Volvo Penta 5.0 GL PWTR - severe overheat - thought I was on fire - troubleshooting Questions

Thanks all. I will look into the magnaflux service. I sprayed wd-40 over everything to keep the rust down while I wait on gaskets, so I suppose I'll need to get that cleaned off before testing.
Great point about the exhaust ports in the center.
My metal straight edge seemed to slide right across with no gaps, but .003" is really small. Thanks ESG for the links as well.
I did find one crack in a bolt hole - see red circle in image "head 2". Thoughts on that?

Also, the surface on both the block and heads between both center cylinders is more worn than other areas, so much that you can't make out the outline of what looks like a cylinder sleeve?

Goose,
Once you decide on the level of cash you are willing to spend it will dictate what you do. Back in post #14 your concern was not dumping lots of $ into this boat. No issue with that whatsoever. This is why I was suggesting look for any obvious issues (like that crack) and if none go for it.

The more you inspect the more opportunity for spending $$. Assume you do the magnaflux and find cracks and the shop recommends not using that head. Are you going to get another head or does that bust the bank you are willing to spend? I’ll say it differently: if you do not know about the crack (that the shop would say is a no go) and you put it back together and get two more years out of it, good for you. Of course, the alternative is that it does become a problem.

So, the other side of the coin so to speak is this: are you willing to put your labor into it with minimum cash and if it does not work you are only out your labor so it’s OK. And heck you could still rebuild it properly from there. If go for it you are looking at only the cost of a set of gaskets and whatever was needed to be replaced due to the overheat. Note: use marine gaskets.

To be clear I am not advocating the short cut. I am just asking you to think thru this.

As an alternative to magnaflux that you can do yourself > dye penetrant. Here is the product (link) and a how-to video (link). Its nasty stuff so wear gloves.

For that crack. It is in the best spot possible > it does not intersect the combustion chamber, and it goes into the bolt hole. Note: when repairing cracks, the first step is to drill a hole at the end of it > this will help it from growing as the stress ‘warp arounds’ the hole and become less.

Thanks. My plan is to sell the boat once it is repaired, proven reliable and running well as I'm already purchasing a new-to-me used boat. I will not pass on a problem to someone else, so I'm trying to choose from a few reasonable options to repair it.

Now that I found that crack, continuing on with that head probably isn't reasonable, but I wanted to get a 2nd opinion from the forum. And if I'm replacing one head, should I go ahead and do the other as well?

I'm not opposed to spending $1k or a bit more on two remanufactured heads to ensure the boat has several good years in front of it with a new owner. I won't put a new engine in it as the juice is not worth the squeeze.

I suppose I'll go forward with finding two replacement heads unless there's a different suggestion.

Thanks all!

Good on ya for not wanting to pass along hidden issues. So, I would do this:

• Dye Pen the block > this way is stays in the boat (less cost) and provides a reasonable check for cracks. If found, post pics as It may be too detrimental to put on remain heads, ie now selling the boat with a busted motor.
• If block ok, do 2 remain heads and put back together. Have some fun and prior to selling do a compression test as a show of “all is good” to buyer.

Also suggest seeing what Lou and others think before taking any action.

The advantage of having a machine shop checked the heads is that they will remove all the valves and that will reveal cracks you’d never see otherwise. My overheating happened in July of 2013, after this it ran perfectly normally you’d never know that there were cracks in both heads! I was seeing sodium in the oil analysis though even before the overheat. At that time before the overheat; I had seen the sodium & also wear metals (Fe & Al) starting to rise. So even before the overheat I think the HGs were starting to leak. Sodium in this case was from salt water cooling. After the overheat, still no sign of water in the oil. Then in Aug of ‘16, difficult starting and rough running, inspection revealed water in the oil and in 2 cylinders….
Since repairs were done in 2017 I’ve done 3 oil analyses and sodium has been on the typical range for marine engines and wear metals have come back down to normal.
Here's the Blackstone Labs reports going back to 2011...


Note: last report was done in 2024, this is when I changed from the regular Merc 25/40 oil to the Merc syn blend 25/50 oil, you can see that it definitely has more zinc and phosphorus than the conventional and holds its viscosity very well. 1242 PPM zinc is even more than just about all the diesel oils. Very expensive though but to me worth it. Remember the short block on this engine is original!

PS here's what a reman head looks like (4.3 V6, pre-Vortec)...


I think what you're seeing is the residue of the old head gasket
Also in this pic you can see one advantage of the V6, none of the exhaust valves is right next to another, I guess it can run a bit cooler under high loads, than the V8.
It also points out another advantage of closed cooling, a pressurized cooling system maintains even temperatures better than un-pressurized open cooling (raw water cooling)....

Opinions on quality of heads from Marine Engines 4 less? They seem to have good reviews online.

Aftermarket - https://marineengines4less.com/5-0l...er-volvo-penta-applications-years-1997-newer/

They don't offer a remanufactured option in 5.0, only 5.7.

Alternatively Jegs offers remanufactured automotive heads - https://www.jegs.com/i/ATK-Engines/059/2CM2/10002/-1

I've read that the valves and springs for an automotive setup are not heavy enough and designed for the way marine motors are run - anyone have an opinion on this?

Augoose said:

Alternatively Jegs offers remanufactured automotive heads - https://www.jegs.com/i/ATK-Engines/059/2CM2/10002/-1

I've read that the valves and springs for an automotive setup are not heavy enough and designed for the way marine motors are run - anyone have an opinion on this?

Click to expand...

Ayuh,.... Nothing "Marine" 'bout 'em,....
Same as heads used on pickup motors, which are the same as standard production automotive motors,....

Bondo said:

Ayuh,.... Nothing "Marine" 'bout 'em,....
Same as heads used on pickup motors, which are the same as standard production automotive motors,....

Click to expand...

Perfect thank you sir. I'm leaning towards the remanufactured solution

the only difference between your boat motor and a truck motor is the head gasket, the core plugs, starter, the cam and the raw water pump. the ignition and induction were added by volvo along with the exhaust.

your "marine" flywheel is nothing more than a GM manual transmission flywheel.

the exact same short block and heads were pulled off the shelf as the pickemup truck motor going down the assembly line

fact. GM's Tonawanda engine plant made nearly all the boat motors for a year over a 2 day period, then went back to truck motors. that is how small the boat volume is to the truck volume.

later truck motors and industrial motors (your marine motor is an sub-set of the GM industrial motor line) used the same head gaskets and core plugs, so that minimized the changes

the truck motor cam is even really close to the boat motor cam.

Scott Danforth said:

the only difference between your boat motor and a truck motor is the head gasket, the core plugs, starter, the cam and the raw water pump. the ignition and induction were added by volvo along with the exhaust....

Click to expand...

Thanks Sir. I did order head gaskets based off the VP part number, so I should be good there.

Unfortunately the remanufactured heads from Jegs won't ship from the manufacturer until July 29th, so I'm not waiting for that. I can't find any other remanufactured options online so I'm inclined to go with Marine Engines 4 Less and purchase two of their aftermarket heads.

Thanks all

Ok, here's the update. I finished installing new cylinder heads with all new gaskets on all associated components, new temp sending unit, new temp gauge, and a new 160 degree thermostat. I started the boat on muffs at idle and it sounds good. I bought an Amazon laser temp gauge and took readings for about 8-10 mins at the following locations (all fahrenheit) and at idle:
Thermostat housing - 132
Hose from Impeller to thermostat housing - 100
Hoses from thermostat housing to manifolds - 132/135
Impeller housing - 86
Top of left exhaust riser - 196
Side of left exhaust manifold- 220
Top of right exhaust riser- 193
Side of right exhaust manifold-195
Intake manifold near temp sending unit - 131
Top of temp sending unit - 132
Temp Gauge on dash read- 175
Left and right Exhaust elbows - 160

While idling on muffs, the engine felt hot but it might just be my paranoia. I kept waiting and waiting for the thermostat to open and cool down the exhaust risers and manifolds but it seemed that the thermostat never opened so I stopped the motor.
If the thermostat housing is still below 160, assuming the thermostat hasn't opened yet, is it typical for the manifolds and risers to be in the 220 degree range?
While I'm testing, what's the max temp I should let the exhaust risers and manifolds get to before shutting the motor off?
Thanks!

I think your temps are normal except for the manifolds & elbows, I think thats higher than it should be…my Cobrs has the same Volvos style exhaust system and in the hose at idle runs about 95-100* for the manifolds & elbows. The only difference is the Cobra has the impeller
In the drive vs on the engine like the Volvo but I don’t think that should make a difference. How old is your impeller? Do your muffs fit well? Even on the water the hottest they get after running on plane is about 135-140* depending on where you take the reading.
Congrats on getting the job done!

Thanks Lou. The impeller is new and the muffs fit very tightly. Three weeks ago when we tested the boat in the water (when head gaskets completely failed) the gauge on the dash appeared to show almost 210 before all of a sudden the engine temp dropped drastically down to 160 or so. At that time the risers and manifolds became cool to the touch. Its almost like this new Volvo Penta thermostat housing and thermostat respond super slow......
As I was writing this I pulled up the listing for my Faria gauge. To add to my confusion, this gauge is confusing to read. The red line indicts where my needle was earlier today at idle. I interpreted that to be around 210 Fahrenheit based on how close it was to what I thought was the "250" white tick. However, 80 degree Celsius is around 176 degrees Fahrenheit and 120 degrees Celsius is around 250 degrees Fahrenheit, so the two white ticks to the right and left of 80 don't correspond to 100 and 250 degrees Fahrenheit. Based on this assumption, if the needle were where the red line was it seems it would be about 185 degrees or so?
Regardless, it does seem my risers and manifolds were too hot.....if the engine was only getting to about 185 or so when I stopped the motor, why are the manifolds and risers getting so hot?