Very high water pressure
 

Hi,
I have a problem with my 2000 502 MPI. I had a broken impeller (one blade was already missing) so i put in a new set, impeller, wear plate and housing. First test drive i saw more than 35psi water pressure (35 is max on my gaffrig) and the big water hose from t stat housing to waterpump has been so big that the serpentine belt cut it. I looked everywhere to find the missing impeller blade, but couldn't find it. The water pressure is taken where you can drain the block near the starter. So the blade couldnt be before the oilcooler. And when it went trough the oilcooler it should be so little pieces that they are already out. Courius is, when the boat is in no gear (0mls/h) and 5000 1/min there is 25psi water pressure, when it drives 50 mls or more there is more than 35psi. Could there be a problem with the new raw water pump? Any other ideas?
Thanks from Germany / sorry for my bad english
Andre

The missing piece is blocking the water flow somewhere. Have you checked for blockages in the hoses going to the exhaust. The missing pieces usually get caught in the oil cooler since it is the first thing downstream of the raw water pump. Because The water hose after the oil cooler is expanding then it has to be on the exit side of the engine water circuit.

x2

I checked the t stat housing, the hoses to the exhaust and the exhaust. Nothing in and a very free flow. I think the pieces couldnt be as big to block anything when they went trough the oilcooler.

Disconnect the hose that runs from the Raw pump to the oil cooler, at the Raw pump end... remove the water hose inlet at the T-Stat housing (on the right side when looking at the engine. Flow water from a garden hose through it and this will backflush the oil cooler.... the pieces could very well be stuck inside the cooler.

Did you put the tstat spacer back in orientated correctly + with the tstat on top ?

Did you know with the tstat closed, it closes off just one way the water goes to the top of the tstat housing where the exhaust gets its water ?

Yes, there are two levels to the tstat housing.

http://www.mercruiserparts.com/images/COMMON/36327.png

The blockage has to be in the engine or the exhaust - If it was before the engine than the hose connected to the engine would not have swelled. Every few years I pull the ends off of my oil cooler and push a brass rounded end brazing rod through each tube. You would be surprised at how much junk you will get out and how many tubes are blocked.

Lets ask is this a saltwater boat, if so how bad or not is internal corrosion , & scale built up in the t stat housing and necks and in the exhaust manifolds & risers water jackets ? How old is the water circ pump ? Is all of this stock OEM set up and equipment ?

Not knowing - you did not mentioned that this was a closed cooled app ? so is it or not ?

Is the impeller and housing a stock OEM set up and a stock OEM replacement that you installed ? Is your water pick ups stock in the outdrive or do have any other means for water intakes or water inlets ?

Just asking because 8 out of 10 times up here nothing is stock so very hard to figure anything out including a fix. I have learned the hard way and now will ask all indepth questions about what the set up is and what is OEM or not designed and installed.

Its a saltwater boat, low water pickup in the drive, always flushed and kept on a lift, older water circulation pump, 10 years old stainless marine exhaust, replacement raw water pump i think, no closed cooling.
The high pressure happens only when i drive more than 50mls. And the fault is from one day to the other. I only changed the raw water pump because there was no water flow.

...deleted my previous response....

On second thought, your restriction is likely after these coolers - I just re-read about your water pressure pickup. Sound like thermostat housing and beyond is where you need to look (restriction in thermo housing or exhaust).

I had this one time, but this caused low water pressure.
http://i16.photobucket.com/albums/b1...7/5e0a906c.jpg

Does not have to be impeller fragments that are causing the blockage.

.....but it´s till i had no water flow out of the exhaust. I changed the impeller set and the pressure was as high, that my hose was cut imediately. Perhaps the hose was old and couldnt handle high pressure, but the water press gauge showed curious data too.
I wanted to test my water press gauge, now its broken :picard1:

IMO you need a new hose and possible a new water circ pump and double check for restrictions like I asked in the t stat / housing and necks and the exhaust / manifolds and risers - water jackets. just my 2 C s

i have a new hose, but i wont destroy it. I think the circ pump cannot be the problem. When the t stat is closed the engine doesn´t pick up new water. The pump will only pump around and when i´m not in drive (0mls/h) and 5000 rpm there is no problem.
All goes through a small bypass direct to the exhaust when it´s cold.
I ordered a new raw water pump and will make a test drive at the weekend. I´ll reflush it once more and see what will happen.
I´´ll keep you informed.
Thanks so long for helping

I cannot see the pieces getting thru the coolers as the holes are not big...back flush each, but you may have another issue

Since psi guage is in block, only thing after it (block) is heads, intake, t-stat housing, exhaust.

That's where the problem is going to lye.

Are you sure head and intake is possible? When the t stat is closed the engine doesnt pick up new water. It´s only going round (water pump - block). IMO it could only be blocked in the t stat housing or exhaust. I cleaned the t stat housing and sand blasted it as good as i came in. I´ll reflush the exhaust and see what happens. Unfortunately i´ve broken the water press gauge. So i will have to improve.

When your motor is working correctly:

When the tstat is closed some water goes back into engine and much goes into exhaust.

It's a beautiful design, that Merc t-stat housing is.

It recirculates water back to the motor to warm it up quicker and to keep engine water temps more consistent, yet flows water to the exhaust full time.

What he said. The raw water pump is always pumping, otherwise the exhaust would melt down immediately.

Had a couple stuck thermostats cause enough pressure it burst the hose from the circulator pump to the tstat housing

Are you sure? I checked the t stat with a small mirror. At the entrance of fresh water the t stat divides in 2 ways - 1) engine and 2) exhaust & upside the t stat. There is no possibility for cold water in the engine getting out to the exhaust. All fresh water have to go through the bypass to the exhaust - and its a small bypass....

For visualization in trouble shooting try 4 ea. Pieces of clear reinforced hose about 4" to 6" in length (from h/w store).
Put one side to t-stat lines and barb connect other end to factory hoses.
Now you can see how the water, is/is not, flowing.
"a moving picture is priceless"

I'm positive. Exactly as I described. I dissected one (cut apart) because I was having a water psi issue on the dyno with a motor I had set up full wet.

Sounds brash........do not doubt me on this one. LOL.

Sb,i know you are right, just giving op a way to see for themself how it works and see where water is/not flowing.
All of your expert advice is much apericiated by me and many others to be sure.
Thanks again.

I totally agree with the clear hose water hoses and this how we check a lot of cooling related problems - next is to buy different thin walled as well as thick wall clear hoses, The thin wall hoses placed in areas will expand showing possible too much water pressure if needing to check. and off course the thick wall clear hoses should be used on any part that has the suction side of cooling so hose does not collapse. Anyways just throwing it out there.

Could his thermostat/diverter spacer be in wrong?

Yes, especially if tstat is mounted under spacer instead of on top. That spacer provides warm and cold water direction. The t-stat provides hot water direction.

Also, the relatively small holes connecting the lower chamber to the top chamber (the exhaust water comes from the top chamber) are plugged (easy to happen because of size) this will cause water not to come out of exhaust until the t-stat opens.

So....chances are at this time, those smaller holes connecting lower chamber to upper, are plugged.

^^^^ Agree with this ^^^^ this exactly what I was talking about look for restrictions - T-stat and or the T- stat housing and or necks in post # 13.

YOU just explained it a whole lot better and in more details than I did

Okay, found pic of cold/hot water flow thru the Merc t-stat housing that I made years ago.

See post#9 here: http://forums.boatfreaks.org/showthr...t-stat+housing

I go on to describe it a little further.

I made a test drive yesterday. Now i read 17 PSI at 5000rpm and 0mls, 30PSI at 50mls and 35PSI at 70mls. No hose burst, but it´s a lot pressure. A friend has 22PSI at 65mls (WOT) with low water and the side pickup. I only have the lowwater pickup.