Volvo Penta overheating issues

[Kearn4344]

I have a 2003 volvo penta 5.0L GXI with SX-M 1.60 sterndrive. I have replaced thermostat, manifolds and risers, the hose from the transom through the gimbal housing connecting to the sterndrive along with nipple that goes through the gimbal housing, o-ring to the nipple, and the o-ring that sits between the gimbal housing and the sterndrive itself. I have noticed that after I get on plane the temperature creeps up to almost the high temp alarm. When I go back to idle speed the temperature goes back down. This is a repeating process. What could be the problem here. Am I sucking in air somehow and where would it be coming from since this only occurs on plane. Thanks

 

[alldodge]

Might be sucking air or other
Have you verified it is over heating with an IR temp gun measuring the thermostat housing?

Get a piece of clear hose and a barbed hose fitting at the hardware store. Place the short piece between thermostat housing and hose from the raw water pump.

 

[Lou C]

There was a member on here or one of the other forums that had a similar problem. What they found was that a hole had rotted in the water transfer tube that is inside the drive. It can also be the rubber grommets for this tube

 

[dypcdiver]

I agreed that it could be either of the 2 rubber seals at each end of the tube.
That was me who had the hole burnt through Lou C.
However my symptoms were overheating at idle, anything over 1500rpm was cooling normally.
I put a pressure test from the plastic nipple to the T'stat and it held 10psi for 30mins, so decided that the raw water pump was past its best, that was an expensive misdiagnose.

 

[BRICH1260]

How`s the impeller look? Replaced it lately?

 

[Lou C]

I agreed that it could be either of the 2 rubber seals at each end of the tube.
That was me who had the hole burnt through Lou C.
However my symptoms were overheating at idle, anything over 1500rpm was cooling normally.
I put a pressure test from the plastic nipple to the T'stat and it held 10psi for 30mins, so decided that the raw water pump was past its best, that was an expensive misdiagnose.

Yes now I remember. Getting the drive apart can be a trial if used in salt water, I used some bolts and 3 scissor jacks to get mine apart.....take a close look at this pic, I put one jack under the 2 bolts on the front mounts and one under each side of the long one that goes through the trim ram rod hole. This puts the force on the strongest part of the drive so you don't break anything.

 

[Kearn4344]

Might be sucking air or other
Have you verified it is over heating with an IR temp gun measuring the thermostat housing?

Get a piece of clear hose and a barbed hose fitting at the hardware store. Place the short piece between thermostat housing and hose from the raw water pump.

Thank you for you response, I have check thermostat housing and everything else around with a IR temp gun. It seems on par with the gauge on the dash. I have not tried the clear tube method yet but I will. Am I looking for bubbles?

 

[Kearn4344]

There was a member on here or one of the other forums that had a similar problem. What they found was that a hole had rotted in the water transfer tube that is inside the drive. It can also be the rubber grommets for this tube

I have not thought of that but I will take it apart and inspect, probably will just go ahead and replace them if I can since the lower unit will be separated from the stern anyways. Thank you

 

[Kearn4344]

How`s the impeller look? Replaced it lately?

The impeller is new. I replaced it a few months ago. The old impeller still looked new but I replaced it anyways.

 

[Lou C]

Thank you for you response, I have check thermostat housing and everything else around with a IR temp gun. It seems on par with the gauge on the dash. I have not tried the clear tube method yet but I will. Am I looking for bubbles?

yes that will show that you are sucking air in from somewhere, could be the water tube/gaskets in the drive, pivot housing plastic fitting or even the impeller housing.
The other thing that can cause overheating is leaking cylinder head gaskets which requires a major repair, what happens is that combustion gas gets into the cooling water. This will be evident if you replace the hoses that go from the 'stat housing to the exhaust manifolds with clear hoses. If when the engine warms up (stat open) with the boat in the water you see bubbles in these hoses its likely the head gaskets are leaking.

 

[SD2600]

I had the exact same problem a few years ago after i installed a new engine. I chased it in circles for some time. My solution which may not be perfect for everyone one has worked ever since.

I can't find the exact diagram but hopefully my description may lead you to a solution.
if you follow part number 29 in the diagram to the opposite side of the drive. there is a plastic fitting it is square with a round section your pickup hose connects to. there is a small hole in the bottom of the square portion that allows water to drain out.

This fitting in my application would not seat perfectly in the drive do to some corrosion to the housing. I tired triple guard grease to help seal it in its spot. this worked for a few hrs on the water but eventually the grease would break the seal causing air to enter the system and trigger the overheat.

my solution was marine-tex. I mixed up and set the plastic fitting in its home while on the ramp. i let it cure a few hours and just like that my overheat issue was fixed.... hope this helps keep us posted

 

[QBhoy]

What temperature is it actually getting to ?