Water Pressure Question

[JGra]

I have been putting and old boat back together since about the middle of the last summer. I have most of it done and took it out for a sea trial right before it started to get cold. I really did not winterise it other than adding some sea foam as I planned on using it over the winter. After all its not normally this cold in the south. Anyway I cranked up the motor today (try to do it at least once every 2 weeks) to run it for awhile. Motor cranked right up and ran real good. Had a good stream of water out of the tell tale. After doing alot of reading on this board about the importance of having a water pressure gauge. I had bought a water pressure gauge about a month ago and since it was a decent day I decided to install it. It was a simple job to do. I just tee'd into the tell tale and ran the line up to the gauge. My question is the pressure. I only seem to be getting 2-3 psi sitting there at idle. Now granted I am running on the muffs. Once I bring the idle up (not too high) I can get it up to about 4 psi running at no more than 1500 rpms (again I am on the muffs). I know from what I have read this is kinda low but it seems to have a great stream. I double checked the line for kinks and all is good. Am I not getting a good reading because of running on the muffs. This is a new to me 89 90 3 cyl mercury that I had bought middle of the summer. I was told water pump was replaced first part of the summer (so thay say). Should I put it in the water and run it first before installing a new water pump. Could use some advise. Thanks

 

[crappiejig]

Re: Water Pressure Question

Ideally you should put a 90 degree fitting on your rear cylinder block cover.You will see a pipe thread plug near your #1 cylinder.As far as your psi readings,being hooked up to muffs will throw off your numbers,as you are introducing water pressure via the hose.My service manual on my 60hp merc,also a 1989,calls for a psi of 2-5 psi at 2500rpm.I am certain your water psi should be greater than my 60 with a small impeller.

 

[Texasmark]

Re: Water Pressure Question

Your pee stream is bleading off your pressure. You have to use relative readings as a result and your reading will be much less that you would have with a closed system. So if you read at least 1/3 of 6psi at idle and 1/3 of 10-15 psi at WOT (bigger engine numbers, looks like crappyjig nailed the numbers for the smaller engines) but still 1/3 of those numbers, you should be good to go.

Mark

 

[sschefer]

Re: Water Pressure Question

The tell-tale is not the correct place to get true water pressure. You need to take it at the cylinder cover like was said before. There is a plug there for this purpose. Remove the plug near to #1 plug and use one of the suitable fittings that came with your kit. Your engine requires a high volume water pump. You should read around 6-8 lbs of pressure.

 

[JGra]

Re: Water Pressure Question

The tell-tale is not the correct place to get true water pressure. You need to take it at the cylinder cover like was said before. There is a plug there for this purpose. Remove the plug near to #1 plug and use one of the suitable fittings that came with your kit. Your engine requires a high volume water pump. You should read around 6-8 lbs of pressure.

Thanks for all the great advise. I kinda thought I was loosing pressure through the tee. I see the plug everyone is talking about and even took it out but was not sure I had the right one. I think I will put the tel tale back together and get a fitting for the other port. Even when I took the hose off the back of the gauge while the motor was running the water coming out was nothing compared to the tel tale. I will give it a try and report back. Thanks again everyone.

 

[JGra]

Re: Water Pressure Question

Thanks for all the great advise. I kinda thought I was loosing pressure through the tee. I see the plug everyone is talking about and even took it out but was not sure I had the right one. I think I will put the tel tale back together and get a fitting for the other port. Even when I took the hose off the back of the gauge while the motor was running the water coming out was nothing compared to the tel tale. I will give it a try and report back. Thanks again everyone.

Installed the the fitting on the block and ran the hose to that. Got aout 1 psi better. I think I am going to try it in the water instead of on the hose and see if its gets any better. I might even trhow a water pump in it just for my piece if mind. Stream seems good to me but maybe it should be better. Kinda new to these bigger outboards.

 

[Silvertip]

Re: Water Pressure Question

I have a 75 Merc with a WP gauge "Tee'd" into the tell tale and I am not surprised that when the poster switched to the engine block it didn't change much. Mine reads about 7 psi at idle and 14 at cruise with a new pump. Connecting to the water jacket may be necessary on some engines but not on this particular engine. The tell tale amounts to no more than a pinhole leak in what is otherwise a wide open cooling sytem. Remember, cooling water goes out the engine through the exhaust as well as the mist that exits the idle ports at the back of the engine so much more pressure is lost through those ports than the tell tale. The idea of a water pressure gauge is to also install a new impeller. You then know what "normal WP" is for that particular engine provided the rest of the system is working properly (thermostat and bypass valve). Any deviation down the road from the observed idle and wide open throttle readings indicates the water pump needs attention. What may appear to be a strong stream may not in actually be appropriate water pressure.

Here is a picture of my setup.

 

[sschefer]

Re: Water Pressure Question

Silvertip, that setup would work too. Most try to just run the tee straight through with the wp gauge comming off the side. That's the way it's shown in the Teleflex install guide that I got too. Comming straight off the cylinder cover is my preference since its as direct as your gonna get without any additional loss. Your setup works good too but ya gotta think about what your doing. My method keeps me from having to think

 

[Silvertip]

Re: Water Pressure Question

It doesn't matter where on the T the hose comes off. Mine worked just fine with the T off the 90 degree side. I had to change it because the T hit the cover. Pressure is pressure. It doesn't care whether there is a 90 degree bend in the line. Besides, the port you mention is a good place to put the water temperature sender for the tempt gauge which the engine should have in addition to the water pressure gauge.