# Yamaha 70 Water Pressure



## JoshJ

It's gonna be hi pressure low volume on that motor. 20 -30 wot is about right.


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## Smackdaddy53

JoshJ said:


> It's gonna be hi pressure low volume on that motor. 20 -30 wot is about right.


I figured so because if my memory serves me all the Yamahas I have run on other guy's boats were over 20psi. Thanks.


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## JoshJ

I was a Yamaha mechanic in a past life. I am very familiar with the older carbed 2 strokes. I got out of it in the early 2000's so all the new fuel injection 4 stroke stuff is new to me. I have a 250 sho on a Majek xreame and it is a high volume low pressure system. I was surprised when I first got it and was only seeing 15 pounds wot. The 60 four stroke that I just picked up on the hpxt seems to be a high pressure system but it doesn't have a gauge either. I will be adding a gauge if I decide to go with a jackplate.


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## Smackdaddy53

JoshJ said:


> I was a Yamaha mechanic in a past life. I am very familiar with the older carbed 2 strokes. I got out of it in the early 2000's so all the new fuel injection 4 stroke stuff is new to me. I have a 250 sho on a Majek xreame and it is a high volume low pressure system. I was surprised when I first got it and was only seeing 15 pounds wot. The 60 four stroke that I just picked up on the hpxt seems to be a high pressure system but it doesn't have a gauge either. I will be adding a gauge if I decide to go with a jackplate.


Well I finally got the boat on the water yeaterday after having a new prop custom made for her and adding a compression plate and I am very happy EXCEPT it overheated a couple of times at WOT. I got it home and took the thermostat cover off and freaked out at the amount of corrosion on it. They previous owner swore he flushed it every trip but I beg to differ...I decided to go ahead and buy all the gaskets to clean the entire cooling system including the water pump. I still have to replace the water pump tomorrow but I got the powerhead cleaned out and everything flushed out today. It was really ridiculous how much salt was built up on the water jackets. I used Starbrite Bottom Cleaner to break the crap up and rinse it away. It was recommended to me by my buddy at the local Yamaha shop and worked great.
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## Tx_Whipray

how many bolts did you break off in the block? If the number is less than 3 you are a gotdang magician.


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## EdK13

Tx_Whipray said:


> how many bolts did you break off in the block? If the number is less than 3 you are a gotdang magician.


He is something else. Just figures stuff out. No Fear.


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## Smackdaddy53

Tx_Whipray said:


> how many bolts did you break off in the block? If the number is less than 3 you are a gotdang magician.


Zero, not my first rodeo! ALWAYS heat them up with a mini torch a few times and let them cool between so the bolt expands and contracts and it breaks up the corrosion on the threads. Loosen with a wrench then finish with an impact.


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## Smackdaddy53

I got the water pump housing off and the lower cast aluminum piece broke in half so I have to buy that tomorrow. I am going to replace the lower unit lube tomorrow as well and drop her off at the shop to have my platform fabbed after I take a test drive.


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## EdK13

Smackdaddy53 said:


> I got the water pump housing off and the lower cast aluminum piece broke in half so I have to buy that tomorrow. I am going to replace the lower unit lube tomorrow as well and drop her off at the shop to have my platform fabbed after I take a test drive.


Try to land a Red or something ... on your "Test Drive" s/


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## JoshJ

That cleaned up really nice. That was most likely caused by sitting up. I have seen motors salt up with 50 hrs on them that were flushed, but only run twice a year. On the other hand, we would have crab boats that were never flushed with over 2000 hrs and were spotless inside.


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## lemaymiami

Two thoughts... I won't rig a skiff without a water pressure gauge, period (I think they're that important - particularly if you run at night....). 

Motors, in the salt, need to be run regularly (none of that use it once or twice then let it sit for months before additional use, way some folks do....). Anyone finding a "bargain" with a three or four year old motor with very, very few hours on it is actually picking up something that will keep their mechanic's rent paid - on a regular basis...


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## Smackdaddy53

lemaymiami said:


> Two thoughts... I won't rig a skiff without a water pressure gauge, period (I think they're that important - particularly if you run at night....).
> 
> Motors, in the salt, need to be run regularly (none of that use it once or twice then let it sit for months before additional use, way some folks do....). Anyone finding a "bargain" with a three or four year old motor with very, very few hours on it is actually picking up something that will keep their mechanic's rent paid - on a regular basis...


I am with you on this. I am taking a break right now from finishing the complete cooling system cleaning and replaced the entire water pump all the way to the gear case. Finished that this morning and now installing a Yamaha water pressure gauge and new fuel sending unit and wiring. I don't mind working on my boat, it gets me familiar with my vessel so I can take care of my own issues if they arise. I'm ready to fish!
She will be run quite often even if it is on the hose while I drink a couple of brews. I am a big believer in flushing with the Salt Terminator system, it is what my guide buddies use and it is great for the cooling system.


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## Tilly_Copano

I just bought an 03 Maverick HPX- T with the same motor. I want to add a water pressure gauge and would really like to replace the current gauges , the speedometer doesn't work, and replace the switch panel. Can you give me an idea on how hard is this to do? I have to experience but really want to start doing these kind of things myself.


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## Smackdaddy53

Tilly_Copano said:


> I just bought an 03 Maverick HPX- T with the same motor. I want to add a water pressure gauge and would really like to replace the current gauges , the speedometer doesn't work, and replace the switch panel. Can you give me an idea on how hard is this to do? I have to experience but really want to start doing these kind of things myself.


Screw the speedo if you have the same multifunction Yamaha gauges I have because they run off pressure. If you have a GPS just use that.
The Yamaha water pressure gauge is simple to install, drill a 2 1/16" hole and run the Yamaha hose with fitting that taps into the plug by the thermostat and wire the lights to the existing lights on the other gauges.
I have not started replacing the switches but when I do it will probably be a prewired Blue Seas switch panel to save time and they are pretty slick.


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## sjrobin

Nice work on the Yam 70. More important than the water pressure gauge is the hot horn buzzer function / rpm reduction. Make sure the over heat protection system functions. Turtle grass, plastic bags, etc can smoke your power head in less than a minute, while your focusing on the horizon, looking at a GPS screen, or talking to your girlfriend.


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## Smackdaddy53

sjrobin said:


> Nice work on the Yam 70. More important than the water pressure gauge is the hot horn buzzer function / rpm reduction. Make sure the over heat protection system functions. Turtle grass, plastic bags, etc can smoke your power head in less than a minute, while your focusing on the horizon, looking at a GPS screen, or talking to your girlfriend.


Hot horn and check the oil pump linkage because I was getting an oil alarm and noticed the little threaded nylon knuckle that links the throttle to the oil pump was split and not connected. Thank God the Japanese made it automatically go into over oil mode if this happens. Also check the other side where the computer is and the throttle links up to that with a little nylon knuckle. Mine was split as well.


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## JoshJ

Tilly_Copano said:


> I just bought an 03 Maverick HPX- T with the same motor. I want to add a water pressure gauge and would really like to replace the current gauges , the speedometer doesn't work, and replace the switch panel. Can you give me an idea on how hard is this to do? I have to experience but really want to start doing these kind of things myself.



What Mac said on the water pressure gauge.

The Multi Function gauges are easy to replace, all of the wiring is just plug and play. As far as the inop speedo, check the hole in the front of the lower unit to make sure it is not plugged up. You can clean it out with a piece of wire or turn a small drill bit in it BY HAND.


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## Smackdaddy53

JoshJ said:


> What Mac said on the water pressure gauge.
> 
> The Multi Function gauges are easy to replace, all of the wiring is just plug and play. As far as the inop speedo, check the hole in the front of the lower unit to make sure it is not plugged up. You can clean it out with a piece of wire or turn a small drill bit in it BY HAND.


I need to clean mine out while the lower unit is off and run some stiffer tubing that won't get pinched. It is kind of redundant having the speedometer on the GPS as well but I want everything to work!


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## Smackdaddy53

I broke my shifter bracket while trying to get my lower unit back on. Don't ever do this! I didn't realize my shift shaft splines weren't lined up with my lower unit and broke the arm under the powerhead. I had the powerhead completely removed in an hour and fifteen minutes, it wasn't hard at all like the guy at the Yamaha shop said it would be. The up side is I got to clean my lower cowling and check all my electrical connections and gasket between my powerhead and midsection. The bracket has been overnighted so I should have it some time next week...haha

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## Smackdaddy53

Back on and buttoned up, it wasn't hard at all. 

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## JoshJ

Damn, Your gonna have a new boat when you're done.


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## Smackdaddy53

Just ran it and everything checks out. I'm going to run wires to the water pressure gauge and refill my Seastar system since I replaced both hoses Friday. $24 a quart for "special" hydraulic fluid is ridamndiculous.


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## robwill54

Toilet bowl cleaner takes out that corrosion pretty fast and easy. 

Bob


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## not2shabby

This was a serious project, Mac. I need to do some cooling system cleaning myself. I'm afraid I've got some buildup and overheated for the first time last week. Thanks for the photos and how-to. Good chance I'll be calling you when I get to this point!


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## Smackdaddy53

not2shabby said:


> This was a serious project, Mac. I need to do some cooling system cleaning myself. I'm afraid I've got some buildup and overheated for the first time last week. Thanks for the photos and how-to. Good chance I'll be calling you when I get to this point!


We can lift the powerhead by hand if both of us are present. Let me know when you are ready and I’ll give you a hand.


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## Smackdaddy53

Oh and the water pressure gauge was a waste of $100 and a hole in the console. That motor put out a couple of psi at best, high volume low pressure.


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## not2shabby

I already have a pressure gauge. It shows almost imperceptible pressure at idle and about 8psi running. 

Definitely need to think about timing for the project. Probably winter, I would guess.

Did you ever consider removing the thermostat? I’ve read lots of different opinions on that.


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## Smackdaddy53

not2shabby said:


> I already have a pressure gauge. It shows almost imperceptible pressure at idle and about 8psi running.
> 
> Definitely need to think about timing for the project. Probably winter, I would guess.
> 
> Did you ever consider removing the thermostat? I’ve read lots of different opinions on that.


That’s not even smart, your powerhead needs heat to run correctly. If you remove the thermostat you will allow the water to just piss right back out and the powerhead will run too cool and you’ll be having seized pistons and all kinds of engine trouble in the near future. The same applies for a vehicle motor, you need that designed head temperature or it screws up the tolerances between the pistons and cylinder walls. The phrase “let the motor warm up” is exactly what it reads.


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## commtrd

Fueling algorithms also will be seriously negatively affected if the powerhead (or my cummins 5.9) runs too far out of the temperature range the computer is looking for. Temperature regulation is critical for modern engines.


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## Smackdaddy53

I have heard many people say they will remove their thermostat(s) in the summer because the water is so hot it doesn’t matter but average powerhead temperature is around 145-148 degrees and your powerhead can’t heat 88 degree bay water that fast before it makes it back out of the system. 
I know that if you break in a brand new motor or freshly rebuilt motor you have to let it warm up completely before you take off from the ramp or the pistons will score the cylinder walls because the metal has not expanded enough yet. The block will take longer to heat up than the pistons because it’s a bigger chunk of metal. If you have a head re-sleeved and take off prematurely the piston will grab the sleeved cylinder and move it. I always crank my motor as soon as I get it backed in the ramp and let it idle a while and even then I’ll idle out in gear a while in the cooler months.


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## Guest

Smackdaddy53 is dead on! If you like The idea of premature catastrophic engine failure then by all means pull the t stats. If you want your motor to last as long as it can then leave them in and allow to warm up and cool down as it was designed to do.
Commtrd is also correct in that a cool running engine no matter 2/4 stroke, gas, diesel is not going to run efficient.


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## not2shabby

Can’t argue with that. It’s 16 years old and runs like a top. No need to change anything.

I pulled off the tell tale hose and fitting, blew it out with compressed air, ran a pipe cleaner through it, and cleared out the male fitting on the powerhead. I also drilled out the tell tale fitting an extra 1/16th. Now it flows like a super soaker. Very happy.

I got my first overheat alarm two weeks ago because I raised the motor up all the way on the bolt holes and then ran it jacked up to 6. I must have lost water pressure and over heated. Two responses: fix tell tail so I can actually see when I’m losing flow and add transport cav plate to help keep water on the intakes when I jack it up. Step one done. Step two maybe next weekend.


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## ek02

On the subject of water pressure, it depends where you tap into the engine. Most Yamahas have a plug where the fitting needs to go. If you T into the P tube, water pressure will be very low. My Yamaha 90 2 stroke will have 19 PSI cold tapped into the factory plug. The warmer the water, the lower the water pressure because the thermostat will open more. The 90 has a spring loaded thermostat by pass valve and in really warm water the pressure will be 12-15 PSI. The thermostat always looks new. We also have a F40 on another boat and it has no bypass. All water goes through the thermostat. It gets plugged up and has to be replaced yearly. The water pressure is usually 25-30 PSI on that engine. I carry a spare gasket for the 40 in case the thermostat plugs up so I can remove it and get home. Always run a thermostat in any engine. This ain't the 50's, when we never ran them in our cars in S Florida.


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## Smackdaddy53

ek02 said:


> On the subject of water pressure, it depends where you tap into the engine. Most Yamahas have a plug where the fitting needs to go. If you T into the P tube, water pressure will be very low. My Yamaha 90 2 stroke will have 19 PSI cold tapped into the factory plug. The warmer the water, the lower the water pressure because the thermostat will open more. The 90 has a spring loaded thermostat by pass valve and in really warm water the pressure will be 12-15 PSI. The thermostat always looks new. We also have a F40 on another boat and it has no bypass. All water goes through the thermostat. It gets plugged up and has to be replaced yearly. The water pressure is usually 25-30 PSI on that engine. I carry a spare gasket for the 40 in case the thermostat plugs up so I can remove it and get home. Always run a thermostat in any engine. This ain't the 50's, when we never ran them in our cars in S Florida.


Your 90 is a high pressure low volume motor, the 70 I have is a low pressure high volume system. I have my pressure gauge installed with a Yamaha water pressure kit that included the fitting that threads into the factory water pressure port on the top left rear of the head. I believe I need a gauge with 10psi in one psi increments instead of a 30psi with 5psi increments.


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## jimsmicro

I have the same motor. They're easy to work on and reliable, one of my favorite outboards I've owned so far. If you had that much corrosion there you may also have problems with the exhaust housing area as well. Yamaha didn't do too great with using any sort of anti-seize on these motors it seems to me. The bolts will fight you and if you're ham fished stuff will break off with a quickness. You had the right idea, heat, oil, and removing by hand. An impact is asking for trouble.


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