Overheating 502

[CurrentObsession]

2000 502 Mag MPI Bravo 3 drives with captain call exhaust.

I messed up and didn't notice that I failed to reconnect the hose from the I/O lake water intake hose to the impeller last fall. Launched a few days ago and since it wasn't getting any water I smoked the impeller. Since it was bone dry I found all the impeller pieces right there. I installed a new impeller kit including the housing and verified water flowing by switching exhaust to loud mode so I could see water coming out the back with the exhaust. Took it for a run and 5 minutes in the temp gauge said 220 degrees so I limped back in with other engine. Started it the next day after cooling all night and it is over heating at idle within minutes again and water is coming out the exhaust like it should be. Water spraying out of the back SB side of the engine down low, I can't tell if it's a cracked manifold or where the head meets the block. Oil is not milky so a mechanically inclined friend said that is good news that it might not be a head gasket, but I'm guessing it takes more than a few minutes to get water mixing with the oil to show on the dipstick.

I'm guessing I should start with removing exhaust manifold to see what damage I have done, I'll start that tomorrow.

As for the cause of the overheating, where should I start? T Stat, water pump? What most likely fails when the engine gets no water and overheats?

 

[Fun Times]

Welcome to iboats, are you able to get a video of the water spraying out and post it?

Where does the boat live during the winter?

If you're able to safely, try feeling the back side of the impeller pump housing by the hoses for excessive heat while the engine is running....Sometimes Bravo 3's need a water prime to get full water flowing vs a mixture of water and air.

 

[CurrentObsession]

Welcome to iboats, are you able to get a video of the water spraying out and post it?

Where does the boat live during the winter?

If you're able to safely, try feeling the back side of the impeller pump housing by the hoses for excessive heat while the engine is running....Sometimes Bravo 3's need a water prime to get full water flowing vs a mixture of water and air.

 

[CurrentObsession]

I have videos but apparently they are too large a file.

Winter on a trailer in Michigan.

I am very confident I winterized the block and manifolds adequately by pulling blue plugs and inserting wire up into it so all water would drain out before reinstalling the blue plugs.

 

[Scott Danforth]

running without cooling water, you burned all the rubber bits in the exhaust.. so the flappers and the rubber exhaust hoses are toast.

pull the exhaust elbows and inspect the rubber bits

look up your cooling flow diagram for your motor, or post your serial number and someone can post it.

water will always flow to the exhaust, however may not be flowing to the rest of the motor. have you pulled your t-stat and inspected that area?

 

[CurrentObsession]

running without cooling water, you burned all the rubber bits in the exhaust.. so the flappers and the rubber exhaust hoses are toast.

pull the exhaust elbows and inspect the rubber bits

look up your cooling flow diagram for your motor, or post your serial number and someone can post it.

water will always flow to the exhaust, however may not be flowing to the rest of the motor. have you pulled your t-stat and inspected that area?

Motor number ol605421

Will work on Tstat today

Thank you!

 

[Fun Times]

Motor number 0L605421

1998 Stern Drive 502 MAG [BRAVO MPI] [4752027M1] - Parts Lookup | Crowley Marine

View parts diagrams and shop online for 4752027M1 : 1998 Stern Drive 502 MAG [BRAVO MPI]. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.

www.crowleymarine.com

454 MAG. MPI BRAVO (GEN VI) GM 454 V-8 - 0L085400 THRU 0M024999

454 MAG. MPI BRAVO (GEN VI) GM 454 V-8 - 0L085400 THRU 0M024999

www.mercruiserparts.com

Thermostat Housing and Hoses

Thermostat Housing and Hoses

www.mercruiserparts.com

 

[nola mike]

. Water spraying out of the back SB side of the engine down low, I can't tell if it's a cracked manifold or where the head meets the block.

Umm, @Fun Times ,@Scott Danforth , did you guys miss this part?

 

[Fun Times]

Umm, @Fun Times ,@Scott Danforth , did you guys miss this part?

No sir, sure didn’t miss that part thus the reason I asked
Welcome to iboats, are you able to get a video of the water spraying out and post it?

Where does the boat live during the winter?

And he responded in post number 4.

Personally I think something unfortunate happened during winter but it will have to be up to CurrentObsession to physically get in there and determine the cause… Hopefully it’s a missed water drain plug or water hose but .

 

[CurrentObsession]

Short video and pic of T Stat

Is it a bad idea to run with TStat removed to see if it still overheats?

 

[Scott Danforth]

Is it a bad idea to run with TStat removed to see if it still overheats?

Yes

The thermostat in a marine motor is used as a mixing valve

 

[CurrentObsession]

Tstat opened up good at 175 and closed at 158.
I assume that means that's not the issue.

 

[Scott Danforth]

I would still replace it. It should be a 160F thermostat

 

[CurrentObsession]

Update:

Tried to disassemble the rubber boots on the SB side of SB motor today, didn't take too long to realize my logic of disassembling from the manifold risers back to the y boot wasn't going to work without pulling the motor as the bolts that hold the risers in place are much longer than the vertical clearance I have on that side. I spend enough time back there to realize that the boot going down from the SS vertical part of the silent choice exhaust was loose and had fallen down enough to have a slight gap between the boot and the cast iron Y pipe. I was able to manipulate it high enough and get some clamps on it to stop the leak, at least temporarily.

I went with a mechanics suggestion to check water flow at the T Stat housing by pulling the hose that comes up from the oil cooler line as seen on the attached video. Considerably less flow coming out of SB vs Port. Checked to see that there were no noticeable obstructions where the water enters the oil cooler as I was told that is the place most debris collects as it has the smallest perforated holes for water passages.

Attached is also some pics of how the temp is less on SB at idle but considerably higher when at 1200 RPM for a little bit.

Visually observing the exhaust with the loud mode on it is noticeable how much less water is discharged with the exhaust from SB vs Port motor especially on the SB side on the SB motor.

Any suggestions are welcome.

 

[Fun Times]

Yesterday I intended to mention that since the water appears to be spraying vs pouring out, it may indicate an exhaust type leak vs say a cracked open block or drain valve, etc. but never got back to you on it...Very glad it was way less severe than feared.

In the very front of engines with the water hoses attached that we can see, are those sea strainers? If so, you've opened them up and checked them to be clean? The seal is still tight?

How is the water intake set up on your boat? Through the stern drives or below the water line through hull marine type fittings?

Are you able to back flush the cooling system?

Does the boat sit in a marina/water or trailer and clean, etc.?

 

[CurrentObsession]

Yesterday I intended to mention that since the water appears to be spraying vs pouring out, it may indicate an exhaust type leak vs say a cracked open block or drain valve, etc. but never got back to you on it...Very glad it was way less severe than feared.

In the very front of engines with the water hoses attached that we can see, are those sea strainers? If so, you've opened them up and checked them to be clean? The seal is still tight?

How is the water intake set up on your boat? Through the stern drives or below the water line through hull marine type fittings?

Are you able to back flush the cooling system?

Does the boat sit in a marina/water or trailer and clean, etc.?

The boat is in a marina slip for the summer. I will pull the strainer out today and take a closer look. Water comes from the drives. I just had the drives serviced with new boots and new steering swivels so I assume the mechanic would have noticed Bravoitis. Boat was never in salt water according to the seller.

Not sure how to back flush.

Thanks

 

[CurrentObsession]

Update:

After much trial and error I have determined that there is a restriction between the high pressure side of the impeller pump and the inlet at the Tstat housing. I have been told that the only part of this pathway that collects debris is at the oil cooler which I confirmed prior is clean. What is the blue and yellow plastic thing inline between the power steering cooler and the cool fuel cooler? (Pic atttached)
Buddy at the Marina says it looks like a check valve but I have flushed and back flushed past it and if its providing any resistance its from its proper flow from impeller to tstat.
I'm thinking this is likely my problem.

 

[Fun Times]

Yes that is a check valve to help keep hot water from getting to the fuel cooler pump system… Merc part number 21-862271A1.

It could be an issue… but I just now saw where you mentioned you had bell housing type service work done… I would first thoroughly double check the intake waterline hose located on the outside of the boat between the bell housing and the transom assembly. I would suspect the hose has a twist or kink in it from working on it… it’s common to get that twisted up even if you’re trying to be careful.

Bravo 3 High Speed Overheat

Thank you in advance for your help and input. I have a Mercruiser 305 paired with a Bravo 3 drive on my 2006 Sea Ray 240SD. I do not have the serial number readily available. Last week I started having high speed overheat issues. Anytime I was over 3000 RPM the engine temp would rise and the...

forums.iboats.com

Here’s what the check value looks like in a package new,

https://www.riverdavesplace.com/forums/attachments/image-jpg.508946/

 

[CurrentObsession]

Update:

I fixed it by flushing and back flushing with water and air compressor until the check valve prevented backflow. I was surprised how much debris came out.

Thanks everyone for you help and insight.