What is the pressure reading on a Johnson 70 hp

[ritamigo]

Just installed the gauge and I am getting a 10 reading at 4.500 rpm is taht normal?

Thanks,

JoeVee

 

[Tim Frank]

Re: What is the pressure reading on a Johnson 70 hp

Just installed the gauge and I am getting a 10 reading at 4.500 rpm is taht normal?

Thanks,

JoeVee

It would depend a lot on which pressure you are measuring, water, fuel, oil etc.

 

[ritamigo]

Re: What is the pressure reading on a Johnson 70 hp

Sorry at would be water pressure. The motor is a 1994 model J70TLERC.

Thanks...

 

[Haffiman]

Re: What is the pressure reading on a Johnson 70 hp

I would expect a max reading closer to 20PSI around 2500-3000 rpm. When did you last change impeller?

 

[ritamigo]

Re: What is the pressure reading on a Johnson 70 hp

I would expect a max reading closer to 20PSI around 2500-3000 rpm. When did you last change impeller?

I never have, just got the boat about 4 months ago. Where is the impeller and is it difficult to change. I have restored cars, so i can do it.

Thanks again...

 

[Haffiman]

Re: What is the pressure reading on a Johnson 70 hp

disconnect the shift-rod from link (under the carbs), drop the lower unit.

 

[Silvertip]

Re: What is the pressure reading on a Johnson 70 hp

Do yourself a big favor and buy a service manual for your specific engine. The idea of adding a water pressure gauge is to install a new impeller at the same time. You then note the idle, mid range and wide open throttle pressures. Any deviation down the road indicates the impeller needs attention. So until you install a new impeller, you don't know what is good or not.

 

[ritamigo]

Re: What is the pressure reading on a Johnson 70 hp

Do yourself a big favor and buy a service manual for your specific engine. The idea of adding a water pressure gauge is to install a new impeller at the same time. You then note the idle, mid range and wide open throttle pressures. Any deviation down the road indicates the impeller needs attention. So until you install a new impeller, you don't know what is good or not.

Thanks makes sense. I just ordered one. Good answer. So all being good it should be about 20-25 at 5000 RPM?

JV

 

[Tim Frank]

Re: What is the pressure reading on a Johnson 70 hp

Thanks makes sense. I just ordered one. Good answer. So all being good it should be about 20-25 at 5000 RPM?

JV

Maybe, but the point is that you are not so much looking for an absolute reading value as you are looking for a baseline for your engine.
New impeller, good stream, and check the reading as ST said..
You now have a reference point and will have advance warning of deterioration of the cooling system.

In fact, one of the targets of any gauge (usually...) should be to have a "normal" reading at about 1/2 full scale deflection....so that is another way of looking at it.

 

[NoEcm]

Re: What is the pressure reading on a Johnson 70 hp

1988 70hp Johnson J70ELCCA purchased new.

When purchased new (and after an impeller change):
6psi @ idle
18psi @ WOT

 

[ritamigo]

Re: What is the pressure reading on a Johnson 70 hp

1988 70hp Johnson J70ELCCA purchased new.

When purchased new (and after an impeller change):
6psi @ idle
18psi @ WOT

Thanks all.... appreciate the input.

JV

 

[Haffiman]

Re: What is the pressure reading on a Johnson 70 hp

The max psi should be reached long before max WOT rpm as I mentioned earlier. The opening pressure of the by-pass valve is around 20PSI if remembering correct. The way to 'use the system is to notice when you need to increase your rpm to obtain that pressure. if rpm need to be increased around 10% from new impeller, change impeller! The pressure is not a given fix value as it might vary due to trim and installation as well as boat speed. In some cases you might need a higher rpm, in other a lower to obtain the opening pressure.

 

[ritamigo]

Re: What is the pressure reading on a Johnson 70 hp

The max psi should be reached long before max WOT rpm as I mentioned earlier. The opening pressure of the by-pass valve is around 20PSI if remembering correct. The way to 'use the system is to notice when you need to increase your rpm to obtain that pressure. if rpm need to be increased around 10% from new impeller, change impeller! The pressure is not a given fix value as it might vary due to trim and installation as well as boat speed. In some cases you might need a higher rpm, in other a lower to obtain the opening pressure.

Thanks. 2 quick questions:

1-Should I and can i install a water temperature gauge? And where does the sender go?
2-What is the maximum RPM and is there a shut-off to avoid engine damage? (Johnson 1994 J70TLERC)

Your answer is great. Thanks again!

JoeVee

 

[Haffiman]

Re: What is the pressure reading on a Johnson 70 hp

1: There are temp gauge kits available. They mostly use a surface-contact sender attached to the head with a bracket. Search 'accessories' at shop.evinrude.com for your and/or earlier year.
2: If not mistaken, your powerpack has a RPM limiter, but not quite sure of the setting.

 

[Haffiman]

Re: What is the pressure reading on a Johnson 70 hp

1: There are temp gauge kits available. They mostly use a surface-contact sender attached to the head with a bracket. Search 'accessories' at shop.evinrude.com for your and/or earlier year.
2: If not mistaken, your powerpack has a RPM limiter, but not quite sure of the setting.

 

[ritamigo]

Re: What is the pressure reading on a Johnson 70 hp

1: There are temp gauge kits available. They mostly use a surface-contact sender attached to the head with a bracket. Search 'accessories' at shop.evinrude.com for your and/or earlier year.
2: If not mistaken, your powerpack has a RPM limiter, but not quite sure of the setting.

Thanks... how can I be sure it has a RPM limiter? I purchased the manual, will that have the info? If not, how can i verify it?
Thanks again...

JoeVee

 

[Haffiman]

Re: What is the pressure reading on a Johnson 70 hp

It is a bit of a jungle. Go here:
http://bpi.ebasicpower.com/c/OB-OMCPP/Power+Packs/RPMs/Limiters+for+Johnson+Evinrude+Outboard

Most of them follows the standard original powerpacks, and as you may see, some has - some has not. cross check with the replacement number on the pack you have.

 

[ritamigo]

Re: What is the pressure reading on a Johnson 70 hp

It is a bit of a jungle. Go here:
http://bpi.ebasicpower.com/c/OB-OMCPP/Power+Packs/RPMs/Limiters+for+Johnson+Evinrude+Outboard

Most of them follows the standard original powerpacks, and as you may see, some has - some has not. cross check with the replacement number on the pack you have.

Thanks again.....

JoeVee