Need help diagnosing temperature problem on Volvo Penta 5.0 GL-J

[CapnNemo]

I've got a 2009 Glastron GT205 with Volvo Penta 5.0 GL-J and SX-A drive. I bought it late in the 2020 season and it has less than 250 hours on it. In the past, I've never seen the temperature gauge move very much from 150 degrees, once it was warmed up, at idle or on plane. I took it out for the first time this season, and a quarter mile from the dock, it was approaching 200 degrees. I brought it back to idle, and it slowly dropped to a little over 175. I'd appreciate any guidance on how to diagnose this. Here is what I've done and observed so far:
- ran off the garden hose into the engine water port (no muffs). Temperature went up to ~175 again (idle or fast idle up to ~1200 rpm). This seems to suggest the problem is not due to sucking air at the drive since I bypassed the drive.
- checked raw water impeller, and it looks fine to me (no cracks or tears; fits tight in the housing). I installed it a year ago and I have about 50 hours on it. Owners manual recommends changing at this age. Maybe I should.
- checked engine oil (which was changed in fall when I winterized). Looks fine. No indication of water.
- replaced thermostat with VP 3587597. Still goes up to ~175 on the garden hose. Maybe higher -- I didn't want to push it. So, it doesn't seem to be the thermostat.
- Exhaust manifolds are easy to touch -- seem to be cooling fine.
- top of thermostat housing (above the thermostat, where raw water enters) is cold. Bottom of housing (engine circulation) is uncomfortably warm to touch.

Next, I plan to check the temperature sender (I believe this is VP item 3852029). I can't find any information on how resistance should vary with temperature. Does anyone have a calibration or know where to look? I am kind of doubtful that this is the problem though. Since temperature went much higher under load, this seems like more of a water flow problem, but I'm a novice at this.

Also, my buddy will bring his IR thermometer gun tomorrow to check surface temperatures.

Any suggestions on where to look next? This is really baffling me.

Thanks for your help!

 

[bruceb58]

I would buy an IR temp gun and shoot the temp tight where the temp sender is and verify that your gauge is actually accurate.

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[Senior B]

In your write up you suggest that the problem isn't in the lower leg as it seems fine when running on the hose hooked to the water port and that by passes the drive. That observation makes the drive very suspect. Look at the plastic fitting on the left side of the upper unit that the water hose from the drive to the transom housing connects to and see that it's not cracked. Inspect this with the drive in the up position. Also, run it with muffs on and see if you have good suction and flow and post your results. At 1200 rpm, there should be little to no water flowing past the muff ears.

 

[CapnNemo]

I would buy an IR temp gun and shoot the temp tight where the temp sender is and verify that your gauge is actually accurate.

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Planning to try this today. Hopefully its just a temperature measurement error. But since the temperature dropped ~25 degrees when going from on-plane to idle seems to suggest to me that I am not getting enough water flow through the engine. Maybe its just a red herring. I'll also check the connections at the sender and the gauge.

 

[CapnNemo]

In your write up you suggest that the problem isn't in the lower leg as it seems fine when running on the hose hooked to the water port and that by passes the drive. That observation makes the drive very suspect. Look at the plastic fitting on the left side of the upper unit that the water hose from the drive to the transom housing connects to and see that it's not cracked. Inspect this with the drive in the up position. Also, run it with muffs on and see if you have good suction and flow and post your results. At 1200 rpm, there should be little to no water flowing past the muff ears.

Actually, the temperature is still high when running on the water port (175+ at idle or fast idle). Normally would be 150. So that's why I thought this isn't related to the drive.

 

[Senior B]

Read your post again. I should note to my above that 175 is fairly typical what they run at when fully warmed up. Rated thermostat for Raw Water cooled is 160 but they run at 175. If your exhaust manifolds and Risers are only warm to the touch when running and your at 175, you got no issues. Enjoy your day on the water.

 

[Lou C]

In the drive there are 2 water tube grommets that seal the water transfer tube that sends water up from the lower unit to the upper unit. These can deteriorate over time and cause lowered raw water volume as can that plastic fitting in the pivot housing which can crack. However these factors would cause overheating more so when you’re up on plane where the drive is out of the water partially. The fact that it runs at 175 on the muffs and flush hose on land suggests to me something else. With that same thermostat housing & thermostat my old OMC runs right at 160 on the hose. So I think something else is going on here like the stat is not opening far enough or at the right temp. I usually test them in a pot of water hanging it in the water with a coat hanger wire & an old school auto radiator thermometer. I would check that, and also it is possible you may have clogging in your exhaust elbows if they have never been taken off, checked & rodded out. With a good impeller, thermostat & clean exhaust my old ‘88 4.3 runs at 160 in the water sometimes cooler on plane & the hottest it ever gets is 175 after coming off plane but it soon cools back down to 160. The manifolds & elbows are 90-110 at idle and the hottest they get is 135-140 after coming off plane.
When checking the accuracy of the gauge I have found that the place on the engine that accurately mirrors the gauge reading is the intake manifold right under the stat housing. When the gauge reads 160 the temp there is 145-150.
See if you can find a document called “Volvo Penta Overheat Diagnosis” it is a PDF with all the Volvo specific troubleshooting information you need to track down the cause….

 

[CapnNemo]

Read your post again. I should note to my above that 175 is fairly typical what they run at when fully warmed up. Rated thermostat for Raw Water cooled is 160 but they run at 175. If your exhaust manifolds and Risers are only warm to the touch when running and your at 175, you got no issues. Enjoy your day on the water.

Thank you Senior B. My concern is that it was getting close to 200 when on plane. I'm not sure how high it would go because I brought it back to idle, where it slowly settled to around 175. Previously, the gauge was pretty steady around 150.

 

[Lou C]

I think when you have a 160 stat you should see this at idle. Pic was taken in the water after cooling down after coming off plane. Maybe a bit higher but based on my experience (only difference is I have a 4.3 with the Cobra drive mounted impeller, but exact same thermostat housing & exhaust system) is if I saw 175 running on land before commissioning the boat I'd be looking for problems.

 

[CapnNemo]

In the drive there are 2 water tube grommets that seal the water transfer tube that sends water up from the lower unit to the upper unit. These can deteriorate over time and cause lowered raw water volume as can that plastic fitting in the pivot housing which can crack. However these factors would cause overheating more so when you’re up on plane where the drive is out of the water partially. The fact that it runs at 175 on the muffs and flush hose on land suggests to me something else. With that same thermostat housing & thermostat my old OMC runs right at 160 on the hose. So I think something else is going on here like the stat is not opening far enough or at the right temp. I usually test them in a pot of water hanging it in the water with a coat hanger wire & an old school auto radiator thermometer. I would check that, and also it is possible you may have clogging in your exhaust elbows if they have never been taken off, checked & rodded out. With a good impeller, thermostat & clean exhaust my old ‘88 4.3 runs at 160 in the water sometimes cooler on plane & the hottest it ever gets is 175 after coming off plane but it soon cools back down to 160. The manifolds & elbows are 90-110 at idle and the hottest they get is 135-140 after coming off plane.
When checking the accuracy of the gauge I have found that the place on the engine that accurately mirrors the gauge reading is the intake manifold right under the stat housing. When the gauge reads 160 the temp there is 145-150.
See if you can find a document called “Volvo Penta Overheat Diagnosis” it is a PDF with all the Volvo specific troubleshooting information you need to track down the cause….

Thanks Lou. I agree that it isn't drive related since I can replicate the elevated temperature at idle using the water port. I have not removed the exhaust elbows since I've owned the boat (~ 1.5 years), and not sure if/when the previous owner did that. I have the document you noted, and will take a closer look. Since the risers don't feel very warm, do you think this is a high priority for me to look at?

I did remove the thermostat, and tested it in a pot of water while heating and cooling the water. It appeared to start opening around 163 degrees when heating, and then was completely closed by about 149 degrees when slowly cooling the water. I had a new thermostat, so I replaced the thermostat, and that didn't change the behavior at idle/fast idle. I haven't been able to test under load yet, but I'm not optimistic.

Thanks for suggesting taking temperature under the thermostat housing. I will check there today.

 

[Lou C]

The other thing that can cause overheating at higher speeds is leaking head gaskets. It explains how to check for this in the document (basically you just replace the manifold feed hoses with clear hose & run it on plane then check for bubbles in the cooling water flow in those hoses) . I had this exact problem it surfaced after a bad overheat a few years earlier. If the engine was never overheated though it’s a small chance it’s that.
These raw water cooling systems (low pressure) need a lot of water IN & OUT anything that gets in the way of that volume of flow will cause overheating.
If your elbows are cool, I doubt you have a problem there. How does the water flow exiting under the transom mount look? Good flow? I’ll post a vid of my Cobra so you can compare.

 

[Lou C]

View attachment Cobra running on the water hose.MOV
does yours look like this, look right above the anode on the front of the outdrive....

 

[CapnNemo]

View attachment 361746
does yours look like this, look right above the anode on the front of the outdrive....

Thanks for posting this! I believe it does still flow from there (and about that much), but I'll look closely tonight. Regarding flow rate, the indications seem to suggest that the flow is good through the raw water pump and the exhaust risers, since only the engine is hot, as far as I can tell. I think your point about having good flow in and out is key. I am trying to understand the circuit that the water takes through the engine. I am assuming that the raw water enters (not exits) the engine through the thermostat housing. If so, then where does the displaced hot water go? It seems that it could be obstructed from leaving. Are there channels for it to go directly from the engine to the exhaust manifold? If so, that seems a likely place for a blockage. Thinking back to your prior comment, perhaps it might be good to remove the risers and exhaust manifolds and make sure everything is clean. On the other hand, if a leaking head gasket results in bubbles in the manifold feed hoses (as you stated), then perhaps I have it backwards. In that case, where does raw water enter the engine?

 

[Lou C]

Here is a pic of the OMC/Volvo thermostat housing (yes they used the same exact part, same thermostat too depending on the year).
The stat housing works like a gate valve. When the engine is cold, the cold water enters the stat housing and flows out the exhaust. The water in the engine just re-circulates till the stat opens, then the hot water flows out from the intake manifold, past the thermostat, out to the exhaust. At the same time, cold water is drawn into the stat housing and mixes with the hot water exiting, but some is also drawn into the engine, to reduce internal temps.

 

[CapnNemo]

Here is a pic of the OMC/Volvo thermostat housing (yes they used the same exact part, same thermostat too depending on the year).
The stat housing works like a gate valve. When the engine is cold, the cold water enters the stat housing and flows out the exhaust. The water in the engine just re-circulates till the stat opens, then the hot water flows out from the intake manifold, past the thermostat, out to the exhaust. At the same time, cold water is drawn into the stat housing and mixes with the hot water exiting, but some is also drawn into the engine, to reduce internal temps.

This is great! Thanks for all this detail! I didn't know about that bypass passage. So, then, the thermostat housing is the only way for water to get in and out of the block (aside from the recirculating pump, which just returns water to the thermostat housing).

I used an IR gun next to the temperature sender and it tracked very closely to 150F (within a few degrees). When the gauge said 175, the IR gun said 157. Given that the temp sender has a pretty nonlinear calibration (I did find one in the Electrical, Carburetor, and Ignition manual), I guess it isn't surprising that the temperature starts to deviate when the temperature gets higher.

But this temperature measurement exercise may have provided some insight into the source of the problem, and it might be very minor. When I started the engine I ran it at fast idle only a minute or so until it would run steady at idle speed (on the garden hose). As it slowly warmed up (at idle speed), I took the temperature with the gauge and the IR gun every 25 degrees (100, 125, 150, 175). But it stopped at 150! So then I increased the rpms to 1200 and it slowly crept to 175 and held there. So, I'm thinking this garden hose result may have just been a red herring. After thinking about it, I'm not sure that I've ever run for a prolonged period at FAST idle on the garden hose -- I usually only run it to bring it up to operating temperature. Maybe that's normal for fast idle on the garden hose.

So, then why did it overheat on the lake? Well, I noticed today that the hose port cap was much easier to tighten than I recall the last time I had it open (before the overheating problem). Maybe cross threaded or something?? It seems likely that I didn't have it closed properly (hand tightened). So it is certainly a possibility that it was sucking air.

I will get it back on the lake for another test within the next couple of days, and I'll report back. If the problem persists, I'll rig up the clear tube diagnostic setup from the overheating manual, and will check pressures and look for air getting into the system.

Thanks again for your help!

 

[Lou C]

My pleasure!

 

[jimmbo]

I would say 175 is too hot for a raw Water cooled engine. My 5.7 runs at 155, and has done so for 20 yrs. The only times it has went higher was when RW Impeller Shredded, and when the Inlets got covered with a Plastic Bag. Both time the Exhaust Temp Alarm went off and I had slowed down by the time the Temp Gauge went up

 

[bruceb58]

The engine likely came with a 140F thermostat.

 

[jimmbo]

Perhaps. I never looked, frankly I never cared

 

[CapnNemo]

I took the boat out for another test drive, and everything was fine. Idle, full throttle, pulling skiers, and everywhere in-between. Pretty much steady around 155 on the temperature gauge. When I was getting high temperatures, I'm pretty sure I was sucking air through the hose port. As I mentioned above, I have a recollection that the cap was hard to turn when I last put it on. My memory is a little foggy, but I think it was dark and I wasn't giving it the attention that I should have. I also changed the thermostat while I was trying to figure this out, but I tested the old thermostat, and it seemed to be doing its job, and changing it didn't seem to make any difference while running on the hose. I also checked the raw water impeller and replaced it because it looked fine. So the hose port seems to be the most likely cause.

Thanks, everyone, for your input. This is an amazing community! I've learned a tremendous amount, despite apparently having such a silly little problem.