Hot 150 - Possible fix?

[achris]

Re: Hot 150 - Possible fix?

S.C.<br /><br />Here's another idea that may help isolate something. Move the temp sensor to the other head. This will tell you if you have a problem with that head or the main cooling system.<br /><br />Chris...........

 

[garyj]

Re: Hot 150 - Possible fix?

achris60,<br /> The sensor that is connected to overheat alarm is located on the starboard head. I installed a sensor on the port head and connected a temp gauge to it. The temp gauge reads about 230 when the alarm sounds. I think the alarm is set to go at about 240 degrees. Seems both heads are running hot.<br /> I did try something yesterday while running the motor. I ran it up to about 210 degrees for about 3 to 4 minutes just before I reached the boat ramp. I shut down without idling. Put the boat on the trailer (didn't use the motor to drive on). The reason I did this is I'm thinking if I have a head gasket problem, it may only show up under high rpm's and not at idle. (If it idles for a bit, all the spark plugs would be wet with oil) This morning I removed the spark plugs for a check.<br /> THIS is what I found. Five of the plugs looked like the one on the left. The middle cylinder plug on the starboard side looked dry and clean (the one on the right). Thinking I may have a head gasket problem concerning the middle cylinder. I then removed the head covers and heads on both sides. I can't visually see a problem with either head gasket. Not sure if I should be able to detect a problem with the gasket if it only leaks under extreme pressure. I am having the heads surfaced (milled) to check for warpage. Anything else I should be looking for? Are these plugs telling me I have a problem, or is this just typical?<br /><br />Southern Catfisher

 

[achris]

Re: Hot 150 - Possible fix?

Gary,<br /><br />You may be on to something there. When you pulled the heads, did the piston crowns show the same as the plugs? I had a 200hp totally destroy itself couple of years back (I only work on boats as a hobby and to keep my hand in now-a-days). When I pulled the heads one side was dry (the right hand side). The other side was nice and oily, as I would have expected. I now had to find out why she went 'bang'. Further investigation showed that the fuel pump diaphrams had been replaced since new (1994) and (I think this is the one that really cooked it up) the throttle shafts were all quite worn. What this does is allow extra air into the manifold, making the mixture very lean. This increases cylinder temperatures and the pistons expand and try to be bigger than the hole, not good. So, where does this leave you? Go and check for throttle shaft wear. Grab the throttle shaft and try and move it up and down and side to side. If you get any movement you have worn shafts/carb bodies. GET IT FIXED! That cost my customer $3,000 for a block rebuild. He was happy with the end result though. <br /><br />Chris...........

 

[KCLOST]

Re: Hot 150 - Possible fix?

How do the cylinder walls look?

 

[garyj]

Re: Hot 150 - Possible fix?

achris60,<br /> The crowns of all the pistons looked about the same (slightly oily) with the exception of the middle piston on the starboard side (the one with the dry spark plug). It looked to be a little drier than the others but not discolored or damaged. <br /> I also checked the play for the throttle shafts for each carb. Seem to be in good shape, No loose motion.<br /><br />KCLOST,<br /> The cylinder walls all look GREAT!! with the exception of the top cylinder on the port side. At the very top of the cylinder, from down in the cylinder to about halfway out, is a couple of very fine scour lines. These are barely noticeable and are very smooth. Do you think this would cause me any future problems?? <br /><br />Also, got the head gaskets today and they have the smaller holes for the water transfer.(smaller than the originals) I've seen this issue addressed in another post. Is it still the general consensus that these are the correct gaskets?<br /><br />Southern Catfisher

 

[achris]

Re: Hot 150 - Possible fix?

Gary,<br /><br />That drier cylinder would be concerning me. Why is it drier? Possibly worth checking carb float levels or blocked jets. All the cylinders should look the same, slight oiliness to them.<br /><br />Chris........

 

[garyj]

Re: Hot 150 - Possible fix?

achris60,<br /> Is it possible that a leaking head gasket at this cylinder would cause it to appear drier??<br /><br />Will get the heads back Wednesday or Thursday. Hopefully have it back in the water this weekend for the fourth. (going camping up on the Alabama River -- need my boat!!!) If this doesn't correct the overheating problem, I will definitely take a look at the fuel system. It just may be running toooo lean. Who knows?????<br /><br />Southern Catfisher

 

[KCLOST]

Re: Hot 150 - Possible fix?

You have the correct head gasket... The smaller water passage holes were changed about the same time your engine was manufactured...

 

[garyj]

Re: Hot 150 - Possible fix?

Just an update and another question.<br />The guy at the machine shop where the heads were surfaced, said there was definite problems with the heads. Had to take off almost 20 thousandths to clear. He also brought up another issue. Apparently over the life of this motor, it has been in salt water and not properly flushed. There was scale and corrosion buildup in the heads. This is also true in the block area. <br />Is there any type of chemical flush recommended to remove this buildup? <br /><br />Southern Catfisher

 

[achris]

Re: Hot 150 - Possible fix?

Mr Southern Catfisher,<br /><br />I saw a product about 8 years ago that had a small bottle attached to the flushes. It draw the liquid in when the engine was run. Don't know how good it was though.<br /><br />Chris...........

 

[2springers26]

Re: Hot 150 - Possible fix?

Make sure the popet valve SEAl..( the one in the block) Is NOT loose or getting loose when hot.. have seen them work loose & hang the popet up.. & over heat..... merc now stakes the seal in place.....

 

[garyj]

Re: Hot 150 - Possible fix?

achris60, <br /> Thanks. I ran a search on the internet, and I came up with this Flush Kit. I believe it it manufactured down your way in Australia. I have requested some information from the manufacturer.<br /><br />2springers26,<br /> I inspected the poppet valve seal. Seems to be intact. Thanks for the tip.<br /><br />Reassembled the motor last night. Ran it on the muffs for about 20 minutes. Everything is cool so far. Will be up on the river for about four days. Will update with cooling results. Wish me luck!!!<br /><br />Southern Catfisher

 

[achris]

Re: Hot 150 - Possible fix?

Right on Gary. Soon as I saw it I knew that was the one I saw 8 years ago.<br /><br />By the way, good luck for the weekend..............<br /><br />Chris.........

 

[garyj]

Re: Hot 150 - Possible fix?

An update:<br /> Well, I have bad news and more bad news. First, the fish weren't biting... Second, I still have an overheating problem. <br />Thought I had licked it with the head gasket replacement. Not true. I am beginning to think now that is not water related but a lean condition. What makes me think this is I removed the exhaust divider plate to check for a possible leaking gasket. (no leaks) What I saw then has really peaked my interest. The middle cylinder on the starboard side had an extremely dry exhaust. Take a look at the PHOTO of the exhaust. Notice the dry cylinder (circled in red). This is the same cylinder with the dry spark plug. I removed the middle carb, and meticulously disassembled it looking for any blockage (high speed, low speed jet, vent jets, float levels, etc..). Did not see anything out of the ordinary. Question is, could I have a reed problem with this cylinder that could cause it to run lean?<br /><br />Thanks for any help...<br />Southern Catfisher

 

[achris]

Re: Hot 150 - Possible fix?

Hi SC,<br /><br />My first reaction to the photo was "Not good!" A reed could cause it, but you'd notice a drop in performance. A quick way to check reeds is to put your hand near the carb and see if you can feel any 'blowback'. Usually you'll find a lot of fuel on the air box too. You may have to start looking for those unusual faults we love so much, cracks in the carb body, leaking crankcase seal, ect. What about the bleed hoses? They have check valves in them. Or at least the nipple they connect to is a check valve. I've sent you a connection diagram. <br /><br />Chris..............

 

[garyj]

Re: Hot 150 - Possible fix?

Chris,<br /> Thanks for the diagram. Will check the bleed hoses. I'm thinking the same as you about the performance. It runs extremely well, which would probably indicate the reeds are good. There is no excess fuel/oil around the airbox either. I will need to reassemble everything to check for blow-back at this carb. I am really stumped here, but I do think this may be the root of the overheating problem..... <br /><br />EDIT: I checked the bleeder hoses. There is no bleeder hose or connection for the No.3 cylinder jug, and no connection for this hose at the E (No.6) reed block. What gives??? All other bleeder hoses are intact.<br /><br />Southern Catfisher

 

[achris]

Re: Hot 150 - Possible fix?

Gary,<br /><br />Read the diargam I sent you, bottom right. Looks like someone has replaced the block at some stage. Wonder if it was because #3 cylinder burnt up?<br /><br />Are you aware that the carb in front of each cylinder may not feed that cylinder? If it has horizontal reed blocks the carbs 'cross feed'. ie Port throats feed starboard cylinders.<br /><br />Chris............<br /><br />Edit : you have mail....

 

[jim dozier]

Re: Hot 150 - Possible fix?

This is just an aside to the overheating problem (Hope you get to the bottom of that). Removing 20 thousandths from the head will have significantly increased your compression ratio. Usually you don't want to remove more than 5 thousandths to clean up a head surface. I can't tell you how much the compression ratio went up without the engine measurements but I would guess at least half a point(i.e from 8.5/1 up to 9.0/1). You probably should go up a least one grade in gas octane to prevent pre-ignition and detonation. Generally, if a head needs that much milling I would look for another used head that wasn't as warped and mill it 5 thousandths.

 

[garyj]

Re: Hot 150 - Possible fix?

Just an update:<br />After finding the dry cylinder, I broke down and took it to the dealership. After much debate, the diagnosis was that ALL cylinders should be dry. There is no bleed hose connected to the #3 cylinder, therefore excess fuel is not redirected to this cylinder. A mercury master tech says that now, they block all the bleed hoses (using a bb) so that no excess fuel is routed to any cylinder. This is what they have done. Now all cylinders are dry. Also, to check the overheating problem, they have went through the carbs looking for a lean condition, checked the timing and all switch boxes, etc.. Did not find anything. Checked the water pump and installed restrictors in place of the thermostats. It's still running hot at high rpms. They were supposed to install a water pressure gauge. Didn't happen..back order. (It tough to live in a small town). The gauge should have been in this week. This would let me know where to look next. The tech says that not enough pressure would indicate air intrusion into the cooling system, or pump or gasket problems. A higher than normal pressure would indicate an obstruction in a water passage. Well, the gauge did not come in, so this morning I made the 180 mile round trip for the gauge. Got it installed and took it for a test run. I had about 5 lbs psi at idle. I wanted to see what pressure I would have at wot. I knew that I would need to get it to wot as quickly as possible and take a reading as it will run hot if I hold it too long. Got it up to about 5500 rpms, 60+ mph, had about 20 lbs of pressure, running about 215 degrees. All of a sudden, it started missing on one cylinder, and before I could throttle back, the engine seized!!!!. That was a wild ride.... After sitting about five minutes, I finally got it to start. Would only idle. If I gave it any throttle it would die. When I put it in gear, it makes a bad knocking sound it the top of the engine. Did manage to limp back to the dock.<br />This is where I am. This motor has made its last trip with me to the river. I have spent about 400 dollars trying to locate the overheating problem. I am not throwing away more money on this engine. Tomorrow I will begin the hunt for a Johnson or Evinrude to replace this engine. This was my first and last mercury!!!!!<br /><br />Thanks for letting me vent...<br /><br />Southern Catfisher

 

[achris]

Re: Hot 150 - Possible fix?

Hi Gary,<br /><br />Sorry to hear about the dead engine, and sorry to see a good man going to the 'dark side'. <br /><br />Chris................