Temp gauges not reading

"Hello all im new on forum and

"Hello all im new on forum and need some advice. I have a 95 merc 5.0LX alpha 1. Last spring (07) i had overheating issues and replaced the impeller in foot. Solved the problem. Next time out after long day on water my warning buzzer went off and i had low oil psi, about 5psi. There was a slight knocking in motor. Next day messed with it out of water with ears and nothing. I thought it might be bearing in motor so drained oil again and put 20/50 with a bottle of lucas. Ran it all summer with good oil psi, about 20psi after hot. The only time it knocks is when its hot and on water at idle, 1000rpms goes away. Now different problem, i just took it out 1st time since last year and my temp gauges aren't reading when engine is running. Ran it for 20 mins at 3500rpms and gauges never moved. I shut it down and my mech gauge i had put in last year went up 160. Turned the key with out staring, my elect gauge reads the same. Fire it up , they both go down to 100 or less. Motor was normally hot. I took out termostat it was open then i let it cool down and it shut. Ran it for another 20 mins gauges never moved. I felt the termo housing getting hot then cool, so that seems to be working. Anyone got a clue? Thanks again."

"My thoughts: The temp sender

"My thoughts: The temp senders won't read if there is trapped air, steam or water vapor in the cavity. If the engine is FWCooled then you need to bleed out the air. If RWC then perhaps the OD impeller is worn again and not pushing enough water.

"Ran it all summer with good oil psi, about 20psi after hot."

That is on the low end of the oil pressure range. Try straight 40 wt. oil."

"Thanks guy i will pull down l

"Thanks guy i will pull down lower unit this weekend and check out the impeller. Now on the oil psi i was thinking, do you think my oil cooler could be bad? Like i said, my oil is very hot and that might be why the motor knocks when hot. The oil is thinning out to much maybe. If so is there a way to check the oil cooler? I really dont think its a bearing cause i wouldn't have any pressure at all."

Steve:

The oil cooler may b

Steve:

The oil cooler may be partially plugged internally and externally w/debris from a former impeller and unable to dissipate sufficient heat to the cooling water which could also be why there is not enough water in the engine to give temp readings.

Pull it out and clean it both the oil line and the water jacket. Replace if need be.

Thanks guy i'll get on it

Thanks guy i'll get on it this weekend and let u know how i mad out. You've been alot of help.