the manifolds are fine since they are full of antifreeze and they are only a few years old.

 

[Dieter]

Somehow I missed the first part of your reply. The water pump and impeller are new. I shouldn't assume but I think the manifolds are fine since they are full of antifreeze and they are only a few years old.

Sounds like you have replaced a lot. If you have a full closed system then use safe bet that manifolds are not clogged.

Would look at debris in oil coolers that maybe between transom and pump, barvoitis, kink or crack in hose up from drive. You could put a short section of clear hose in supply line to see if you get bubbles at speed indicative of sucking air in.

Bravoitis seems pretty common issue. for some folks it is easier to install a thru hull than fix depends on how much boat is in the way...

 

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Sounds like you have replaced a lot. If you have a full closed system then use safe bet that manifolds are not clogged.

Would look at debris in oil coolers that maybe between transom and pump, barvoitis, kink or crack in hose up from drive. You could put a short section of clear hose in supply line to see if you get bubbles at speed indicative of sucking air in.

Bravoitis seems pretty common issue. for some folks it is easier to install a thru hull than fix depends on how much boat is in the way...

Thanks. There is a lot of boat in the way. However the motor is coming out soon to address the low compression issue, I'll check bravoitis at that time.

 

[Dieter]

Thanks. There is a lot of boat in the way. However the motor is coming out soon to address the low compression issue, I'll check bravoitis at that time.

that is the ideal time to address this. It fits that if the water intake were restricted that at idle temps can hold, but at speed/under load water flow is impeded. Did you clean your heat exchanger/ take ends off and rod it out?

 

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that is the ideal time to address this. It fits that if the water intake were restricted that at idle temps can hold, but at speed/under load water flow is impeded. Did you clean your heat exchanger/ take ends off and rod it out?

That's a good idea. I should do that. I did not have any kind of issue with my impeller though. It did not come apart and get into the system. But corrosion could be an issue. Once I pull the motor and figure out what's going on and fix all the issues I'm going to make a good post about what I had to do to cure my problem. One of the things that bothers me about researching and reading some of these forums is several OP's do not come back and state how they fixed their problem. I wish I had more knowledge to contribute to the forum to help but maybe that will come after I get my boat fixed.

 

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Finally got things in order. I pulled the motor and definitely had bravoitis. New hose installed. Runs at 160 degrees now.
It seems the low compression issue was stuck piston rings. I had the motor out for over a month. Addressed other minor problems. Painted the bilge and did a thorough cleaning. While the engine was on legs, cylinders were treated with seafoam and MMO while rotating crank daily. Fuel economy is back up to 2.5 MPG. Things seems pretty stable after 20 hours of runtime.