1999 150 overheating problem

[BuilderBob]

Hi all. First post. Looking for some help.

Ok, I admit it. I made a dumbass mistake and started my motor without the water being turned on at the muffs. I realized my mistake pretty quickly and turned on the water. Everything was fine and the telltale was shooting a solid stream as expected. Ran the engine for 15 minutes with no problem.

A couple of weeks later, I started the motor again, this time with the water on, and I got nothing from the telltale. Soon the overheat alarm sounded and I shut her down.

Replaced the complete water pump assembly last weekend (the impeller was toast, wear plate was scored, etc) and made sure that the cooling pipe that connects to the water pump was free of debris by running a coat hanger up the tube. Reassembled everything, put the muffs on, turned on the water and started the engine.

Initially, there was water at the telltale, but it soon stopped and the overheat alarm sounded again. I immediately shut it down.

Decided to check the T-stats on the cylinder heads. Figured that could be a place where debris might accumulate. Pulled 'em, checked 'em. No debris.

Put it back together and started the motor. This time I did get a weak stream at the telltale, but the overheat alarm soon sounded again, so I shut her down.

I'm going to pull the pressure control valve today to see if it is stuck open.

My guess is that some of the impeller debris went up into the engine and plugged something up, but I have no idea of where to look or where debris might accumulate if it gets up that far. Hoping for some advice from forum members.

The motor is a 1999 Yamaha 150 2-stroke. No oil injection.

Thanks in advance for your help!

[TownsendsFJR1300]

Worse case scenerio (but please wait until others chime in) is to pull the heads.

The sensors are either there or close to there.

Sounds like, as you stated, crap got up there and is blocking that coolant passage setting off the alarm..

I'm wonder if if you can flush from the poppit valve (if its lower) with the thermostats out and flush it out and upwards..

Good luck...

[BuilderBob]

Worse case scenerio (but please wait until others chime in) is to pull the heads.

The sensors are either there or close to there.

Sounds like, as you stated, crap got up there and is blocking that coolant passage setting off the alarm..

I'm wonder if if you can flush from the poppit valve (if its lower) with the thermostats out and flush it out and upwards..

Good luck...

Thanks for response. I certainly hope I don't have to pull the heads, but if I do, let it be a lesson to others to ALWAYS have the water on at the muffs! LOL

[BuilderBob]

Changed the T-stats and pressure relief valve today. Started her up (with water at the muffs ) and let her run at about 1,100 rpm. Telltale was working as good as it did before burning up the impeller. After about 2 1/2 minutes the overheat alarm sounded. Turned it off.

I put my hand on the cylinders and heads to see if they were hot. Definitely not too hot to touch, but I wouldn't leave my hand on there. On the right side bank (looking from the rear), the top cylinder was hotter than the lower.

Trying to eliminate all of the possibilities before concluding that the heads must be pulled. Is it possible that water could still get to the power head if the water tube wasn't inserted into the pump housing? I wasn't checking that alignment when I reinstalled the lower unit. I guess my next step will be to pull the lower unit and confirm that everything is still ok down there and that the water pipe is fully seated in the pump housing.

Still looking for guidance.

[TownsendsFJR1300]

I have to doubt the water pipe came out (I don't know for certain) however re-checking it can't hurt. You may get some crap come out while doing so too.

BTW, do you have an idea how much material is still missing from the torn up impeller?


If you access to a lazer temp gun, (a new, decent one, is about $60), it could be in-valuable in narrowing down where on the block/head its the worst(hottest) and help you to just work in that area/head.

I'm not sure if the auto parts store has them under their tool loaner program.

I use mine all the time and used it on my brothers, little, old Evinrude when it was having water flow issues. I could tell immediatly when the water wasn't flowing correctly and when it was. We did eventually get out what ever crap was in there..

Also, some engines don't like to run strictly on muffs for any lenth of time. If you've been flushing before without issue on muffs, disreguard..

[BuilderBob]

If you access to a lazer temp gun, (a new, decent one, is about $60), it could be in-valuable in narrowing down where on the block/head its the worst(hottest) and help you to just work in that area/head.

I'm not sure if the auto parts store has them under their tool loaner program.

I use mine all the time and used it on my brothers, little, old Evinrude when it was having water flow issues. I could tell immediatly when the water wasn't flowing correctly and when it was. We did eventually get out what ever crap was in there.. [/B]

Well, I guess the day isn't a total loss if I have an excuse to buy a new tool.

Just checked. Infrared thermometer with laser pointer $35 at Harbor Freight. I think I might even have a 20% off coupon hanging around here somewhere too!

[TownsendsFJR1300]

Well, I guess the day isn't a total loss if I have an excuse to buy a new tool.

Just checked. Infrared thermometer with laser pointer $35 at Harbor Freight. I think I might even have a 20% off coupon hanging around here somewhere too!

I would just, in the store check how accurate it is.

I have the Raytec MT6(Below link), its another name for a double the price, EXACT SAME unit(forgot the name). Extremly accurate..

Amazon.com: Raytek MT6 Non-contact MiniTemp Infrared Thermometer: Automotive

[BuilderBob]

I would just, in the store check how accurate it is.

I have the Raytec MT6(Below link), its another name for a double the price, EXACT SAME unit(forgot the name). Extremly accurate..

Amazon.com: Raytek MT6 Non-contact MiniTemp Infrared Thermometer: Automotive

Looks nice. The Raytec specs put it at .5% more accurate than the Harbor Freight unit. For my purposes, I think the HF unit will be ok. It should certainly detect a difference in temps between upper and lower cylinders.

Cent-tech Thermometer

[BuilderBob]

Took the day off to mess with the cooling system some more today.

First, filled this tub and kept a hose running in it while the engine was running so that it would have a constant supply of fresh water. Water level was way over the intake.



Started the motor and let it run for about 10 minutes at about 1,200 rpm. Periodically checked cylinder head temp with the touchless infrared thermometer that I picked up at Harbor Freight. Lower cylinders were cooler, at about 128 and the upper cylinders were hotter at about 135. Overheat alarm didn't sound and there was a strong stream at the telltale.

Then I decided to back the throttle down to idle and let it run a while longer. Telltale was still present, but not nearly as strong and the alarm sounded after about 5 minutes. Shut her down.

Check the head temps again. Left cylinder bank (looking from the rear) was up to about 150, but the right bank was up to about 182. Obviously, the right bank has more blockage than the left, but I don't know if 150 degrees is within the normal range for the left bank.

I have a couple of water jacket gaskets on order. Should be here tomorrow. After the motor cools off, I'll go out and pull both of the water jacket covers and report what I find.

[DennisG01]

It was mentioned above, but you NEED to find all of the missing impeller pieces. Overheating issues have plagued many, many people (including me)... until you find the missing pieces and then all is well again. It can be a real pain, but it's important.

[BuilderBob]

I think I found the problem.

After pulling the water jacket covers and discovering no impeller debris and that they were reasonably clean for an engine this old, I decided to pull the lower unit again to check the pump.

Long story short, I forgot to transfer the grommet that seals the pump housing to the water tube from the old pump housing to the new one. Doh!

Because I pulled the water jacket covers and have to wait for new gaskets to reinstall, I can't say for 100% certain that the issue is resolved, but it makes sense that if the water tube wasn't sealed to the pump, that would be my problem right there.

Damn! I need to find a better mechanic. My current one sucks!

[TownsendsFJR1300]

At least you found it before pulling heads!!!

Do you think you have all the parts from the impellor?

Can you get the nozzle of an air compressor to blow down behind the jacket covers?

I'd be concerned about debris in and about the cylinder water jackets (under the head). Thats where most of salt build up occurs(not in this case)

[BuilderBob]

Yes, I'm pretty sure there is no impeller debris in there. When I removed the old one, it hadn't lost any "chunks", it just kind of disintegrated into fine bits which clogged the outlet of the pump housing.

Before I reinstall the head covers, I'll get a wire brush (brass) and knock down what little salt buildup and corrosion that there is in there. I'm anticipating a complete recovery!

Really appreciate your help!

BTW, I'm a former FJR owner. Great bike!

[TownsendsFJR1300]

BTW, I'm a former FJR owner. Great bike!

Exellent, please post your final outcome (sounds like you have it figured out).



BTW, My FJR was an 04, the first, (very HOT) Gen I bike. I sold it a couple of years ago, just too hot for southern Florida. Loved the bike, just couldn't ride it for half the year with the heat!

I usually rode W/O the bags, here it is loaded for a road trip.

[DennisG01]

Good luck, Bob. I hope you've got things figured out! Sounds like you do.