Water pressure gauge or water temperature gauge?

[brodmann]

If you had room on your dash panel for one more gauge, and you had everything you otherwise needed, which of those would you choose for a 2 stroke?

 

[Scott Danforth]

Water pressure gauge will tell you if you have a problem 2 minutes before the water temp gauge moves

 

[Chris1956]

Water pressure gauge for OBs, especially the inline Mercs which do not have thermostats.

If you watch the pressure gauge, you will know when the impeller is wearing out, by the pressure at a certain RPM. My Johnnyrude will peg the 30PSI gauge at high RPM, when the impeller is new. After a few years, the pressure will be 25PSI, at that RPM.

 

[Texasmark]

I agree that pressure is a faster responder but I wanted to know the t stat and popoff valve were working so I opted for the temp gauge. Not sorry......buttttttt the world of boating has many variables like fishing offshore, so I will agree "different strokes for different folks".....a TV show of long ago.

I agree that there is overlap in usage of whatever sensor you have.

 

[Chris1956]

Gee, Mark, wouldn't you rather know when the engine was starting to overheat, vs after it does? Just a Q...different strokes and all that.

 

[mike_i]

water pressure

 

[Thirsty Endgrain]

Good lord why choose, both.

 

[silverbul]

Gee, Mark, wouldn't you rather know when the engine was starting to overheat, vs after it does? Just a Q...different strokes and all that.

Only if they made these gauges for wives, soon to overheat versus overheating. Definitely number one. lol

 

[brodmann]

Thanks guys. It's for a 115 Yamaha. As I continue to correct an overheating at high RPM problem, I'd like to know it's running hot BEFORE it makes the alarm go off. Seems like that indicates a pretty critical situation. Runs hot when going over 4000 RPM's. I've replaced water pump, Poppit and over the winter, I removed heads and exhaust cover to clean out all passages. There was really very little "gunk" in there. It's had this problem for a while and keeps getting worse. A few years ago, it only ran hot if running at WOT for an extended period of time. Like 20 minutes. Now it's gotten to the point where I can litterally run all day long at 3900 RPM's, but if it bump it up to 4100 RPM's, it will sound the alarm within 2 minutes! I am completely serious! Whe the alarm sounds, I idle down and go into neutral, leaving the motor running. In less than a minute, alarm goes away, ad it is ready to go again. I had about a 45 minute boat ride monday to get to a beach to meet up with my kids and grandkids for the day. I got in a hurry and made the alarm go off a couple of times. The rest of the way there and all the way back, I kept a close eye on the tach, and figured out that I could run forever at 3900 RPM's, but no more. The tell tale never even gets warm. Before saturday, I'll be taking the sensors out and putting them on the stove in a pot of water with the leads hooked up to an ohm meter to determine at what point the send a signal to the alarm. Anyone know what that temperature might be? I've tested the thermostats this way and they seem to open and close at the correct temperature.

 

[Chris1956]

What year is the Yamaha? Some Yamaha's had a tendency for the heads to rot out and leak compression into the cooling system, and vice versa.

Did you replace the thermostat? Can you run at 5000RPM for short periods, or is 4100RPM the max you can get?

A water pressure gauge may help diagnose the issue, especially if you are getting compression into the water jacket.

 

[Texasmark]

Gee, Mark, wouldn't you rather know when the engine was starting to overheat, vs after it does? Just a Q...different strokes and all that.

Well Chris, I am 82 now and my boating experiences are an hour or so every 3 months thereabouts on a local 15k acre local lake. I've had problems with stats and popoffs, my only cooling system problems, and I doubt pressure gauges would have helped.

 

[brodmann]

It's a 1999 S115TLRX. Salt water edition - for whatever that's worth. Now that you mention that, when I bought it, the guy sold it dirt cheap because he took it in for his annual service and there were some water leaks in the top of the #1 and #2 cylinders. The mechanic removed the cylinder heads and soldered it up from the outside and then cleaned out any solder that made it into the water passages. The mechanic is a high school buddy of mine and he told me the boat had very low hours and the guy just didn't flush it after use. He said the repair was sound and should last forever. It hasn't leaked in that area since then and that was 4 years ago. How could I determine If I have a problem like you describe? Over the winter, I removed the cylinder heads and exhaust cover and cleaned out all of the water passages. Nothing really looked too bad. Passages were much cleaner than I expected.

 

[Chris1956]

Possibly a pressure gauge can show high pressure in the cooling water system, from a compression leak. Aluminum in salt water tends to develop ruts and pinholes, over its entire surface. Maybe the original issue has returned in another part of the head?

I have never heard of soldering an aluminum cylinder head. There is aluminum solder, but I never though it strong enough to hold against compression. Have you taken a compression reading recently?

You might price out a cylinder head, just in case.

Mark, unlike inboard/sterndrive engines, which hold cooling water in the block and manifolds, outboards are open systems. It takes a lot to overheat those IB engines, because of the cooling water present at all times. A water temp gauge can therefore show when that water is getting hot.

Outboards self drain, so the water pump must pump enough water to keep the block full, at all times. If the water pressure is too low, the upper part of the engine doesn't cool. Sometimes the water temp gauge is in the upper part of the block, and it can be fooled by lack of water. IL6 outboards are known for overheating on the top cylinder, if the water pump is damaged or worn. A pressure gauge can help the operator see the failure of the cooling system, if you know the pressure at various RPMs.

 

[brodmann]

They did not solder a cylinder head. There were small pinholes on the top of the block in the water jackets. They use some type of solder to seal up the water leaks. No water leaks since then. No water leaking anywhere unless it's internal, but the motor runs perfectly fine and is capable to idling fine through a 20 minute "no wake" zone on either side of my local boat ramp. It's also capable of planing off quickly and reaching 5500 RPM's with no trouble. Obviously, there is some issue causing the high temp alarm to sound. I'll be pulling sensors and thermostats in a pot of water on the stove and checking at what temp the thermostats open, and hooking up ohm meters to sensors to see at what point they are causing the alarm to go off. I'll let y'all know what I find.
Thanks,

 

[3rdtimesthecharm]

Water pressure.

 

[Chris1956]

Yamahas usually have a separate water jacket cover on the head. If you pull that, you can see if there is corrosion on the cylinder head itself.

I am unsure what you meant when you said the pinholes in the water jacket were soldered. Usually, they leak water internally before they leak externally.

My neighbor replaced a Yamaha engine, as the cylinder head rotted thru, allowing water into the cylinder. I never saw that on Mercs or Johnnyrudes.

 

[IslandExplorer]

Sounds like this has been a really tough one to nail down.

Assuming the engine corrosion isn't the culprit (sounds likely tho) and just to throw a completely different idea out there: think it's sucking air at higher speed maybe? I had a boat with a motor that was a touch too high (looked factory) and would barely grab water to the pump on plane. Would slip prop every once in a while in turns too. Maybe test again changing trim and see if any effect. Does the prop ever cavitate in turns or any other indication that the cavitation plate is getting a lot of air under it? Maybe check for bad thru hull up stream feeding turbulence and air bubbles? An open livewell thru hull can drain out and actually blow a bunch of air out the bottom sometimes, Venturi effect. Easy to close it if you have one that's suspect and do same test.

 

[brodmann]

Again, over the winter months, I removed cylinder head covers, cylinder heads and the intake cover to clean out all water passages. There wasn't much in there. I do have a live well that I removed the plug from to use somewhere else. I'll certainly replace that. The height of the motor hasn't changed since It ran fine at WOT without heating issues. The pitting that required soldering caused water leaking to the outside of the motor. Corrosion allowing water to leak into the cylinder would require the corrosion to eat away at the cylinder sleeve! Does that actually happen? Where/how to I look for this corrosion/rotting that you guys are talking about? My son's 90 HP Yamaha had some corrosion that caused him problems, but it made the motor run like crap and one of cylinders was getting a lot of water in it. I'm pretty sure my motor doesn't have that problem, but if you tell me the symptoms and how to diagnose that, I would appreciate it. I'm not opposed to tearing the motor down to look for issues if I know where to look. Wouldn't compression test and/or general overall performance tell me if I have this type of trouble. Motor fires up great and gets up on plane and reaches 5500 RPM's pretty quickly. Jut runs hot if running over 4000 RPM's for a few minutes.
I can't wait to be able to tell you guys what I found the trouble to be.
Thanks for all the ideas.

 

[Texasmark]

Does it have a popoff valve in addition to the tstat for engine coolant regulation? Popoff valves (of which I am familiar) are much larger than stats and are designed to open up at higher water pressures present with increased RPMs and allow additional cooling (without the stat's involvement) at the higher RPMs. If you have no intra-cylinder indication of water intrusion, might replace your popoff valve and try again.

 

[brodmann]

As stated in #9, it's been replaced. Replaced with the new "mushroom" style and grommit was replaced also.
Thanks for your reply.