Looking for some help here, 502 Mag EFI Bravo 1, low water pick up in a 27 Fountain. Engine was overheating, changed out the impeller and housing....it was toast. We back flushed the engine and removed all impeler peices. Boat runs like a champ on the hose (factory flush system on the boat) has good water pressure and runs 140 water temp. Put it in the water and it overheats and has no water pressure. I'm not getting water from the drive. Any thoughts?

The hose fitting in the gimble bell housing may be corroded.

Your factory flush system might not be sealing. My boat had a problem like this and the hose hook up was not sealing.

Lets take this in steps. First: Is the o-ring that seals the drive to the helmet in place?
Check the water hose that is molded from the helmet to the transom, in good shape, at that time inspect the plastis sleve that inserts into the hose not crushed, if thats good. Remove the 1 1/4 intake hose from inside the boat, then remove the plastic adapter. 2 1/4 bolts ( this will take some time, small 7/16 wrenches will help) look for the plastic sleve insert. Is it crushed? This seems to be a common problem on the hose and sleves becoming cushed from corrosion in these areas.
Hope this helps.

Thanks. I'll let you all know what I find.

If you have the Fountain factory flush, are you sure you have the two valves set right? The 1/4 turn valve should be in the closed position for sure, and the gate valve open (If I remember correctly). If the gate valve is in the wrong position, you will get no water from the outdrive to the engine. As a check, open the 1/4 turn valve with garden hose attached and water flowing through it, with the engine off. Check to see if you get water flowing back through the outdrive and running out the outdrive's water pickups. If the gate valve is set right, for normal boat operation, you should see water backflowing through the outdrive. If it is set wrong (for normal boating) nothing will backflow out the outdrive. If you block the outdrive water pickups, you can effectively, within reason, pressure check your water intake hoses, too. I have never seen the 1/4 turn ball valve or the gate valve have sealing issues on any of the Fountains that I or any of my friends have owned.not saying that that is not possible, but unlikely. Check the simple stuff first.

Good point. I remember this on a 38 with twin and you always had to be certain all gate valve were in the correct position depending if your running on the hose or in the water. Almost sounds like this type of a problem. Possible bad valve??

Pull the plastic hose fitting off the inner Transom Plate ... 2 bolts ...if its accessable you'll know right away ..... you have not mentioned if there has been any service work done to the drive? If the Hose thru the TA was replaced it can spin and twist when you tighten the threaded insert and cause low water pressure and overheating .......m

THanks Bob, I checked that and found that with the hose on and engine not running, water runs out of the water pick up on the drive with the gate valve (round handle) in both the open and closed position. I took the hose off right at the valve, and water comes out of the valve no matter if open or closed, so water is flowing TO the drive from the flush system. WHen you start the engine, the water flows through the gimble and the exhaust.

Bad valve? Corrosion in the gimble? I'm stumped.

Also, have not had any recent drive work or service done (other than oil)

The plastic sleeve insert going through the transom is collapsed/crushed. I'm no mechanic, so it's going to Total Marine Performance...Have them give the entire housing assembly a once over.