Reply
 
Thread Tools Search this Thread Display Modes
 
Old 09-11-2014, 11:20 AM   #1
Lt. JG
 
Join Date: Jul 2013
Location: Warrenton, VA
Posts: 16
Default Possible Blown Head Gasket - Options

Regret the long thread, but decided to provide full details for best responses/recommendations.

The engine is a carbureted (Weber 4 bbl) 1997 Model Mercruiser 7.4L Bravo in a 1998 Maxum 2300SC. It is the original engine.

About 3 Weeks ago, started experiencing engine stall after running at WOT for a couple minutes or so. Also, if at WOT for a shorter period, engine would stall when backing off rapidly from WOT.

Engine would eventually restart, if treated like a Flooded Engine restart. Would run rough for a few seconds then smooth out. I could motor all day long at under 3000 RPMs with no problem. I could even go full throttle to get up on a plane, but as long as I backed off the throttle as plane was reached, she ran fine. No evidence of fuel obstruction or fuel starvation or oil contamination at all. No evidence of overheating – engine temps remained in the 150-160 degree range when warmed up. Oil pressure was fine. No leaks of any type found around engine.

Brought it home, did some research and decided it was time for some TLC and maintenance since pretty much everything except for plugs on that engine is Original on it since boat was new. Boat has about 450 hours total time, but is 17 years old, and was used in salt and brackish water the first couple years, before being used exclusively in fresh water lake. I replace the seawater pick up pump impeller annually, as well the Oil Filter, Fuel/Water Filter, the additional “in-line” glass fuel filter element and stern drive oil, all during the winterization process each year.

Here is what was done in the last week.

1) Removed and Checked Anti-Syphon Value. No obstructions. Functions normally.
2) Removed and replaced Full Fill Hose, Full Feed Hose, and Fuel Vent Hose. (Preventative – no problems or obstructions found, just figured it couldn’t hurt to put new hoses on considering the originals were 17 years old).
3) Replaced Plugs, Ignition Wires, Rotor, Distributor Pickup Module, Distributor Cap, and Ignition Coil. Old coil was found to have some very slight “slush” when shaken, indicating possible loss of oil from inside.
(I noted that the #6 Plug when removed was not at the appropriate “gap” of .35. It was slightly closed at .30, and showed evidence of possible weak ignition (electrode insulator was white, not slightly light brown like the others).

While I was at it and considering the boat was 17 years old and still had the original exhaust system on it and that the first couple years when new, it was used in salt and brackish water and then used exclusively in lake/fresh water. I did the following.

4) Replaced Exhaust Manifolds, Risers, and Exhaust Elbows. (They didn’t look bad considering their age, but some build up was noticed in the riser water ports, making me feel better that I decided to just replace everything now). Of course, the installation included new exhaust manifold gasket, and new gaskets on the risers and elbows. The gasket between the 3” Riser and Elbows are “restrictor” gaskets. My original exhaust elbows had “drain” elbows on the bottom of them. The new elbows only came with the 90 degree elbow with no drain plug capability.

5) Replaced Thermostat, Sleeve, and gaskets. (Figured why not, those were original too).

While the spark plugs and the exhaust manifolds were removed, I ran a bore scope into the cavities for a visual inspection. Cylinder walls looked really good with no evidence of rust or pitting. Piston Heads look normal as well. Same positive visual inspection results from exhaust ports. Exhaust Valve stems and seat (from what I could see around the tops of the value seats) all looked good and did not see any evidence of oil seepage down the value stems.

Everything fired right up and tested fine in the driveway with muffs on. Oil was clean. She ran really smooth at idle. Took her down to the lake for an in-water test yesterday. She started right up again, motored out of the marine area at idle speed and continue to listen and visually inspect for any leaks around engine. All looked really good, so closed the engine compartment and ran her up to WOT. I did notice the RPM’s jumping around just a little, but it settled down. Oil pressure and Engine Temps were in perfect range. We did smell “something” a little funny, but it may have been paint on the new exhaust parts just heating up for the first time. No smoke or anything.

After about 3 Minutes or so, disaster struck! She stalled again, but this time, with more cough and sputtering. I did my usual inspection of the engine compartment. No leaks or anything else out of the order, but when I checked the oil dip stick, WATER had mixed in the oil for the first time. The engine would crank, (only tried for a couple seconds) so it wasn’t water locked, but at that point, I called for a tow back to the Marina and contacted the Marina shop for service. They haven't got to it yet, but I'm pretty sure they are going to tell me I have a blown head gasket.

Now, the question. A new long block 7.4L is about $5K. While the head gaskets can certainly be replaced on the original engine (assuming no other damage/issues or a cracked block), not withstanding and low hours on the engine, it's 17 years old, I'm thinking other gaskets or parts may be getting at the top end of service life. Am I better off just having them drop a new long block in and bolt up all my other parts to it including the new ignition and exhaust system, or because of the low hours on the existing engine, are just new head gaskets the way to go? I am concerned that the lower end has now been sitting in contaminated oil for almost a week now. I've heard of crank bearings rusting after being in contaminated oil.

Any advise and recommendations are much appreciated!

R/ Steve
__________________

cwolaw is offline   Reply With Quote
Old 09-11-2014, 12:57 PM   #2
Moderator

 
Join Date: Apr 2008
Posts: 3,553
Default

Did the engine die while you were up on plane? If so the following wake can catch up to the boat and cause enough pressure to go in the exhaust port, and back through the elbows and risers and flood the engine. This happened to me about 5 years ago. When the engine is running the exhaust typically creates sufficient back pressure to prevent this. The Y should also have shutters in them, but they are rarely 100% effective. A failed manifold or riser gasket can also cause the same water intrusion as well.

I'd try to nail down the ingress before deciding to repower.
__________________

__________________
Leave me alone, it's Boating Season!!!
shrew is offline   Reply With Quote
Old 09-11-2014, 01:04 PM   #3
Lt. JG
 
Join Date: Jul 2013
Location: Warrenton, VA
Posts: 16
Default

Thanks Shrew! Engine did die while up on plane, so not likely that a deceleration following wake caused it. As I research this further, since I did replace the manifolds, risers, and elbows, (and I must admit, working in tight quarters replacing the manifolds was a challenge), maybe I screwed the pooch with the manifold gasket and didn't get it right. I'd be pleased if it's only the manifold gaskets!
cwolaw is offline   Reply With Quote
Old 09-14-2014, 05:51 PM   #4
Admiral
 
mmwjr's Avatar
 
Join Date: Feb 2012
Location: Perry Hall, Maryland
Posts: 5,397
Default

Hi Steve make any headway on resolving your issue? Since you replace all of th exhaust with new parts I will be surprised if you have a poor gasket seal here.
__________________
Mike
mmwjr is offline   Reply With Quote
Old 09-15-2014, 11:08 AM   #5
Lt. JG
 
Join Date: Jul 2013
Location: Warrenton, VA
Posts: 16
Default

Quote:
Originally Posted by mmwjr View Post
Hi Steve make any headway on resolving your issue? Since you replace all of th exhaust with new parts I will be surprised if you have a poor gasket seal here.
UPDATE: Well, got the shop to get it in on Friday Morning. They confirmed water infiltration - really didn't take an expert to confirm that. Boat Started right up for them (brief test)! They were impressed. And she ran smooth. They were impressed again and three mechanics looked at each other and said, "he doesn't have a blown head gasket", but they pulled the plugs and did a compression test on all cylinders and confirmed, NOT A BLOWN HEAD GASKET. Further investigation, they pulled the oil cooler, and found a lot of debris from prior impellers that have disintegrated (note in my earlier post, I change the impeller at the beginning of EVERY season now - because I have in past had to performed two "in-water" impeller replacements - not fun on a hot engine). They cleaned it out, pressure tested the oil cooler - it's fine. Not the source. So, today, they are pulling the intake manifold to see if they can find anything telling under there. They still keep asking if there is any chance that it may have froze, since last winter was the coldest we've had with multiple days below freezing. She's been winterized the same manner for the last 15 years, and even after running the anti-freeze through the system and fogging it out, I drain the elbows and block, so any remaining puddles of water that may remain in the block "should" be treated anti-freeze. However, with all the impeller debris in the engine, it's possible that the rubber impeller material has clogged someplace, and that the anti-freeze didn't get to it, and that may have froze and cracked the block internally in some location. Also, when they pulled the block drains, they noticed contaminated oil, so the water infiltration is "both ways", not only is water getting into the engine, the contaminated oil has leaked back into the water jackets. Not Good. I doubt they are going to find anything telling when pulling the intake, so I'm holding on to my chair for the call today, that the engine probably needs to be replaced. I'll drop a new long block in instead of having the existing engine repaired (if it's repairable at all anyway). Cheaper in the long run to go this route. Since my ignition system and exhaust system is brand new, these can be used on the new block. Stay tuned! Updates to follow!
cwolaw is offline   Reply With Quote
Old 09-15-2014, 11:31 AM   #6
Lieutenant
 
Join Date: Nov 2006
Location: Richmond, KY
Posts: 50
Default

I recently discovered a cracked block in my boat and I've been racking my head trying to figure out how it could've happened. Parts of a disintegrated impeller lodged somewhere in the block, stopping flow of antifreeze, never thought of it. Maybe, just maybe that was my problem. The boat was 6 years old when I got it so there's no telling. Sorry for your luck but thanks for the detailed explanation of the situation.
scoutonwater is offline   Reply With Quote
Old 09-15-2014, 11:45 AM   #7
Admiral
 
mmwjr's Avatar
 
Join Date: Feb 2012
Location: Perry Hall, Maryland
Posts: 5,397
Default

The impeller pieces may also have blocked coolent flow causing a hot spot that resulted in a crack. I have heard of a few leaking intake gaskets lately so hopefully it is just that.
__________________
Mike
mmwjr is offline   Reply With Quote
Old 09-15-2014, 04:06 PM   #8
Lt. JG
 
Join Date: Jul 2013
Location: Warrenton, VA
Posts: 16
Default

Quote:
Originally Posted by mmwjr View Post
The impeller pieces may also have blocked coolent flow causing a hot spot that resulted in a crack. I have heard of a few leaking intake gaskets lately so hopefully it is just that.
Well, the Verdict is in! And not really a surprise. Intake Manifold is fine and no evidence of water infiltration from there, so the water got into the engine somewhere lower in the block. It could have been a port blocked and freeze related or even a blockage causing a hot spot as suggested. Doesn't really matter, as the end result was the same. But you can bet I'll be replacing the impeller annually from now on! A new impeller is far cheap than a new engine! Since I'm not going to get a core charge reimbursement with a cracked block, I'd love to be able to tear down the engine and look for that water source crack, just to satisfy my curiosity! We'll see if that's an option. So, looks like a Long Block is getting dropped in! Keeping with Mercruiser OEM 7.4L Pro-Series long block since it has a 3 yr parts & labor warranty. This really sucks, but, I can't complain. It's been a GREAT engine for 17 years! Total price is $9,700.00. Includes parts and all labor, including carb rebuild and new engine mounts (original mounts are rusted pretty bad).
cwolaw is offline   Reply With Quote
Old 09-15-2014, 04:11 PM   #9
Lt. JG
 
Join Date: Jul 2013
Location: Warrenton, VA
Posts: 16
Default

Actually thought, just for a few seconds, of going with the 502 instead of the 7.4L. But the intake manifold would need to be changed out and the 7.4L is probably far more fuel efficient than the 502. Not sure I really need the boat (loaded) to go over 55mph (as it does with the 7.4L). Wife says 55 is PLENTY. We spend most of our cruising between 30-35 MPH anyway. Smoother and quieter ride and best fuel economy at those speeds.
cwolaw is offline   Reply With Quote
Old 09-15-2014, 04:17 PM   #10
Admiral
 
mmwjr's Avatar
 
Join Date: Feb 2012
Location: Perry Hall, Maryland
Posts: 5,397
Default

I am assuming this is a rebuilt long block as this engine has not been made for some time.

You can block off the t-stat and try pressurizing the block to find the crack. About 15 psi should do.

Keep the wife happy and stay with the 7.4, she won't complain about the $'s as much.
__________________

__________________
Mike
mmwjr is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Powered by vBadvanced CMPS v3.2.3

All times are GMT. The time now is 11:19 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.