Volvo 5.0 GXI-E overheating at high rpm cools at low

[2mcneil]

My 2004 Caravelle 218 Deck Boat with a Volvo Penta 5.0 GXI-E is overheating at high RPMs but will cool at low RPMs. I've replaced the impeller and that didn't fix it. Since it was the holiday weekend and I couldn't get any other parts, I took out the rusty thermostat and left it out and tried again. Out of the water on a hose, it didn't overheat. Put it back in the water and it did. I've checked the temperature with a heat gun tester and nothing seems hotter than about 170. On the water, the gauge shows about 205. What should I look for next? I've removed one of heat risers and it looks good, I haven't taken off the other yet. I have no experience with boat engines, but lots with automotive engines. Any help would be greatly appreciated. Thanks!

 

[PatinIdaho]

Sounds like a partial plug someplace. Could not tell ya where to look but im sure some one will.
Staying cool in the driveway is because there is no load on the engine. At the lake it's under load and working hard!

 

[dypcdiver]

First place to test is the thermostat housing the 2 outlets that go to the fwd ends of the manifolds can rust up at the housing and also at the manifold end. That would restrict the out flow of cooling water.
You could also disconnect at the manifold the hoses and just for a few seconds run the motor with the hoses in a bucket to check for flow.
Also make sure the outdrive leg inlet holes are clear of weed or debris.

 

[2mcneil]

Thanks

 

[Tail_Gunner]

This is more common than one might think, the boat is ten yrs old its seem some use. The impeller you changed is made of rubber and they will fall apart over time,,,the vanes literally rip off and get pushed into the cooling system lodging in and blocking water flow. So you need to back flush the engine hoping to dislodge them under the highest possible pressure you can generate, open the brass plugs in the back of the manifold and flush well...turn your thermo stat housing upside down and inspect all the possible passages and yes they lodge up in there.On the back of the engine there is a power steering cooler that is another bottle neck.

It is a pain and take's some time to do but more than probably you will find a few vanes lodged in the system...and one of the reason at the end of each year it is a good ideal to change that $40.00 part..just saying...

 

[kccoe]

My Volvo penta gxi did exact same thing. Mine was the raw water inlet hose nipple. The nipple is black plastic and it was crack . This cause the impeller pump to suck air instead of sea water when the boat was on plane because this nipple is above the water on plane. You can do the bubble test by getting a clear piece of plastic hose . Connect it to the inlet side of the impeller pump and get a hose nipple and connect it to the raw water inlet hose. You must test while at sea or get a large plastic tote that is taller than your water inlets on outdrive . Place tote under outdrive fill with water and leave hose running in the tote. Water level must be above inlets. Ear muffs have to much pressure and will hide bubbles if an air leak present .Crank engine if you see bubbles and air in clear hose you have an air leak in your outdrive raw water system . It will not cool the engine . Feel the nipple connection for the raw water hose to the lower unit too see if broken or could be the seal located around the raw water pickup tube in the lower unit