Volvo penta 4.3l temperature fluctuating

[cnotecherry]

been a while since I have posted here I am having trouble diagnosing a temperature problem my temp is consistently fluctuating it gets up to temp 163* then climes to about 190* for 2 seconds then falls to 150* then back to 163* and holds for a bit then back up to 190* back to 150* and then 163* and so on these readings are from a IR heat gun my temp gauge is a little higher but right on par with the trend this is all at idle these are closed cooled engines I have twin 4.3lGI those were starboard engine readings the port engine is a bit lower readings but is doing the same trend I am 95% sure its in the closed loop both engine have brand new raw water pumps newer exhaust witch I have checked and they are fine newer heat exchanger wich I have cleaned hoses are all in good shape and have no leaks seam to be pumping lots of water my exhaust is ice cold all the time new t-stats did the same thing with the old stats I am thinking the fresh water pumps but find it weird that both would go at the same time both closed loops don't seem to expand the expansion tanks are always at the same level hot or cold I have delt with and fixed many overheating problems but this one really has me stumped if anyone has had a similar problem and can chime in it would be much appreciated thanks

 

[tpenfield]

You did not mention if the heat exchangers are completely full . . . Or not.

 

[Lou C]

Agreed it sounds like air in the system, you might need to use one of the air bleeder funnels that Lisle sells, I have one and it works great.

 

[Scott Danforth]

agreed, check the coolant in the HX

 

[cnotecherry]

That crossed my mind as well because I have had that happen in my old boat but it just worked itself out by running it and adding more coolant how does this air bleeder work? And how does air get trapped in the block thanks

 

[cnotecherry]

I have checked the HX coolant level it's always right full and when it gets to temp not even air pushes through the resivior tube I have a couple spair rad caps and have tried them same thing i never lose any coolant so I don't think its leaking I am going to make a air funnel out of one of the caps and bleed for a while today

 

[cnotecherry]

Well I bled the coolant on my port engine for hours today I did see a bit of air come up through the funnel I made but it did nothing as far as my problem goes it's still doing the exact same temperature swings like clockwork I did notice when I reved it up the temp would go even lower sometimes like 130* ish maybe even lower at times but climes back up to 190* and falls back to 163* and holds for a bit and then cycles through again I also notice when the temp gets colder my risers warm up a bit and when it hits 190* there ice cold like the water isn't cooling anything but the exhaust could a week circulating pump cause this I thought they were pretty bullet proof other than the seals and bearing but maybe a fin or something broke off the impeller but for both engines to be doing the same thing is quite coincidence appreciate any input thanks

 

[dypcdiver]

Do both engines do it in sync or do they do it independently?
If they are doing it at the same time I'd be looking at an electrical problem.

 

[cnotecherry]

No definitely not in sync usauly one will hold rock steady at 163 and the other one will bounce around

 

[cnotecherry]

Dypcdiver my readings are from a IR heat gun so even if they were in sync it still wouldn't be electrical because the cooling system is 100% mechanical system if I was just going off my instrument gauge then it could be electrical

 

[Lou C]

I would do a pressure test on the cooling system and a compression test; to rule out a head gasket starting to leak. We had a similar issue on a 98 Subaru EJ 2.5 but it was pushing bubbles into the recovery tank and losing coolant..

 

[cnotecherry]

Funny I was just thinking that was just looking at radiator pressure testers online but still weird that both engine are identical in temp swings and they're both like clockwork I'm kind of leaning toward a plumbing issue of some kind they have new san Juan HXers when I bought it last year and maybe who ever plumbed them in messed something up I am going to bypass the cabin heaters today and maybe pull and inspect the circulating pump also I was thinking of putting a clear hose for the bypass temporarily to see how much flow there is after I do compression and leak down test to eliminate head gasket but if it was head gasket I don't think the temp would drop 30* below operating temp that's why im leaning towards circulating issue I'm wondering if these engines were originally raw water cooled and previous owner put the SJ closed cooling kit on them and there just a bunch of crud still in the system anyway I have a lot of work ahead of me I will report back with my findings

 

[cnotecherry]

Well made a bit of progress today did a compression test and pressure tested the cooling system all checked out good on both engines thank God did not want to be busting heads off or pulling engines I did solve half my problem I bypassed the bus heaters and that seems to be my problem I'm thinking they were clogged up or they have a restrictor valve or something I was only able to run the port engine and it never got obove 170 but still dived down to 155 ones and a while especially when reved up a bit but for the most part held pretty good usually that would be a thermostat but I don't know in this case might try the old tstat and see what it does might wait until I put it back it the water and put a load on it what do you think? The starboard engine runs through the water heater then to the cockpit heater I just bypassed the heater because I like hot water hopefully it's not the water heater too thankfully I put a deisel heater in it over the winter so I was thinking of getting rid of the bus heaters anyway anybody have any thought on why the temp is still fluctuating a bit? Besides thermostat

 

[dypcdiver]

As you have the closed system cooling I believe the thermostats should be the higher temp ones, that run the engines at around 175 F.
Could it be a slug of cold water from the bus heaters that circulates once the T'stats opens? Are you using an external pump to circulate to the bus heaters or relying on the engine circulating pump?

My raw water cooled engine opens the T'stat at 160 and I do see a slight fluctuation as it opens, then that is where it stays all day since I removed the broken vane from the T'stat housing.

 

[Lou C]

Are the heaters at a higher level than the top of the heat exchanger? If so there is a possibility of trapped air in them as well, you may have to fab up a bleed valve at the highest part of your system.

 

[cnotecherry]

Now that you mention it I think the cockpit heater is higher than the HXer but it doesnt matter any more because I am tarring them out I now have a espar deisel heater in the boat so there just added weight anyways and screwing up my cooling system I have already bypassed them I will be able to run the starboard engine today got a new riser gasket yesterday pulled one off the see the condition it was like brand new. Starboard engines bypass runs through just the water heater now witch is definitely lower than the HXer I'll let you know how it goes

 

[cnotecherry]

All is well I ran starboard engine for a while today and it's doing exact same thing as port engine so I think I'm good they both hold at 165ish and dip down to 155ish every once and a while or when I rev them up I can live with that I hope it works itself out and starts holding at 165 all the time but that's probably wishful thinking anyway thanks for all your input talk to you on the next problem I cant figure out

 

[Lou C]

So what was the cure, was it taking the heaters out of the loop?

 

[cnotecherry]

Yes I guess they were restricting the bypass when I disconnected them I blew through and it was extremely hard to blow through

 

[Lou C]

Good to know!