1998 115 Overheating issue

[batfish1]

Hello Everyone! I have a 1998 S115TXRW Yamaha outboard that the overheating alarm is going off on. I use it mainly in saltwater and flush it after every use. When running at WOT after about 5 minutes the overheat alarm goes off and the engine rpms drop. After turning off the engine and waiting several minutes I ran the motor at around 1500 rpms back to the dock with no alarm going off. I took it to a local boat dealer for service. They tried getting it to overheat in the shop, but were unsuccessful in getting the alarm to go off. They replaced the water pump impeller and water tested it saying it was fixed. I took it back out and it did the same as before for me.

I flushed it with Rydlyme Marine per instructions as shown in this forum by others. I noticed some corrosion in the thermostat area and the thermostats looked pretty corroded. I replaced both Thermostats and gaskets, the pressure control valve, grommet, spring and gasket. Took it back out on the water and the same thing happened as before. Ran it a WOT and after about 5 minutes the alarm went off and rpms dropped. Started it back up and limped back to the dock under 2000 rpms with no alarm sounding.

I ran the motor in a 50 gallon tank at idle between 900 and 1100 rpms for about 30 minutes trying to get the alarm to go off, but it didn't. While running it I took temperatures with a infrared laser thermometer. I took a reading in front of the thermostat and behind. The starboard side read as high as 133 to 136 front and back while the port side read 129 to 133. At the thermo switches the starboard side read 142-146 and the port side read 135-138.

What could be causing the overheat alarm to go off? What should the temperature be at idle speeds between 900 to 1100? Do you think that there is blockage or partial blockage in the water jacket somewhere? I am trying to avoid taking it apart to check the water jackets if possible. I have read in this forum that on older motors the bolts are prone to breaking off. Any advice would be greatly appreciated.

[rodbolt17]

no avoiding it.
after water pump t stats and pressure valve the next step is water jacket and cyl head removal for scraping.

[batfish1]

Thanks Rodbolt! I was afraid that would be the answer.

[rodbolt17]

I do a couple a year on them.
sand pebbles scale , it all builds up.

[Jason2tpa]

btw, you weren't able to replicate the conditions at WOT when you're getting the alarm because when the engine is on flush or in a bucket it is NOT under load. The engine doesn't have to work hard to pump out the same rpms out of the water versus in open water, where it's "pushing" the boat.

The service center obviously tested the engine the exact same way as you did. Otherwise if they had really "water" tested it they have discovered the alarm. Some of these service center folks do the very least amount of work possible to get your buck. Not rodbolt though, no doubt he's one of the few good ones.

[txislandguy]

no avoiding it.
after water pump t stats and pressure valve the next step is water jacket and cyl head removal for scraping.

I have a '98 S200txrw and just finished what Rodbolt said, 1st day back on water today and no overheat alarm.....now if I can only figure out my acceleration delay, but that's a different thread

[TownsendsFJR1300]

For the OP, you'll find major hardened salt in the lower water passages around the cylinder and head.

We did my neighbors 200 a couple of years ago, exact same symptoms.

An FYI, I'd estimate the water passages were easily 90% clogged(especially towards the bottom). It'd only over heat (and shut down into safe mode) at about 4,200 and up. Ran great, to full throttle, after the cleaning.

The rydlyme probably didn't work work for you as it couldn't get into the clogged area.

[99yam40]

Did you drop lower unit ,pull the stats, and hook up a pump and recycle it for a good period of time?
Did you get a lot of junk out of the motor ?
what strength did you use and how long did you recycle the mix

If you still have more of the Rydlyme I would give it one more shot before popping bolts.

Some said they had good results with it

[TownsendsFJR1300]

If you still have more of the Rydlyme I would give it one more shot before popping bolts.

Some links if you need them:

http://www.yamahaoutboardparts.com/f...m-th23666.html

http://www.yamahaoutboardparts.com/f...g-th19434.html

[cpostis]

My two cents...
Stick w/rodbolts "no avoiding it. after water pump t stats and pressure valve the next step is water jacket and cyl head removal for scraping." Otherwise your just delaying the inevitable

I'm just going to show you a few pics of what I found after my first overheat problem (same symptoms as yours).









I also pulled the exhaust cover and plate found excess deposits there as well. I wound up disassembling my whole motor and going through it all. Found the orifices that allow the block to drain totally clogged. I broke a few of the many bolts and had to drill and chase the threads on them. Of course you don't have to do this all, but I would certainly remove head covers, heads, exhaust cover and clean (scrape is the best way).

[TownsendsFJR1300]

My two cents...
Stick w/rodbolts "no avoiding it. after water pump t stats and pressure valve the next step is water jacket and cyl head removal for scraping." Otherwise your just delaying the inevitable

I'm just going to show you a few pics of what I found after my first overheat problem (same symptoms as yours).

Those pic's are exactly what we we encountered but ours was a bit worse...

** I do a thorough flush after every outing, including the muffs and have started using Salt Away for the last 30 seconds of the flush. Just to avoid these issues..

[batfish1]

Many Thanks to Everyone for their input on this thread!! The pictures and links were extremely helpful!

To 99YAM40's question, Yes I did pull the lower unit, remove the T-Stats and ran a 50/50 mix of Marine Rydlime through the water tube for about 3 hours. There was black crud that came out, but not as much as I expected. I will be pulling the head covers next to see what it looks like, but as Rodbolt said I am expecting to find blockage and will be scraping and cleaning for awhile.

[TownsendsFJR1300]

That job, at the shop (locally here, about 3 years ago), would be approx $800.

We did it for a little over $100 in gaskets... No broken bolts either luckily.

[99yam40]

did anyone see in any of the other threads on Rydlyme use see anything about black crud coming out?

[TownsendsFJR1300]

did anyone see in any of the other threads on Rydlyme use see anything about black crud coming out?

I don't remember anything about black crud... Salt build up obviously wouldn't be black as it dissolves...