5.7 Volvo Penta Overheating at Idle

[baker7007]

My 5.7 VP overheats at an idle only after a run (never from cold start up). I can run up and down the lake all day at 170 but when I bring her to an idle/in no wake it goes up to 220 but no alarm or limp mode. Get going again at 3k+ rpm and I can watch it come down. Shop changed impeller, t stat, and rubber grommets in lower drive (3 different shops visits) but still overheats. I know it’s not the gauge because oil pressure at idle also drops which validates heat. Checked risers and they are clean. Any ideas?

 

[alldodge]

I know it’s not the gauge because oil pressure at idle also drops which validates heat

From cold to warm it would do that also
Use a IR temp gun and measure temps at thermostat housing and elbows. If the thermostat housing (temp sender location) was at 220* rubber hoses would be smoking

 

[kenny nunez]

What year and model drive do you have? how long has this been happening? When the temperature goes to 220 on the gauge does it ever go back down if you just let it idle?
Do like AD said about using a IR temperature sensor.

 

[baker7007]

@alldodge are you thinking it’s not that hot? When I said oil pressure dropped I meant further than normal at idle when hot - around 10 lbs.

@kenny nunez it’s an 05. I believe it’s a VP sx. It’s been happening since the shop did offseason maintenance: new impeller, motor and drive oil and filters - first time I took it out it did it. No will not drop if I just let it idle - have to get moving or shut off to wait a bit.

 

[alldodge]

With info provided I was thinking maybe it wasn't over heating. Did say anything about other checks other then the boat gauge

 

[baker7007]

@alldodge the risers are super hot to the touch as well as oil filter housing. I took it back to the shop that did the impeller and told them what it was doing. They said they check the impeller and then they went to thermostat. When that didn’t work I took it back and that’s when they said it was the rubber grommet in the lower drive unit. Finally this weekend I had enough and I just pulled at home. I pulled the impeller myself and it looks fine.

 

[alldodge]

OK, its getting hot
Look on top the drive where the water hose connects coming from the drive. Remove hose and the fitting. @Scott Danforth has found the fitting gets corroded up and needs to be replaced

 

[baker7007]

@alldodge is the hose/fitting on the back side by the drive or inside engine compartment?

 

[kenny nunez]

Inside the thermostat housing there should be a small bypass port that that lets water circulate when the thermostat is closed. I have seen them to be either partially or completely plugged with corrosion causing a similar condition.

 

[Lou C]

Ok it is important to know which Volvo system the OP has, there are the Swedish drives (AQ and its variants) and the SX drives (partly based on the OMC Cobra). I'm not familiar with the AQs but on the Cobras and Volvo SX there are a few common points:
1)Plastic water nipple in the transom mount, if this cracks because of trapped water it will suck air when the boat is on plane
2)Rubber water tube grommets in the drive, if you have one bad overheat or even chronic low level overheats they can get overheated by exhaust gas and not seal well, can suck air with the boat on plane
3)What Kenny mentioned above, the bypass in the thermostat housing, can get clogged, this actually happened to me once. Rodded it out with the boat on the mooring.
The OMC and Volvo thermostat housing is actually the same part, or at least it used to be. I replace them after about 8 years use in salt water same with exhaust elbows. They just get too corroded to not have clogging issues.
On the plastic water nipple in the transom mount, the OMC Cobra system had a drain plug there, that you should remove when winterizing it that allows water to drain so it does not crack. Not sure of all years of the SX had the same water drain.
Other possible causes:
Due to the engine mounted impeller, any air leaks into the cooling water flow will cause problems. You might try getting some reinforced clear hose, replace the impeller to stat housing hose with this, see if there are bubbles in the cooling water, if so air is getting sucked in somewhere between the drive and the impeller housing.
You can also check for blown head gaskets that are allowing combustion gas into the cooling water, by doing the same thing with the feed hoses from the stat housing to each exhaust manifold. If you see air in the water flow in those 2 hoses, but did not see it when testing the impeller hose, then that's a sign the head gaskets could be starting to leak, which can definitely cause overheating....this won't show on a cold engine but when the engine warms up enough to open the thermostat housing it will....

 

[baker7007]

@Lou C thank you for the detailed info.
1) will check nipple in transom mount (I assume it’s accessible without removing drive?).
2) rubber grommets were replaced in lower drive unit (attached to copper tube)
3) will check for blockage in t stat housing
4) will check for air leak
5) shop did compression check to rule out blown head gasket + no water in oil.

Question: do the impeller housings ever go bad? I can tell it’s original (2005) because 1) it’s red/same color as motor and 2) it’s the metal/plastic version (not all brass).

Problem seems to be a low flow/pressure issue...what are signs of bad water circulation pump?

Than

 

[Lou C]

The water circulation pumps (just a marine version of a standard Chevrolet small block water pump) rarely go bad and when they do the bearing makes noise and you can get a leak from the weep hole located at the underside of the pump. The are pretty cheap and easy to replace.
I would first probably want to do the clear hose test on the hose from the impeller housing to the stat housing, do it with the boat in the water and see if you get air in that water flow. Now there is a "Volvo Penta Overheat Diagnosis" PDF document floating around the net that you might be able to find and print out. Get a hold of it and do all the tests suggested and you will likely find the problem. I do think their impeller housings can leak air, if they leak water which has been reported before.
The plastic nipple, you can test it as follows:
put duct tape on the water intakes of the outdrive to seal it up.
tilt the drive up a bit so you can see the hose that goes from the drive to the transom mount
disconnect the hose from the transom mount to the impeller housing
Have an assistant fill that hose with water while you watch for drips from the joint between the drive and the transom mount, if you see water leaking it could be the nipple or the short hose. To do either the drive and pivot housing need to come off.
Since I always drained mine and filled the hoses with antifreeze I have never had to replace that plastic fitting. 33 years old and counting.

 

[BRICH1260]

In addition, make sure you do not have more than one O ring on the Impeller pump housing. Sometimes they get one or more stacked and cause the pump to suck air. Happened to me.

 

[baker7007]

The water circulation pumps (just a marine version of a standard Chevrolet small block water pump) rarely go bad and when they do the bearing makes noise and you can get a leak from the weep hole located at the underside of the pump. The are pretty cheap and easy to replace.
I would first probably want to do the clear hose test on the hose from the impeller housing to the stat housing, do it with the boat in the water and see if you get air in that water flow. Now there is a "Volvo Penta Overheat Diagnosis" PDF document floating around the net that you might be able to find and print out. Get a hold of it and do all the tests suggested and you will likely find the problem. I do think their impeller housings can leak air, if they leak water which has been reported before.
The plastic nipple, you can test it as follows:
put duct tape on the water intakes of the outdrive to seal it up.
tilt the drive up a bit so you can see the hose that goes from the drive to the transom mount
disconnect the hose from the transom mount to the impeller housing
Have an assistant fill that hose with water while you watch for drips from the joint between the drive and the transom mount, if you see water leaking it could be the nipple or the short hose. To do either the drive and pivot housing need to come off.
Since I always drained mine and filled the hoses with antifreeze I have never had to replace that plastic fitting. 33 years old and counting.

Thank you - quite a bit to go on here.

 

[baker7007]

In addition, make sure you do not have more than one O ring on the Impeller pump housing. Sometimes they get one or more stacked and cause the pump to suck air. Happened to me.

1 o ring confirmed

 

[baker7007]

What is the circle in middle of impeller housing? Could that cause overheat at idle?

 

[Lou C]

I don’t know what a new one looks like but I’m sure someone here does and can comment.

 

[I_am_Sam]

I'm surprised this hasn't been mentioned yet... Make sure the impeller is installed in the proper direction of rotation. I had this same issue. Pulled the impeller and the rubber "arms" or whatever you want to call them were all over the place. Replaced it and ran it for 2 seasons without ovht issue. pulled the impeller again (routine mtce) and this time the arms looked perfect with them bending in the proper direction. sorry in advance for phrasing, i've been up for 23 hours.

 

[dypcdiver]

When you replaced the rubber grommet in the lower drive did you replace both and inspect the Bronze (copper) tube? As I had this same problem of overheating only at idle.

 

[Lou C]

When you replaced the rubber grommet in the lower drive did you replace both and inspect the Bronze (copper) tube? As I had this same problem of overheating only at idle.

I remembered that but forgot to post it!