How to properly diagnose head gasket failure 5.7 Mercruiser RWC.

[dwolsk2]

Hello My name is Dan and obviously I'm new to the community.
I've been reading up on old posts similar to my problem but haven't actually seen a response to testing for head gasket failure on a RWC engine, everyone seems to have a heat exchanger.

I purchased my 3rd boat sight unseen on Ebay. I am very well aware that was a terrible mistake.
1998 Maxum 2700SCR. from Maryland, Chesapeake bay boat
Well the boat sat at a marina, I'm assuming for 8 years (last registration decal expired 2007)
The engine is a 2-barrel carbureted 5.7 Mercruiser coupled to a Bravo 2 outdrive. I'm not sure of the serial numbers but i did find a tag with a unique Jasper engine number. I called Jasper engines with the info and they stated the engine was rebuilt in 2006. ... that seemed promising.

So I've been trying to single out the problem with my overheating at higher rpms. At idle and up to roughly 3000 rpms the temperature holds at 175 (160 thermostat)
Anything beyond that the temps climb and the warning system kicks in.
Here's the list of items i had replaced along with tests i've performed.

1.Bellows, water pickup, gimbal bearing, new raw water pump, engine circulating pump.
2. intake manifold gasket, ( was whistling through the pcv port. internal vacuum leak, this was probably the first mechanical repair i had done to this boat)
3. rebuilt carb... that was a mistake. The rebuilt carb was dumping fuel into the intake, causing very hard starts. I installed the old original carb and it runs perfect.
4. electric fuel pump. The fuel delivery problem was not the pump.... the purple wire off of the alternator was grounding at the motor mount.
5. new risers, manifolds, and elbows. I chose the HGE aluminum ones from Michigan Motorz
back flushed the cooling system.
6. siphoned 90 gallons of 8 year old fuel out of the tank.
7. basic tune up, new plugs NGK BPR6EFS, distributor cap, rotor, plug wires. ( here's a bit of advice on my end be careful purchasing complete tune up kits on ebay, i was sent a rotor for a 6 cylinder Merc.... it took me a while to catch the reason i had 2 dead cylinders.
8. installed clear hose at the sea water intake ( even a 4" section is collapsing under the suction the pump is creating ) Installed clear hose at thermo housing on the outlet side of the pump. ... bubbles are present coming in before the pump at idle, I'm assuming those are the exhaust gases? and then showing up again at the thermostat housing. i did install a clear hose to the bottom of the port manifold. Bubbles were present but i need splice a short section since the clear hose had too many kinks and it caused improper cooling to that manifold.
9. completed the flow test of the seawater pump. Roughly half of the 5 gallon bucket fills in 15 seconds.
10. Compression test resulted in each cylinder at 180 psi or above.

In addition i also have a small oil leak that i'm assuming is drive oil. (it's visible in the water near the outdrive) Unfortunately i haven't been able to notice any loss in oil levels ( engine, drive, power steering). I only mention this because i feel that maybe when i had torqued the drive back on to the gimbal one of the o-ring seals possibly failed to mate correctly, causing the oil leak and allowing exhaust gasses near the water pickup tube? I haven't been able to test this theory since the boat is in the water.
The motor idles perfectly at 600 rpm, no bogging on acceleration and no steam visible in the exhaust at lower rpms. Around 3000 rpm (not underload) a little bit of steam seems to appear.
Oh and probably most importantly the overheating in the higher rpm range occurs only under load, not if i just throttle it up in the slip.

I'm not sure if this is relevant but my oil pressure is high at idle. Cold almost 80psi, Once it warms up it's closer to 60 psi. I've actually seen it down to 40 at one point. I went with Amsoil's marine 10W-40 hoping it would lower the oil pressure readings. I checked with a mechanical gauge and there was only a 5 psi variance (60=55 on the mechanical gauge)

If anyone has any other suggestions, tests, i am open to try them.... otherwise i feel it's a head gasket or cracked head.

Thanks

Dan W

 

[NHGuy]

Your cooling water has air in it. Before you condemn the engine make sure you are getting the designed amount of cooling water and no air. Chase your way back toward the water intake til you find the air source. Also you said the clear hose collapsed from suction. I realize it's not the spec hose but if there's tons of suction perhaps there's a blockage in your water intake, Back blow it out &; disassemble whatever you can. You'll probably need to pull the boat out of the water for that though.
If you find no issue you can still test for head gaskets, etc like any engine.

 

[Bt Doctur]

There is a water passage O ring between the upper and lower unit that could be damaged , the Bravo`s do have a corrosion problem closing off the water hose at the gimbal, and at the transom housing.

 

[dwolsk2]

Thanks guys for the quick responses.

I am more than willing to continue to look for a water restriction then start with the head tear-down.

-NHGuy I'm assuming by your response there should be zero bubbles coming in on the inlet hose from the transom? Where could air come in from if the outdrive is submerged? I may have over exaggerated the collapsed clear tube on the inlet side. It does collapse but water still flows through it, and of course random bubbles.... I'm planning on taking a few videos later on today to post.
I had checked the threaded insert yesterday on the inside of the transom, i was curious if it had collapsed... seen it on other posts. Though i had done the bellows and the water hose myself last year and those inserts/hose are basically brand new.
I had looked throughout numerous posts on what the rate of flow should be coming from the transom into 1 1/4" inlet hose ... without the sea water pump running. Right now it seems low, but then again that is a 5/8" water hose. I'll try to video tape that flow as well.



-Bt Doctur I have never separated the lower unit of the out-drive from the upper unit on this boat. Is this difficult? Could this possibly cause my slow oil leak?
Obviously that's an out of water activity to check. Just trying to isolate all the problems while I'm in the water before i make the commitment to pull it out.

thanks again

Dan W

 

[NHGuy]

I am completely out of my element on your drive. But it is my understanding that you should have no air bubbles if the concept on smaller drives is the same.
Air can get in through a leak in the suction side of the water supply.
BT doctor is a super resource. I'd follow his lead.

 

[dwolsk2]

Ok as promised i took some videos with clear tubing installed. I apologize if the quality is bad but i was alone and i tried to show the various conditions at different rpms.
This first video has a short section of clear tubing installed on the inlet side of the water pump, you can see the flow towards the end of the video. It somewhat caused the hose to collapse and i'm assuming because of the poor flow it seems the air showing up at the thermostat is quite abundant.

 

[dwolsk2]

In this video I removed the clear hose section from the inlet side. Therefore, there should be no hose collapsing causing water flow issues from the transom.
If you look closely bubbles are still visible.

 

[dwolsk2]

In this last video. I ran the engine up to 3000 rpm. I could be wrong but the water flow appears to stop.
I had a video showing flow through the 1 1/4" inlet hose from the transom but for some reason that video became corrupted.
I'll try to get that done again later this week.

Any ideas?

-NHGuy thanks for the responses. You obviously know a lot more when it comes to boats then i do. Any advice is always appreciated.

BTW this time the temps creeped up over 175 when i ran the engine at high rpms in the harbor... didn't get high enough for the alarms to kick in though.

thanks for all your input thus far

Dan W