engine overheated

[dallas T]

A friend just purchased an '88 boat. Took it for a 2 hour test drive with no problems. The next day he took it out for a ride and it began to overheat. When he shut it down, there was a little smoke/smell from the engine compartment and the temp. gage read 190 degrees. <br /><br />He asked me to take a look after it had cooled down and mentioned that he may have run through some weeds and mud in a shallow end of the lake.<br /><br />The motor is a 3.0 liter (I think 130HP) OMC I/O. I asked him to forward the serial number since I fogot to get it.<br /><br />Here is what I did to help diagnose the problem.<br />1) got in the water and verified the outdrive water raw water input was not full of weeds and mud.<br />2) pulled the small (looks like 3/4") hose that goas from tansom to circulator pump (the pump bolted to the from of the motor) and turned over the engine. no water was pumping. <br />3)Pulled off the circulator pump and it looks fine (probably did not need to do this but did it anyway)<br /><br />So here are my questions:<br />A)I assume there is another pump or impeller in the outdrive, is this correct?<br />B)If so, is it located in the top end or the bottom end of the outdrive?<br />C)If there is an impeller in the outdrive, can it be changed / repaired with the boat in the water and is it an easy job for a backyard car mechanic?<br />D)Anything else I should look at?<br /><br />Thanks in advance<br />D)

 

[rbezdon]

Re: engine overheated

You need to post the Make and Model of the drive as well as the year. Must be an OMC Cobra, Merc Appha or Volvo but without that info it is hard to tell you where the impeller is and how tough to change. In most cases it is not extremely difficult to chang but different drives may require pulling off the outdrive. I do not believe in any if the cases that it is possible to do with the boat in the water.

 

[rodbolt]

Re: engine overheated

omc cobra can, stringer units cannot. the cobra unit has external hydrualic trim rams the stringer has a half moon shaped gear rack on the port side of the drive. purchase a service manual with your pump kit.

 

[rbezdon]

Re: engine overheated

Rod, I have a Cobra and change the impeller easily without pulling the drive (one of the things OMC did right) but I would hate to even try to change it in the water, it is just below water level and anything dropped is gone forever!!

 

[dallas T]

Re: engine overheated

I guess I just assumed it would be an OMC cobra because the engine is a OMC 3.0L. I will need to go see the outdrive and identify it as an cobra, stringer or whatever.<br /><br />My friend just called me with some model and serial numbers found on the motor valve cover. Not sure if this helps:<br /><br />model: 302AMRGDP<br />Serial: T1029715<br /><br />model: 985268<br />serial: T0544998<br /><br />I also called the local marine parts store and they had only one water pump rebuild kit listed for this year and motor. That number coresponded to the OMC cobra outdrive so maybe I am in luck with the easier installation.

 

[dpbj6]

Re: engine overheated

Go to this url. It is real easy to replace the impeller.. You first time, it will take you about 15 min. Just make sure the blades are faned the same way as the old one. and that then old one still has all it pieces. If not you need to backflush the system.<br /><br /> web page

 

[dallas T]

Re: engine overheated

thanks for the schematic! So just take it apart and put it back in the reverse, no special instructions... cool

 

[rbezdon]

Re: engine overheated

It is a really easy job but if you try it while the boat is in the water be careful, dropping the cover, impeller or what ever and usually its gone forever. This is really a piece of cake if your on the trailer, even the first time. Cobra is about the easiest drive to change the impeller.

 

[dallas T]

Re: engine overheated

Thanks for all the valuable information. Last night I carefully disassembled the old impeller (with the boat in the water). Inspection of the old impeller showed no obvious signs of damage. I went ahead and installed the rebuild kit and fired up the motor. After running for about 1 minute, I pulled the hose off to see if we had any flow. Still no flow.<br /><br />I dissasembled the impeller housing again and comfirmed that the impeller drive shaft rotates. I also dropped 1 bolt in the water (I know everbody warned me).<br /><br />With a garden hose, I checked for obstructions between the impeller and the motor circulator pump. No obstructions which eliminates a kinked line near the transom.<br /><br />I tried to push water through the impeller out to the bottom end of the outdrive and bingo, no flow.<br /><br />After running the garden hose for a while, I was able to free up some sand and sediment.<br /><br />Next I reassembled the impeller (with new bolt as the old one that fell in the water is gone forever). Fired up the boat and water flowed for about a minute and then stopped.<br /><br />So, I think I have a stuborn clog from the lower end inlet to the impeller pump. What is the best way to clean this out? I could try more water pressure to flush it out but wanted to check here first.<br /><br />Thanks again for all of your help.

 

[rbezdon]

Re: engine overheated

Sorry, I am not familiar enough with the actual structure in the lower to know of more pressure is going to hurt anything but you did make my day this morning and I got a good laugh about the bolt. I did the change and it is just easy enough that I knew it could attempted in the water and just clumsy enough that dropping something was a real possiblity. Glad it was just a common bolt and not something harder to find and more expensive.

 

[dallas T]

Re: engine overheated

I figured someone would get a laugh about the bolt. I was sooo carefull the first time I install but then got careless... <br /><br />Has anyone pulled the lower unit to clean the filter screen? Is this a simple job or does it involve tricks, experience and special tools to re-install?<br /><br />Thanks

 

[rbezdon]

Re: engine overheated

No way to pull the lower unit with the boat in the water. I would say pull the boat out, drop the L/U off and flush it throughtly with hose and as mush pressure as it gives. I think you are going to have a tough time to get a good flush with the L/U below water level. The lake water will "flod" the water intake as it is below water level and slow down the water flow from the flush.

 

[dallas T]

Re: engine overheated

I was going to wait 1 day and post a message that said "I tryed to remove the lower unit with the boat in the water and it slipped out of my hands and is lost forever".<br /><br />I will pull the boat out tonight. Does the lower unit simply un-bolt and drop down? No odd springs and loose parts to fall out etc?<br /><br />As for installation, just hold it up and bolt it in???<br /><br />Sorry for all the questions, just want to make sure I am not getting in over my head...

 

[rbezdon]

Re: engine overheated

There are a few odds and ends to take case of. You have to pull off the trim rams and there is some hardware there. The hinge pin goes through both rams and the drive with washers sandwaiched between but no big deal. Once you get the rams off at the drive end remove the 6 bolts. I had some trouble getting the drive to slide back but just pull and tug, it comes off. The drive shaft will kind of fall out once you get the drive most of the way off but obviously it is attached to the danger is in banging something, not loosing it. Make sure the shift is in neatral. The only loose thing is the outdrive gasket but since you are going to replace it if it tears etc no big thing. Make sure you replace the o rings on the drive shaft which lock it into the gimball bearing. When off you can see into the water tube where it mates to the transom assembly. This is above the impeller. You should be able to push water in there. Maybe even remove the impeller again and flush back from there. Putting on the drive there is a odd shape o ring for the water seal to replace. If you buy the gasket kit it comes with the two O rings, water seal and gasket for about $4. You might consider replacing the exhaust and drive bellows while your in there. Mine took another 1/2 hour or so and about $30 each. When going back on make sure to lube the splines with a spline grease, shoot the ujoints full of grease as well as the gimball bearing. Pusing the drive shaft in is a bit like pushing in wet noodle so work it a bit. Once near the coupler you can put a screw drive into the ujoint and trun it a bit to get the slpines to line up. I did it all myself. The drive is a bit heavy but manageble. There are several posts with home made holders if you want to take the time to make one, I hear it is a big help but I didnt need it.

 

[dallas T]

Re: engine overheated

Sounds like instructs to remove the entire outdrive. Pretty strait forward,within my capabilities and inline with what others have posted. <br /><br />I am thinking that it is only the lower gearcase that I need to remove because I want to access the water intake screen. My guess at this point is that the screen is clogged with muck. Or is all of this accessable when I remove the entire unit? Should I drian the oil first or is this not nessecary? <br /><br />So, is it possible to remove the lower gearcase with the outdrive installed on the boat (out of the water)? If so, any special instructions or warings? Should the oil be removed first or is it all contained in the lower gearcase?<br /><br />Thanks again

 

[dallas T]

Re: engine overheated

First of all, thanks for all of the advice so far.<br /><br />Assuming I would need to pull the outdrive off, I went back to the place I bought the impeller kit from to get gaskets etc. The folks there are very friendly so I told them the whole story. They agree that I simply have a clogged screen and suggested that I try to clear it with high pressure water and/or compressed air with the boat in the water. Basically remove the impeller (don't drop the bolts this time) and start back flushing. Sounds reasonable so I will try that first. <br /><br />Thanks,

 

[dallas T]

Re: engine overheated

The story continues...<br /><br />Left the boat in the water and pulled the impeller off. Backflushed the outdrive with compressed air and then garden hose and then more compressed air. Lots of sediment, sand and stuff came out the raw water intake. Re-installed the impeller and removed the 3/4" hose that connects the impeller to the thermostat housing. Fired up the boat and bingo, lots of water pumping from the impeller.<br /><br />Reconnected the hose and ran at idle for 1/2 hour while monistoring the temp. gage. At idle, the temp gage stabilized at 160 degees. Check the flow again and looked good.<br /><br />Took the boat out for a ride and it began to heat up to 190 degrees. Shut the boat down and checked for flow. Still had flow.<br /><br />Limped the boat back to the dock as it was still heating up (200 degrees). Checked for flow again and sure enough still had flow.<br /><br />So now I am puzzled??? Any thoughts as to what would cause it to heat up with good flow?<br /><br />Thanks,

 

[dallas T]

Re: engine overheated

Yet another update...<br /><br />Had the boat owner pull the thermostat despite the warnings of another thread (for this test only). He checked for flow again (good flow) and ran the boat at idle. Temperature sat at 160 degrees (at idle). As soon as he put a small load on it, it went to 180 degrees and he shut it down.<br /><br />Will be picking up a new thermostat on the way home from work but that does not seem to be the root cause. <br /><br />I will check for any sort of blockage after the t-stat but other than that, I am out of ideas???<br /><br />Thanks,

 

[sixysixss]

Re: engine overheated

If it heats up like you say, under load, but not at idle, then it could be a timing issue, or intake or head gaskets.

 

[Don S]

Re: engine overheated

The pump could be putting out plenty of water, but if it doesn't make it out the back, then you have problems. The exhaust manifold ((#23) or elbow (#48)or both could be plugged up. They don't last forever, and if in salt water even less time. May be time to pull the elbow and have a look at the passages.<br /><br />