1986 Yamaha 90 ETLK cooling flow problem

[guerryb]

I recently picked up a 1986 17 Striper with a 1987 Yamaha 90 ETLK. I do not get water from the tell tale and the engine quickly gets hot. Apparently the previous owner was neglectful with proper flushing, or the engine is simply so old that it has excessive corrosion on the all over.

The engine has a brand new head with poppets, thermostat, and water pump. Before cranking the engine for the first time, I inspected it thoroughly and performed a compression check revealing 125-PSI on all three [cylinders] when the engine is stone cold. All looks good, it starts easily and runs smoothly.

I noticed no water out from the tell tale and started investigating. With ear muffs, it never pushed water up and out of the tell tale. I pulled the thermo cover and found a small amount of crustiness. I cleaned that out and reinstalled them but no water ever came from the tell tale when running at any RPM.

I removed the thermostat cover and ran the engine with it off. Water pushed out the top with the foot in a barrel of water and no water hose pressure. Assuming I did not get the pump primed at first, I reassembled the thermostat section and cranked it again. No water.

Assuming there were blockages in other areas, I did the salt-away process by pouring it thru the thermostat hole and running the engine briefly to push any debris out the top. The cleaning solution flowed out through the foot and did not seem to find any restrictions. While apart, I tested the thermostat in a pot on the stove. It started opening at approximately 160-degrees. The thermostat is shiny brass and appears to be new. The poppet valve and O-ring appear new too.

I reassembled again and no luck. With the thermostat installed I get no flow out the tell tale and the engine quickly gets hot. I don't let [the engine heat rise to the level that would sound an] alarm. I just use a laser thermometer and read the heads near the plugs, and I shut off the engine if the readings on the thermometer approached 180-degrees externally. With the thermostat OUT, the temperatures all over the head and exhaust plate on the side are very cool, never reaching 100-degrees. I assume inside temperatures are getting hot, but not reaching dangerous levels. Also, water ALWAYS flows out the front water return hole on the foot regardless of thermostate in or out.

Any ideas why I see no tell tale water and it gets hot quickly? Why no flow with the thermostat installed and plenty of flow with it removed but the cover is installed? If the thermo is normally closed, I should still have tell tale water flowing, right? Any help will be most appreciated!

[jimh]

I used to own twin 1987 Yamaha three-cylinder 70-HP engines. The only time I experienced a loss of water flow from the confidence stream nozzle (or tell tale), I was able to remedy the problem by cleaning out debris that was blocking flow to the nozzle. Some mud or perhaps a mud wasp had gotten into the hose.

I didn't see a mention in your narrative of steps taken that included cleaning the nozzle and any hoses feeding it. I don't have the service manual for your engine, so I can't verify this speculation: perhaps the feed to the confidence stream nozzle is also the VENT for the cooling system. If there is blockage then the cooling system cannot vent out air and bleed itself. This could be related to the overheating. Thus a blockage like I propose could cause both symptoms.

[guerryb]

The nozzle and hose aren't clogged as the water passes freely through it when the thermostat is removed. However the rubber hose that the nozzle connects to connects to the engine at the lowest part of the exhaust plate on the side of the cylinders. Because it's at the bottom, I assume it's possible for water to make it to the bottom of the motor and flow back down the tell tale without making it to the thermostat at the top.

I wish there was a map of the water flow paths in the engine. It just doesn't make sense that removing the thermostat allows water to make it to the tell tale.

[jimh]

If the hose feeding the confidence stream nozzle is not at the highest point in the cooling system, then it probably is not functioning as a vent; my speculation was probably wrong.

Although you describe the water pump condition as "new", you may want to investigate the water pump. Perhaps when it was serviced it was not properly installed. The water pump may be having trouble lifting water to the top of the engine or it may not be providing enough pressure in the cooling system to activate certain pressure-sensitive valves. These pressure sensitive valves are forced open by the pressure of the cooling water system and add much additional cooling to the engine, usually when the throttle is advanced and engine speed increases. In some engines these valves are not pressure-operated but instead are mechanically linked to the throttle arm. Again, without the service manual here I cannot tell how that Yamaha is designed.

[Jefecinco]

Generally if a pump will not lift unless primed (lower unit in a barrel of water) the pump is not functioning at full capacity. Are you certain a new water pump kit was installed? Many water pumps have a wear plate above and or below the impeller. Most full pump repair kits include any wear plates but stand alone impellers are available. It's possible that only a new impeller was installed on your engine when a kit was needed. It's possible to install an impeller upside down in some pumps, but because your pump seems to function well when primed that seems unlikely.

Regardless, I believe your next step may be to inspect the water pump.

[guerryb]

Many thanks for all the advice. As of today it seems to be working properly.

Currently I think the problem was caused by an excessive amount of scale build up in the exhaust baffle section. A new head assembly and water pump were just installed, but the exhaust baffle did not appear to have been removed for service. After reading in many other threads, I too chose to not attempt the baffle removal since it seems everyone else had catastrophic numbers of bolts ring off.

I flushed the upper cooling channels several more times. I alternated between distilled cleaning vinegar and "Dollar tree" admirable CLR cleaner. Each time I added cleaner to the system, I would have the motor tilted all the way up so the fluid would stay up in the motor section and not run back out the foot.

After allowing the cleaner to sit for about 30 mins, I dropped the motor back down into the water barrel and ran the motor for about 3-5 mins with the thermostat cover off. With the cover off, the foot in a water barrel, and ear muffs on with full water hose pressure, a full and fast flow of water pushed out of the thermostat and poppet holes. Any lose scaling was pushed out the top. Any dissolved salt or scaling would also flow out of the motor this way, and not go into the other coolant water passages in the head and baffle.

I've cranked the motor (cold) a half dozen times or more since it started working again. Every time it starts and quickly delivers a strong stream from the Tell Tale. next step is an all telling sea trial!

In the future, I'll do a vinegar / CLR flush periodically to make sure the flow paths are not hindered. I plan on stocking up on $1 a gallon "distilled cleaning vinegar" to clean the cooling passages as I flush from a barrel. Hopefully this one has many more years to give.

[mtown]

I own a 1989 90 HP and keep a small strand of copper rigging wire in my tool kit as it seems that some very small creature has always built a mud dam in the pee hole.

A simple trick I learned to test the water pump and impeller is.

Put muffs on motor. Turn hose on SLOW. Have some one crank motor to start while you watch muffs.
If muffs suck inward the pump/ impeller are working.