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Installing a water pressure gauge

T

taymag

Contributing Member
How hard is it to install? And since Mercury/quicksilver doesn't make one, is there a quality brand recommended?

And if I dont want to run it to my dash can I just mount it back in the bulge and look at it every once in a while instead?
 
If that tube was there from factory I would suspect that it's the feed tube coming up from the integral pitot tube in the lower unit which is used to feed a speedometer (which works on pressure).

While I don't work on or even see many Merc's with more than two cylinders, your plug location for a water pressure sensor may be where I have put the yellow arrow - just below the bottom coil on the right hand side of the head, from the perspective of standing behind the motor.
 

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That's the coil mounting plate bolt marked with arrow.....That hose if it comes off the bottom adapter plate on a warer fitting that's your pressure hose which it should be. Use the Merckit 79-895288A04 as it 30psi and the A01 is 15 psi for inline motors.
 
faztbullet said:
That's the coil mounting plate bolt marked with arrow.....That hose if it comes off the bottom adapter plate on a warer fitting that's your pressure hose which it should be. Use the Merckit 79-895288A04 as it 30psi and the A01 is 15 psi for inline motors.
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Ok appreciate the help, so how do I use that brown tube with the red tab with the merckit you suggest?
 
Push in on ring on connector and pull the red plug out...then slide hose into connector. Just like a sharkbite fitting
 
Ive never used a water pressure gauge, it varies with rpms/poppet I assume? So what should my idle/mid/wide-open be for good pressure and when should I be "concerned" as far as low readings?
 
I can give you some (general) Merc numbers but I assume it varies a little from model to model.

Yes, the water pressure varies according to rpms. The poppet spring doesn't even open at lower water pressures so the thermostat controls water flow all by itself at lower rpms.

So, again, in general:

Below 1500 rpms water pressure will be between 1 and 3 psi

The range of the poppet is somewhere between 4 and 9 psi - so at 4 psi it starts to open and above 9 it's pegged wide open (so as much water is the waterpump can send is going basically unrestricted right through the powerhead.

The pressure tends to top out at about 12 psi (which is why the Merc water pressure gauges only go up to 15 while other aftermarket ones are 30 or even 60 psi depending on the application).

Once installed you will get a feel for "what's normal" on your motor - cruise might be 8 or 10 psi, and pushing 12 at WOT. That is helpful because if you notice it's almost never making 8 when you are heavy on the throttle you may have a blockage or it's time to replace the impeller etc...
 
galamb said:
I can give you some (general) Merc numbers but I assume it varies a little from model to model.

Yes, the water pressure varies according to rpms. The poppet spring doesn't even open at lower water pressures so the thermostat controls water flow all by itself at lower rpms.

So, again, in general:

Below 1500 rpms water pressure will be between 1 and 3 psi

The range of the poppet is somewhere between 4 and 9 psi - so at 4 psi it starts to open and above 9 it's pegged wide open (so as much water is the waterpump can send is going basically unrestricted right through the powerhead.

The pressure tends to top out at about 12 psi (which is why the Merc water pressure gauges only go up to 15 while other aftermarket ones are 30 or even 60 psi depending on the application).

Once installed you will get a feel for "what's normal" on your motor - cruise might be 8 or 10 psi, and pushing 12 at WOT. That is helpful because if you notice it's almost never making 8 when you are heavy on the throttle you may have a blockage or it's time to replace the impeller etc...
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Ok I'm not saying your numbers are off, but I am getting different answers on what kit to buy, if you say 12 at WOT and "Merc gauge only goes to 15" that would be the other kit, then faztbullet said get the A04 kit that goes to 30psi. Are these kits the exact same other than the gauge? so 10psi through one kit would still read 10psi on the other kit so it really wouldn't matter what one I got (assuming psi doesn't go over 15)?
 
You are getting hung up on two somewhat unrelated things.

If you are looking to measure the pressure in say a range of 1 to 10 psi whether the gauge is a 0-15, 0-30, or 0-60 it will not effect the pressure that it's reading. BUT it may be harder to tell the difference say between 6 and 10 psi the greater the range on the gauge. On a 0-15 gauge, 10 psi would be two thirds of the way "around the dial", on a 0-30 it would only 1/3 of way etc - think what a speedometer would look like on your car if the max speed on it was 400 mph - when you were doing 50, the needle would not have moved very far from zero (distance wise) - but your speed would still be 50 mph.

Here's the specs from a few different Merc models - as I stated, each has a slightly different pressure range - you just have to decide what meter will work for you. But 10 psi will still be 10 psi even if the gauge is capable of reading 100 psi...
 

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The pressure tends to top out at about 12 psi (which is why the Merc water pressure gauges only go up to 15 while other aftermarket ones are 30 or even 60 psi depending on the application).
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This is TOTALLY WRONG!!!!
ALL Merc 2.0/2.4/2.5 V-6 engines use a 30psi gauge(AO4) and 12psi in the minimum pressure you want to see at WOT. Most will be in the 18-22psi range at WOT but yours may be higher as you have the o-ring heads. A 15psi gauge will stay pegged on a V-6 unless at idle. Also the reason the aftermarkets gauges are indexed/read higher(60psi) is that the newer engines especially the Etec GenII engines run 30-40 psi thru block and that's why most have went to digital sensor/gauges
 
What's typical of the older (pre-1980s) Mercs?
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2.0/2.4 early motors idle is 3-7psi and WOT 18-22psi...2.5 motor motors 1-4 psi idle and 12-20psi WOT due to way poppet design. That also why it takes so long to "P" as t-stats must open on a 2.5......
All inline motors with no t-stat/poppet are 1-2 psi at idle and 5-10psi at WOT depending on build up in exhaust plate.The cleaner the plate and crossover holes the higher the psi. Also mounting location on Iline as if use port between sparkplugs it will be lower than coming off top of block above exhaust divider.
 
faztbullet said:
That's the coil mounting plate bolt marked with arrow.....That hose if it comes off the bottom adapter plate on a warer fitting that's your pressure hose which it should be. Use the Merckit 79-895288A04 as it 30psi and the A01 is 15 psi for inline motors.
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So my part (79-895288A04) came in... Its just the gauge. Is there a kit part number I was supposed to get? At the least I can think of I still need tubing and an adapter to put the tubing onto the gauge.. Do people sell just those parts? Or should I return this for a "kit" (if there is such thing do you have a part number)?
 
You need to buy the kit, I did the same thing brought the gauge and not the kit. You can find the part number google mercury water temp kit it is easy to install.
 
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