Belt came off, engine overheated, water in 3 cylinders

[dpickett]

Looking for some advice on what do with my (hopefully not blown) engine.The boat is a 2000 21V, 730 hours, Mercruiser 5.7 Mag MPI engine. Just bought it this spring. I finally got the wave dialed in, only to possibly kill the engine.

I went surfing today, and then cruising around after emptying the fat sacks. I started hearing a loud beeping noise and finally realized the engine temp was around 200-220. I looked at the engine and realized the belt had come off, so I shut it off. It probably ran for a minute or two while overheating. First time boat owner, so I didn't realize what the beeping was.

After calling a friend, waiting about 10-15 minutes, and getting towed back home, I got the boat on my lift. I put the belt back on, hooked it up to my hose that I use to flush the engine (I'm running the boat in brackish water), checked the temp (was back down), and tried to start it. It didn't crank at all. On the advice of a friend, I pulled the plugs and had water in 3 of them. I sprayed some WD40 in them all, and cranked for a few seconds about 5-6 times until it seemed like all the water was out. Then, I sprayed more WD40 in all of them.

Any advice on next steps? I'm hoping I don't need a whole new engine. How do I figure out how much I broke?

[boatwakes]

Get it running ASAP!!! Check the oil for milkshake color but plan on changing it anyway. THEN FIGURE OUT WHY THE BELT WAS THROWN. Usually pulley alignment from the upper adjustment pulley bearing failing but other pulleys have been culprits as well. Report back when you can and we'll go from there.

[dpickett]

Thanks for the advice. From what I've read online, it sounds like I may have just sucked up water through the exhaust when I shut it down. I've read two possible reasons: slowing down too quickly swamps the back and the overheated engine creates a vacuum. I'm not sure which is correct, but hoping I didn't crack the block or heads or ruin the head gaskets. I do have a Fresh Air Exhaust, not sure if that helps in figuring out what caused the problem.

I'm assuming you are saying to get it running ASAP because there is salt water in the engine now? One of my spark plugs broke when I loosened it, and the other seven didn't look to be in good shape. I think I'll go buy these from West Marine rather than wait two days for Amazom to ship me the Quicksilver ones.

I forgot to mention in my earlier post that when I pulled the dipstick, the oil looked fine. But, I'll change it anyways. So, change the oil and plugs and then fire it up?

[chpthril]

With the plugs out, run a compression test. Any low cylinders, then do a leak down test to see where the air is going.

[dpickett]

I changed the oil and oil filter and then tried to do a compression test. I'm confused by the results and not sure if I did something wrong. Here's what I did:
- took out all the spark plugs
- connected a remote start to the starter slave selenoid
- left the key off
- the first time, I forgot to open the throttle

When I did the test, the compression went up to 210 and was still rising, so I stopped. I tried another cylinder and had the same result. While testing the 2nd cylinder, I noticed that the belt came off. I put it back on and tried again, same result.

Then, I realized I didn't open the throttle (I'm interpretting those directions as pushing the throttle forward). So, I put the belt back on, pushed the throttle forward, and tried the compression test. The belt stayed on, but the compression went up to 210 again. I stopped there.

Any ideas what is going on? Is the belt coming off causing the compression to go so high? How can I diagnose what is causing the belt to come off?

[chpthril]

If the engine IS indeed toast, the belt coming NOW is moot. However, for a compression test, I dont see the belt being on or off, a factor. Leave it off and check compression on all 8 cylinders under the same conditions. Usually, 3-5 engine rotations and you get the cylinder's peak compression #. Move to the next cylinder.

Just make sure you note the compression for the proper cylinder. This way you can compare it to the 3 that had water.

[freeheel4life]

Take a look at the raw water pump, bottom pulley port side. Bearings fail and shaft wobbles/moves in and out.

[dpickett]

I did the compression test on all the cylinders this morning. I used a remote start, had the throttle forward, key off. Here's the results (sorry, I don't know the correct numbering for the cylinders):

Starboard side (bow to stern)
1) 210
2) 205
3) 220
4) 215 (had water when I pulled plugs on Sat.)

Port side (bow to stern)
1) 205 (had water when I pulled plugs on Sat.)
2) 240
3) 220
4) 230 (had water when I pulled plugs on Sat.)

When a mechanic inspected the boat before I bought it in May, all the cylinders were between 155 and 170.

I'm not seeing a pattern between the cylinders that had water in them and the ones that didn't. It just looks like they are really high. Any guesses on what would cause the high compression or what to do about it? I'm sure the water in the engine could cause that, but it seemed like all the water has been blown out of the cylinders.

I checked the pulley on the raw water pump. It didn't seem to wobble or move in and out. However, it was difficult to turn. I'm not sure how hard it should be to spin, but it definitely didn't spin freely like the pulley for the alternator. Is that normal?

[chpthril]

Any guesses on what would cause the high compression

High compression is good compression.

The previous test may have been throttle closed. Could have been with only the plug of the cylinder being tested, removed. All other 7 plugs still in. Could be a difference in the 2 gauges used. I would not worry about the previous test. The lowest is a little out of the 10% rule of the highest, but one of the 2 lowest did not have water and they are on different sides of the block.

Starboard side (bow to stern)
7) 210
5) 205
3) 220
1) 215 (had water when I pulled plugs on Sat.)

Port side (bow to stern)
8) 205 (had water when I pulled plugs on Sat.)
6) 240
4) 220
2) 230 (had water when I pulled plugs on Sat.)

I think this is the cylinder order.

[dpickett]

Think I should put the new plugs in and start it up?

[chpthril]

As boatwakes suggested, get it running ASAP. The water, especially salt/brackish, is bad for the internals of an engine. If its toast, running it really wont make a difference. If tis not blown, you are good to go, but letting it sit is bad.

No on the new plugs right now, just get it running.

[dpickett]

Okay, thanks. I put the old plugs back in (except one that broke when I took them out Sat, I replaced that with a new one). It took a couple of times cranking and it fired up rough, but then ran at idle okay. Oil pressure and temp were fine. I only ran it for about 3 minutes because the belt came off again and I wasn't sure if that would cause a problem. Is that an issue to have it running on my lift hooked up to the hose with the belt not on? I'd like to run it longer to get enough Salt Away through the engine to clean it out.

I guess my next step is to determine why the belt is coming off. Is the raw water pulley supposed to spin free and easy? Mine definitely does not. Any other ideas on how to diagnose why the belt is coming off?

[chpthril]

On the water or on the hose, no belt = over heating. At this point, id say you are good to move forward with resolving the belt issue.

Start by eyeballing the pulley alignment. Sometimes its easily seen when looking.

[freeheel4life]

Raw water pump is hard to turn because the impeller contacts the housing inside. Its especially hard to turn the opposite direction of normal rotation until all the vanes flip over. So yes, it shouldn't turn freely like Idler, tensioner, or circulation pump pulleys

[dpickett]

All the pulleys seemed to be in line with each other.

I decided to check the impeller because I didn't know that it's normal for it to not spin easily (thank you for answering that question freeheel). Figured it wouldn't hurt to change it out anyways. Man, that was a pain to get off. Really hard to get to the bolt heads. I ended up having to take off the two hoses because one of the bolts was stuck. I got the whole assembly out and sprayed some penetrant on the bolt and plan to leave it overnight. The impeller appears to be in okay shape from what I can see.

I attached some pictures of the belt. Does it look like it needs to be replaced? I suspect it does, but it doesn't seem bad enough that it would cause it to come off every time I run the engine.