I have a strange problem on my 2003 6.2MPI Horizon (Closed cooling) Mercruiser, Bravo II sterndrive. The engine Guardian modes at around 4200rpm, constant alarm, forced throttle down. Normal operation resumed once idle is reached. (If you wish to skip the detail, the question that can be posed without the history is really "While I might not get full pressure, I should expect more than 2psi sea water pressure on the flushing ears, surely?". For "what else could be the cause" needs a bit of a read Im afraid!)
I have made some progress, as follows:
On the water the scan tool shows a raw water/Block Pressure of no greater than 3-5 psi (it seems to vary) at any revs below 4000. So this would certainly cause Guardian mode. I also notice at sustained high speed (under 4000 of course) the temperature on the gauge and the scan tool gradually increases by up to 5F over the span of say 5 or 10 minutes. It doesnt seem to go beyond this though.
Both of these facts lead me to believe there is insufficient water being picked up by the raw water pump. So here's what I did:
First, for good measure, I replaced the raw water pressure sensor with the more recent/modified part. The moderate temperature rise suggests this isnt the cause, and that there is in fact really low pressure - and so I wasnt surprised at ......
No change to symptoms.
Second I pulled the (brass) water pump. Impellor looked fine, top and bottom plates had some scouring, sides looked fine. So I put a repair kit (stainless top and bottom plates, new impellor) through it.
No Change to symptoms.
Third I replaced the through the transom water pickup hose with a modified kit from amarket.com. The existing hose did have two quite reasonable indentations at the point of entry through the transom due to corrosion, which would most certainly have restricted flow to a degree (id estimate around 50%). This is a known problem on the Bravo II drives.
No change to symptoms on the ears at least.
Yet following this last fix, on the flushing ears raw water pressure is still reading only 1-2psi even at 2000rpm. I believe this means it isnt fixed, although Ill have to put the boat back into the water to be sure - however I find it hard to believe it cannot generate more pressure than 2psi on the flushing ears, esecially given Im looking for at the very least double digits.
There do not appear to be any air leaks in the hose from the transom to the pump - its a pretty short fat hose anyway.
So Im now a bit stumped, assuming that is I've eliminated any restriction before the pump and the test on the ears is valid.
Low raw water pressure CANNOT be from any blockage after the raw water pump, as that would cause high pressure, not low. So if not an intake restriction or the pump, then it could be from lack of restrictions after the pump, but that would have to be the heat exchanger - and I would have thought it has to be really shot to let that much water through that the pump cant hold pressure. And Id expect to see some serious overheating.
I have clearly made an incorrect assumption to conclude nothing is wrong, because it clearly is! Anyone got any ideas - Im just about out of them, but Im not giving up!!!
I have made some progress, as follows:
On the water the scan tool shows a raw water/Block Pressure of no greater than 3-5 psi (it seems to vary) at any revs below 4000. So this would certainly cause Guardian mode. I also notice at sustained high speed (under 4000 of course) the temperature on the gauge and the scan tool gradually increases by up to 5F over the span of say 5 or 10 minutes. It doesnt seem to go beyond this though.
Both of these facts lead me to believe there is insufficient water being picked up by the raw water pump. So here's what I did:
First, for good measure, I replaced the raw water pressure sensor with the more recent/modified part. The moderate temperature rise suggests this isnt the cause, and that there is in fact really low pressure - and so I wasnt surprised at ......
No change to symptoms.
Second I pulled the (brass) water pump. Impellor looked fine, top and bottom plates had some scouring, sides looked fine. So I put a repair kit (stainless top and bottom plates, new impellor) through it.
No Change to symptoms.
Third I replaced the through the transom water pickup hose with a modified kit from amarket.com. The existing hose did have two quite reasonable indentations at the point of entry through the transom due to corrosion, which would most certainly have restricted flow to a degree (id estimate around 50%). This is a known problem on the Bravo II drives.
No change to symptoms on the ears at least.
Yet following this last fix, on the flushing ears raw water pressure is still reading only 1-2psi even at 2000rpm. I believe this means it isnt fixed, although Ill have to put the boat back into the water to be sure - however I find it hard to believe it cannot generate more pressure than 2psi on the flushing ears, esecially given Im looking for at the very least double digits.
There do not appear to be any air leaks in the hose from the transom to the pump - its a pretty short fat hose anyway.
So Im now a bit stumped, assuming that is I've eliminated any restriction before the pump and the test on the ears is valid.
Low raw water pressure CANNOT be from any blockage after the raw water pump, as that would cause high pressure, not low. So if not an intake restriction or the pump, then it could be from lack of restrictions after the pump, but that would have to be the heat exchanger - and I would have thought it has to be really shot to let that much water through that the pump cant hold pressure. And Id expect to see some serious overheating.
I have clearly made an incorrect assumption to conclude nothing is wrong, because it clearly is! Anyone got any ideas - Im just about out of them, but Im not giving up!!!
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