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Jason
Jason, Marine Mechanic
Category: Marine Electronics
Satisfied Customers: 14292
Experience:  Degree in Marine Technology, Also Certified with Mercury Marine, MCM, MIE, VP, Yamaha, Honda, Suzuki
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I have a cooling issue with a 2004 Vvolvo Penta 5.0 GL-D

Customer Question

I have a cooling issue with a 2004 Vvolvo Penta 5.0 GL-D
Submitted: 23 days ago.
Category: Marine Electronics
Expert:  Jason replied 23 days ago.

Hi David, my name is Jason.

Is the engine actually getting hot? Have you verified the temps with an infra red temperature gun, or are you relying on the boats gauge?

Customer: replied 23 days ago.
As gauge approaches 200 F - hose in recirc loop is very hot to touch. Also, alarm goes off, which is a separate sensor on top of the thermostat housing. 2 separate gauges indicating high temps, so yes, confident gauges are indicating correctly. But no IR gun reading.
Expert:  Jason replied 23 days ago.

Got it. Are you using the sterndrive for a water pickup, or does the boat have a through hull style water pickup?

Customer: replied 23 days ago.
Volvo Penta 5.0 GL-D with SX outdrive, so sterndrive water pickup design. And I confirmed it works properly by disconnecting hose after impeller and seeing water flow 2 inches high at engine ht (befoire it would connect to engine. So we know water is getting to engine. And we know water is leaving the block as I disconnect 2 hoses and observe good flow to risers.
Expert:  Jason replied 23 days ago.

When was the last time the bellows, and more importantly, the water line in the transom have been changed out?

Customer: replied 23 days ago.
Bellows changed out 3 yrs ago. Transom line never in 12 years. But good water flow observed from hose after impeller (just before engine block). If bellow/transom issue, then no/low flow would be observed after impeller. Not the case here.
Expert:  Jason replied 23 days ago.

When you say not the case here did you actually put a vacuum gauge on the inlet of the seawater pump and a pressure gauge on the outlet of the pump and observe both your vacuum and pressure when under load, and when the engine is overheating?

Expert:  Jason replied 23 days ago.
I'm attaching a picture, see attachment. Did you do as is shown in the picture, or somehow come up with another way to measure both pressure and vacuum? (see attachment)
Customer: replied 23 days ago.
No vac gauge or pressure gauge. Just observed good flow at idle and assume good flow at high temps. Never checked at high temps as don't want to take water from engine. Any reason to believe flow would decrease with rpm? Wouldn't flow be higher since impeller spins with rpm?
Customer: replied 23 days ago.
I also attached fresh water hose to intake - it T's just before impeller to flush system. Same high flow rate so deduce no inlet issues.
Expert:  Jason replied 23 days ago.

The reason I am asking all of these questions is because that water line in the transom should be changed every 5 years, when the bellows are changed. 2 things happen with that hose over time. The first is it structurely delaminates. It simply falls apart over time, and they can develop a bit of a flap on the inside of the hose, causing a restriction to flow. The other thing that happens is it simply gets soft over time. There are 2 sides to the seawater pump, an inlet and an outlet. The outside side is always under pressure, but the input side is always under a vacuum. The higher the engine RPMS are, the higher the pressure on the outlet side, but there is also a higher vacuum on the inlet side. The water line can only take so much vacuum until it will want to start to suck itself flat, and I say that assuming the line is just old and soft, and has not actually structurally failed yet. What we would do in the shop to confirm this is pretty much what you see in the picture I gave you. We would hook up pressure and vacuum gauges on the seawater pump, run it, and watch the vacuum. Vacuum will slowly increase with RPM as it should. But what we are looking for is to see if vacuum is excessively high, or if it jumps quickly. For example, if it's holding a steady 2 inches of mercury at 3000 rpm, but it jumps to 7 or 8 inches of mercury once you pass 3500, what you are seeing is that hose either sucking flat or structurally failing. The water line would be the next place to go on this problem. If you brought it to my shop while the water line is getting changed we would try and force water backwards through the sterndrives internal water jacket to see if there was any kind of blockage in the sterndrive as well. Being 12 years old the line is clearly overdue. Does that all make sense to you.

Expert:  Jason replied 23 days ago.

I don't know how you want to leave this but that is where you stand on your end and what needs to be done. I think that should do it but I work for tips so I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Questions do not close out, so if you have to come back later on with follow up questions to the issue you still can even after doing a rating.

Thank you
Jason

Customer: replied 23 days ago.
Makes sense. Which is why I would not see it at low rpm. I will plan to change the transom line since it is way overdue.What about the 2 outlet hoses to the risers? They seem cool while the recirc hose is hot - definitely different temperatures by touch. If little water was getting to the engine, wouldn't the recirc hose and the 2 outlet hoses be the same temp?
Expert:  Jason replied 23 days ago.

The exhaust system should always normally be cooler than the engine temperature, so that you are seeing is normal. The exhaust system gets what they call bypass water. Bypass water is water that bypasses the thermostat. Your seawater pump has an outlet. If you follow the hose off of the outlet the water flow spits. One side of that split goes into the engine block, but it must pass through a thermostat before going through the block first. The other side of the spit goes right to the exhaust system. The water going into the exhaust is the same temperature as the body of water you are floating in, the water going into the engine has to go past the thermostat first, which is why it will always be hotter.

Expert:  Jason replied 23 days ago.

Was there anything else?

Customer: replied 23 days ago.
when the thermostat is open - as when I am at high rpm - the inlet water should go through the engine (helped by circ pump) and out thru thermostat. But when water flow is low - as you suspect - then all of inlet (that small amount) would go to engine and come out very hot, right? And the outlet hoses at low flow should be hot, right?
Expert:  Jason replied 23 days ago.

I'm having a hard time understanding what you are trying to say. Is there any way you can reword that?

Expert:  Jason replied 23 days ago.

Are you still here?

Expert:  Jason replied 23 days ago.

It looks like you read my answer without replying back or putting through a rating for me. Please keep in mind the website did charge you to speak with me, but they will hold your money and not credit me for helping you out if no rating is put through. If you have a further question on the issue by all means please feel free to ask. If not, kindly select a rating for my service. If you have a problem with the ratings box or can not see it please let me know.

Thanks

Jason

Customer: replied 23 days ago.
we are on the same page with flow. 4 openings on top of engine. 1 is inlet from impeller - always cool. That water can go to engine or bypass to risers hoses (2). When the engine is cool, water stays in recirc loop as it cannot escape closed thermostat. And so all inlet water bypasses engine to hoses to risers. When the engine heats up and the thermostat opens, engine circ pumps water from engine out from loop, and takes in water from inlet.When inlet flow is low (what you theorize), and engine is hot, the little bit of inlet flow goes directly to engine - no bypass - and little bit of flow goes out of engine to hoses to risers. That water to riser hoses should be very hot water - almost as hot as recirc hose since no cool water available, right?But my hoses to risers are NOT nearly as hot as engine circ hose. Which is why I am looking for help.
Customer: replied 23 days ago.
I will change out transom hose - that is a good idea. Should I be concerned about blockage in manifold/risers since 12 years old? 100% in fresh lake water - no salt. And internals did not look gummed up. See pics, attached.
Customer: replied 23 days ago.
How often do you find weak hoses while testing boats? Is it common after so many years?
And thanks for your help.
Expert:  Jason replied 23 days ago.

Water gets pushed out of the thermostat from the bottom up. Water leaves the seawater pump and goes to the thermostat housing. That housing is also a water distribution manifold. When cold water goes in, some of that water splits off and goes right to the exhaust system. The other part of the cold water gets sent down to the circulation pump. The circulation pump then pushes that into the block. From there the water doesn't go anyplace until the thermostat opens up. Once the thermostat opens up, water then gets pushed from the engine block, through the thermostat, and back into the thermostat housing. This water is now hotter than it was when it went in. Part of this hotter water gets sent to the exhaust system, part of it gets pushed back down to the circulation pump again and the process starts over.

I see the pictures, the manifolds and risers look clean enough to me. As far as weak hoses go, it happens all the time, the Mercruisers are worse because they use a cheaper grade of hose. What we recommend to our customers is to replace hoses before they actually fail. If you wait until they fail then the expense goes up. For example, on your bellows. It's no real extra work to change that water line when doing a bellows job, so it gets done then, before the hose fails.

Expert:  Jason replied 23 days ago.

Was there anything else?

Expert:  Jason replied 23 days ago.

Was there anything else David? Are you all set or did you have further questions on this?

Expert:  Jason replied 23 days ago.

You did thank me and I was glad I could help, but thanking me does not pay me. In order to credit me you must select a rating from the ratings box at the top of the screen. You can still reply back later of with follow ups if you need to.

Best,

Jason

Customer: replied 22 days ago.
Hi Jason-
Had to take a break. Can I change the transom hose without taking off the outdrive? The transom hose has never been changed - the bellows are only a few years old. Bellows are not due for a few years.
Expert:  Jason replied 22 days ago.

Unfortuantely no, the outdrive and also the bell housing that the drive bolts to has to come off in order to change the line. That's why we always do it whenever we do bellows jobs for our customers, it's maybe an extra 10 minutes to change that water line when it's all apart plus the cost of the hose.

Customer: replied 22 days ago.
Another way to check will be to screw on a vacuum gauge to the fresh water flush inlet. If that shows decrease in pressure, then the problem is confirmed. If not, we still have a mystery but I saved myself 3 hours of work with an early bellows job. I will let you know over the weekend.
Expert:  Jason replied 22 days ago.

I didn't realize you had a freshwater flush system on your boat. However, what you just wrote may or may not be true depending on exactly how your freshwater flush system is plumbed into the boat. Some are plumbed in after the seawater pump that way you can push water through the engine with the engine off and not running.

Customer: replied 22 days ago.
My fresh water inlet T's directly into the intake to the impeller pump. So it will show any pressure drop. I am not excited about replacing the transom line but glad to do it if that solves the problem. First, need to confirm the problem.
Expert:  Jason replied 22 days ago.

Ahhh gotcha.

Customer: replied 22 days ago.
Hi Jason-
Hooked up the vacuum gauge. Read ~3 while idling, up to 10 at full speed. Temp gauge still reached 200 F, no alarm, but shut it down quickly. Risers felt cool the whole time. Circ hose got hot, but that's supposed to. What think?
Expert:  Jason replied 22 days ago.

10 inches of mercury is way to much. The water line is collapsing in on itself.

Customer: replied 22 days ago.
Gauge max is ~30 (during use I only read 10). What should be the max with a good inlet line? Will I see the line collapse? Will it be soft afterward?
Expert:  Jason replied 22 days ago.

There isn't any specification for something like that, but I can tell you 10 is to much. Remember yesterday when I wrote "For example, if it's holding a steady 2 inches of mercury at 3000 rpm, but it jumps to 7 or 8 inches of mercury once you pass 3500, what you are seeing is that hose either sucking flat or structurally failing"

Customer: replied 19 days ago.
Hi Jason-
I found the documentation for "Volvo Penta Gas Engine Overheating Diagnosis" which had the exact picture you sent me earlier. One the following page, it states: "Pressure and vacuum readings should be taken with the vessel moving at idle and at 3000 rpm’s. If equipped with an SX-M or DP-SM drive, readings should be between 2”-19”hg (vacuum) on the inlet and between 2-10 psi on the outlet (with the low reading being at idle and the high at 3000 rpm’s)."
As the vacuum reading for my SX drive was 10" - midpoint in the acceptable range - and did not jump up dramatically during cruise, I am now thinking the problem is elsewhere. That the risers are not getting hot at high rpm also suggests in-flow is not an issue. If intake flow was the issue, everything would be getting hot at high rpm, risers included.
I am thinking the engine block is the issue, and recent low-water conditions may have contributed to sucking up sand. I will remove my new circ pump and back-flush the block. Should have done that anyway before installing the new circ pump.
Does this all make sense?
Expert:  Jason replied 19 days ago.

I've given you 2 hours of my time for absolutely zero pay to me. Not one penny. I would still be looking at the water line. But that's just my opinion based on my experience and your description of the problem.

Customer: replied 17 days ago.
Hi Jason-
We shared symptoms with another expert who advised we pull the circ motor off and backflushed the block. Loads of sand came out. We reassembled, took the boat out, and no longer have overheating issues.
I cannot rate you highly because you misdiagnosed my issue and gave me incorrect information (range of intake suction is 2-19" not 10" you said). Since we arrived at the solution that you never suggested, I do not feel I should pay anything. I dislike giving low feedback, so please advise another way for me not to have to pay without giving honest feedback.

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