4.3GL PBYC not reaching operating temperature and starboard exhaust riser overheating

[whitebunnyflock]

There is no way that this won't be a long story so here it is.

This is a Volvo Penta 4.3GL PBYC serial number 4110167965. Since I have had it since spring 2017 it has only been run in fresh water. This is a 1999 model boat. I doubt the previous owner had run it in salt water but you never know.....

I should also note that since I have had the boat it has never reached operating temperature. I put the temperature sensor sender lead to ground and it makes the temperature gauge reach max (so i assume the gauge itself is working). I replaced the sensor itself in the last couple years because i thought maybe it was a faulty sensor. I should also note that I put aviation gasket on the threads of the sensor which I am not sure was the greatest idea. I also replaced the thermostat around this time.

Years ago i had posted that the starboard exhaust riser had overheated and the rubber attached to it to vent the exhaust had heated to the point where it started to smoke. At that time I had taken it to a boat shop and they had put a new impeller in it. So I thought... problem solved. This was in 2017. Spring 2019 I had replaced the impeller again even though it appeared to not need it.

Last weekend I took it out and ran at WOT and not long (maybe 5 minutes) and a bunch of smoke coming off the same exhaust riser lower rubber part (sorry not sure what it is called). This had not happened since 2017 although i have always noted that the starboard exhaust riser is significantly hotter than the port riser. I could keep my hand on the port exhaust riser all day and i can't keep my hands on the starboard exhaust riser for more than a few seconds.

Yesterday I pulled the hose off the t-stat housing as i wanted to run some water through with the garden hose to see if there is a blockage on the starboard exhaust riser. I did note some rust on the port on the t-stat housing, not sure if this could be reducing water flow to that exhaust riser. Some flecks may have come out but hard to say as they appeared as the flecks that came off the rubber exhaust venting but the water came through the drain plug i pulled off and it appeared to flow steady and clear (so i don't think there is a blockage there, but i am no pro at this).

We took the boat out again after i checked this and we ran for a few minutes at WOT and even though the starboard exhaust riser was extremely hot there was no smoke. We ran for a bit at 20-35 miles an hour (top speed on this thing is 44 miles an hour). Again as far as I could tell the engine did not even reach 100 degrees fahrenheit (this is how it has always been since I got the boat with and without the new temp sensor and thermostat).

Steps to fix (i haven't done this yet)
I was thinking about the following steps to see what else I could determine. i am not 100% sure that the temperature sensor (even though it is new) is doing what it should. I was thinking about cleaning the permatex aviation gasket stuff off it as I am not certain good contact is being made (although should it really matter?). I was also thinking about doing the thermostat hot water boil test to see if it is actually operating properly. I would also strongly consider replacing the t-stat housing completely as it is 21 years old and it would be nice to just start fresh (perhaps it would take another 10 or 15 years to get rusty then).

I have also had the exhaust risers off completely in the past and noted some corrosion but I didn't think it would be enough to impact the performance (I put new gaskets in at the time).

I would guess that my t-stat is remaining wide open or else one would think it would reach proper operating temp? Pretty sure I put in a 140 degree t-stat when i replaced it (i did buy it at the boat shop).

Also can I safely assume that the corrosion in the housing is what is leading to my starboard exhaust riser getting so much hotter than the port side?

 

[Lou C]

Your problem is common on raw water cooled engines in salt water; a rust flake is probably from stopping the stat from closing all the way which is why it does not warm up. I would:
take the thermostat housing off and make sure all the passages are open and clear, if excessively rusted replace it. Same thing with the exhaust elbows. And check to see if there were exhaust flappers at the top of the Y pipe, if so a bad overheat will melt them and they can drop down and block the exhaust. VP came out with a service bulletin that said these should be removed. I still have em on my OMC rigged engine (same design and same parts)!
In salt water I’ve replaced the manifolds and thermostat housing every 5 years due to corrosion.

 

[whitebunnyflock]

i had also awhile back removed the burnt and fallen exhaust flappers, when i removed the leg and replaced the two bellows.

Which part is the exhaust elbow?

I am in fresh water so i assume i would only replace the manifolds and risers if they were really corroded?

 

[whitebunnyflock]

ok so i found a couple of things, first my thermostat housing had impeller bits in it that I was able to push out (my mechanic left these bits in here after replacing the impeller in 2017). My stat housing is fairly corroded and I have attached some pictures. Also hopefully this thermostat is installed correctly.....

 

[whitebunnyflock]

another stat housing

 

[whitebunnyflock]

stat housing pic

 

[whitebunnyflock]

thermostat housing picture

 

[whitebunnyflock]

i am thinking that some flake of rust off this housing must have been jamming the thermostat. It looked like there was some rust in the way of the thermostat which I guess would make sense.

it was open a very tiny amount but i guess that would be enough to not allow the engine to come up to temperature?

seeing the corrosion would you replace this housing? especially if it is dropping rust on the stat? I also put the stat into a pot of water and heated it up. It seemed to be operating normally, and it especially came open when i hit 180 degrees fahrenheit (very noticeable at that point). Should i replace the stat as well?

the exhaust elbows are where the hose brings the water into the exhaust risers?

 

[Lou C]

Well the housing does not look bad, you can still use it. The rust also comes from the entire inside of the engine so replacing the stat housing really doesn’t sto this from happening. The stat should start to open at 160, and the impeller bits might have been the problem with the exhaust running hot on one side. So, make sure it’s clean and install a new stat. Then take a garden hose and hook it up to the exhaust manifold and turn the water on (you will need a 3/4” inside diameter water hose to do this) see how much water comes out the exhaust housing (under the transom mount). Then do the other side and compare, should be about the same amount of water. If not then you may need to remove the elbows (this is what most call “risers” but they are elbows, the riser is an extension fitted between the manifold and the elbow for more height if needed). And see if they are rusted enough to cause a restriction. These systems need balanced flow on both sides; if one is clogging all the water will divert to the other side so one will be hot and one will be cool.

 

[whitebunnyflock]

thanks so much Lou, i will try the water through the elbow test tomorrow.

 

[whitebunnyflock]

on other thing, should i just blow out any debris in the housing before i re-install it or is there another way i should clean it? perhaps take a dremel to some of the rust where the stat sits?

 

[Lou C]

I would use a drill bit (by hand not with the drill) to clean the rust out of the ports that feed the manifolds. Same with the intake port that is fed by the impeller. Just get all the loose flaking rust out that you can. Then put in a new stat (OE is a 160* stat) that’s retained by the rubber ring. Yours is not that bad because it wasn’t used in salt 100%.

 

[Lou C]

Remember the elbow is the part that’s bolted on top of the manifold many call them risers but the correct term is elbow cause it looks like one! These will have the most corrosion of any part in the cooling system because the hot exhaust gases and water mix where they exit the elbow (the part of it that’s under the rubber hose). These can look good on the outside and be rotted badly under that hose.

 

[whitebunnyflock]

Remember the elbow is the part that’s bolted on top of the manifold many call them risers but the correct term is elbow cause it looks like one! These will have the most corrosion of any part in the cooling system because the hot exhaust gases and water mix where they exit the elbow (the part of it that’s under the rubber hose). These can look good on the outside and be rotted badly under that hose.

so if the elbow is bad would i also need to replace the manifold under it?

 

[Lou C]

Possibly, can’t tell without looking at it...

 

[Lou C]

Here's a new VP style V6 manifold, and what the sealing surface and cooling passages look like...when you take the elbow off you can see how much rust is in both...but do the exhaust flow test first....you may have fixed it just by cleaning out the stat housing and installing a new 160* stat.

 

[whitebunnyflock]

i think they are basically outputting the same amount of water. what i can tell from listening and watching to the amount of water flow

 

[whitebunnyflock]

your new one looks alot better than what i saw the last time i took the elbow off. But from the amount of water coming out basically being the same (and the port exhaust always stayed cool previously) i think i will probably be good. gonna go clean out that housing now...

 

[whitebunnyflock]

now if i could only get off the manifold intake bolt/plug that i drain every fall. wish i could put a ratchet on it.... do you have any tips for that?

 

[Lou C]

Mine doesn't have the drain on the intake, that is a Vortec thing, is it a recessed square plug, or a hex? post up a pic!