Engine Temperature Variation-----Don't worry, or what to check?


Alec A

Alec A

Member
So, I been having a variation between my port and starboard engine on engine temperatures while running.

About a year ago, I had to have the port engine thermostat replaced since after a run I had lots of the closed cooling coolant all over in my bilge.

The dealer replaced the thermostat on the port side 8.2L closed cooling engine. (I don't know which temperature rating one they used if same as when it left factory or not)

During a recent long run, the port engine temp will vary between 152F to 172F, and then decrease. I attribute this to the thermostat cracking open at around 170F, letting in cooler water, the cycle begins again.

The starboard seems to be right at 163F to 165F all the time. The only time to see 167F is after a long run (like 2 hours) and then idling to the slip.

The heat exchanger are flushed after every outing with Saltaway as I boat exclusively in salt water. I have the fresh water flush on the engines. (My dealer said that I must spend a lot on Saltaway---I don't care---there is a reason I flush them after each run)

The boat has 198 hours on the engines.

Dealer says I should have the poppet valves inspected. Anyone else heard of this service? Suggestions to replace the starboard thermostat or don't worry about the variation?
 
So a friend recently discovered one of the rubber water hoses partially collapsed at a bend (it basically formed a crease instead of a proper bend). As a result, one engine was only getting 60-70% of the regular water flow due to restriction.

Not surprisingly, this engine was always about 20 degrees hotter than the other.

$8 for some replacement hose, and both engines have the same operating temperatures.
 
Check your flush hose. Mercruiser routes the hose from a tee, in the intake line up and over the engine. Mine was so tight to the engine that it melted up against the exhaust port, where it connects to the manifold. This caused the raw water pump to suck in some air, and reduce water flow, causing lower pressure and higher temp. Luckily I caught it before it became a major issue.
 
Update and still rying to solve a problem on my boat now going on for over 1 year so I thought I would put this out there and see if any of you have an idea.

Boat is a 2015 350 CBR. Engines are 8.2L ECT Mercruisers with Closed Cooling. I have 203 hours on the engines, and I boat in salt water. All maintenance is done by Formula service dealer who is a Mercruiser dealer.

Background: June 2018---After a day of boating, open bilge to do my religious post boating fresh water flush and see puddle of orange coolant in the bilge on starboard side. Call dealer---he says it’s the thermostat so we replace thermostat on Starboard engine. Their diagnosis was “Coolant Discharge from excessive heat build up causing expansion tank to overflow. R/R Thermostat and Coolant Sensor Cap.”

Summer of 2019 I start noticing that my starboard engine temperature ranges while boating between 147 degrees and 178 degrees, while port engine is steady at 163 degrees. I take videos and send to my dealer. On starboard, you can see the temp climb, and then somehow/somewhere a valve (or thermostat?) opens and the water temp drops back to 147ish and then starts the process all over again. It is a steady climb, fall, and reclimb all while underway—and the port side is perfect at 162 degrees

With dealer, we plan for late fall / early winter service which was impellers, fuel filters, and oil & filters. Dealer says, “The problem on the starboard engine is Poppet Valves.” In January 2020, we change the poppet valves and also new exhaust elbows. Checked the heat exchanger and the heater exchangers are clean as a whistle since I flush with SaltAway after every use. Water pressure is fine.

In February, we test it and determine that the problem still exists.

Covid hits---and not much happens.

During Spring boating with just my wife and me, I am still noticing the temperature fluctuation on starboard engine while port holds extremely constant. (This is annoying.)

I had a haul out this week (July 2020) for bottom paint and for drive service. Given the number of hours I boat, we do outdrive service every other year. And it was 3 years on the bottom point since last update. Since boat is 6 years old, I ask my dealer to check about Bravoitis and inquire to Mercury. So, we planned to take off drives anyway for spline greasing, and we checked gimbal bearings. Since the gimbal bearings were good, dealer says we should take off the water inlet houses from Bravo 3X drives and inspect and install new hoses (there is a Merc upgrade he tells me).

I am at the boat in the boat yard for the last 2 days while on the hard. I am watching the entire process of disconnecting the drives and I see the water hoses come out of both outdrives through the transom. Both look fine with no corrosion, no clogging. Updated water hose kits are installed in both drives

Dealer calls Mercury. Mercury says to check the 22-8M0045363 hose bib assembly https://www.mercruiserparts.com/bam/subassembly/31939/16012/115 which I find out is underneath the engine (and a PITA to get to) which is prior to the Cool Fuel Module. They suspect that there might be some blockage/obstruction in there. My dealer says we can tackle that repair when back in the water (which I don’t know since I always think it is easier to do some of this on the hard when water doesn’t come through the lines into the engine. ) I don’t have through hulls on my boat for raw water cooling as the raw cooling water does come through the outdrives. There are no clogs nor obstructions observed in the outdrives.

Dealer surmises it might be the Cool Fuel Module. He says when we run the boat we can touch the back of the cool fuel module and see if hot which he says will tell him if the cool fuel module is failed (but I have never gotten any codes on any issues from the starboard engine on fuel temperature.) IF, and if it is a Cool Fuel Module, those run about $1300 for the module alone.

So sure, it would be easy to throw parts at it---which I don’t want to do---I want to know why I have this fluctuation. It will be easy to run up the engines in throttle mode at the boatyard when back in the water when they complete bottom paint and outdrive paint on Tuesday and at that time check the Cool Fuel modules to “see if they are hot.”

One friend suggested maybe I have wear in the back of my OEM raw water pump and we should change to the newer style that has the wear plate so the impeller doesn’t wear the housing. (One friend swears by the Stainless Hardin Aftermarket Stainless Steel water pumps.) None of the dealer service techs ever mention wear of the housing so I don’t know if the temperature fluctuation is due to cavitation at the back of the housing.

I don’t know if I have a bad thermostat again.

Looking for any insights that others may have since we have changed a thermostat, poppet valves, and water intake hoses through the transom, and we now are on a hunt and see expedition.
 
First off, did they put the correct thermostat in and in the correct way? Fluctuating temp really seems like a thermostat issue.
If thermostat isn't it, rather than throw parts at it, have you thought of swapping parts btwn starboard and port? I had an issue on my 34PC last year where my port engine suddenly died and would just crank. I swapped a couple parts and figured it out that way. Cost me a couple of hours of my time and in the end bought the correct part.
Maybe the dealer could swap cool-fuels between the motors and then if your temp fluctuation moves to the port motor, you have your answer.
I do not think the raw water pump is causing this. If it was just running hot, maybe.
 
Id agree, swapping t-stats sounds like a quick sanity check Alec. They?re about $30 maybe buy a spare to have on hand and use for the test to save some wrenching on the good motor. Internet lore has it they sometimes come bad out of the box but whats the odds i dunno.
 
Not sure this helps but usually the engine that is used to heat the hot water (if has hot water heater) will run 2-3 degrees hotter. Your fluctuation is much higher.
 
Update as of 8/6

Completed bottom paint, drive paint, and new zincs yesterday. Drives looked great at haul out with zero evidence of corrosion. X Drives and dive service, mercatode, and annodes all doing their job. Was at boatyard during the entire process, even prior week watching mechanics do the drive service. Cleaned a few little crusty sea creatures out of my drive showers to ensure they're open and work as intended. As you will note in the post previously, we checked the water intake tubes in both drives and found no constriction nor any Bravoitis type concerns as I am sure many of you have seen photos posted of before on boat forums. They installed (suppossedly an upgrade with fewer bends) new water intake hoses through the transom.

We ran the boat in the slip and found the temperature variation on the starboard engine still exists. The starboard engine cycles going from about 147-150 through about 178 and then the temps decrease to 147-150 and start all over again. One can observe the gradual rise in temps and then the fall out and the rise starts over again. At 1000 rpm it takes about 20 to 25 secs for the temps to build, and then the fall of the temperatures takes 5 secs or so. (I had previously videoed it with my GoPro and sent the video to my dealer to share with Mercruiser).

So, using an infrared heat gun, we confirmed that the issue is NOT the Cool Fuel cooler. I told the dealer that since no codes or such I would have been suspect that was the issue. I listened as he called Mercury and talked with the Engine Technical Guys. They said it sounds like I have a small constriction somewhere. Mercury still said to check the 22-8M0045363 hose bib assembly. I see that is a pain to get to. Might just take that off and see if there is any restriction--but it is under the engine----had 5 hoses it connects to---and it's no easy task. We've already replaced the thermostat 2 years ago and the poppet valves and now the water intake hoses coming through the transom. Exhaust elbows were replaced in January of this year. CATs were checked and manifolds looked good. Heat exchangers were popped open and looked great due to diligent use of SaltAway after every use.


Dealer and I ran the out in the bay for about 30 minutes so he could first hand see the problem as well and it still exists.

I am glad it's not the fuel coolers. (My port engines runs a constant 163 and that is the one plumbed to the water heater so that not it).

I am going to see what he tells me over the weekend after another mercury call. I am learning more towards the simplier the solution the better---and I think we might go change the thermostat again. Sure, its a number of hours of labor and a thermostat---but maybe the thermostat is bad.

It's just a vexing problem and a pain to deal with. I don't think that I am asking too much to get my boat to be running in the correct condition. Watching the temps vary is not correct---and if i don't address this, someday when I want to sell the boat someone's going to note on a survey and say, "Nah, I don't think so" if you don't address it.

Lastly, I think junior (inexperienced) mechanic didn't adjust the drive trim sensors correctly after reassembling the drives. Dealer saw that and I am not happy. I am now getting a critical error for that and I would like for the boat to not go into guardian mode at some time in the future. The sensors and wires looked great when they were disconnected. Plan on Monday is dealer to have mechanic plug into the system to see the valves for the sensor with respect to position. Dealer goes into the water to attempt to adjust sensor. But if not, crap, we have to haul the boat back out!

Thanks for all the suggestions and listening.
 

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Related Question ? I have a 2017 330 CBR with 8.2 SeaCore, which we just acquired. It has remote engine flush ports on the transom and like you I keep it in salt water during the season. How do I

(a) Flush coolant system with SaltAway while in water given that raw water pickup is on the drives. Could I force it through the flush ports somehow or is there some other way of getting it into the system?

(b) how do I flush these engines while in the water after each use?
 
I don't use salt away, but I flush with fresh water after every use. The fresh water flush line is tied in prior to the raw water pump, so at idle, (which mercruiser recommends) the fresh water is brought up through the pump to flush the heat exchanger etc. If you throttle, up the garden hose may not supply sufficient water flow, so you'd probably get a mix of salt and fresh water.
 
Alec A said:
One friend suggested maybe I have wear in the back of my OEM raw water pump and we should change to the newer style that has the wear plate so the impeller doesn’t wear the housing. (One friend swears by the Stainless Hardin Aftermarket Stainless Steel water pumps.) None of the dealer service techs ever mention wear of the housing so I don’t know if the temperature fluctuation is due to cavitation at the back of the housing.

.
Click to expand...

The Tech should be able to scan the motors while running and compare water pressure numbers between the 2 motors to tell if you have a pump issue. The bravo housings do wear, but your water pressure number will show it.

I'd look more into the thermostat
 
Well, we replaced the thermostat last week with a new one and that didn't fix the issue. Also, i took the old thermostat and tested it in ever increasing water here at home to see if it was opening correctly---and it appeared so. There is thinking that maybe the water temperature sensor is bad. I tried measuring the area right around where the temp sensor is located on the crossover to see if the temp was fluctuating there while the Vessel View was showing the rise in the engine temp but that is easier said than done. We're talking about using my infrared temp gun to measure on the outside of a cast iron piece on the crossover the variation of water temperature on the inside that rises over a 30 sec period and then falls back down over 5 to 10 secs. Plus with the rotating belts and where the sensor is, well, that doesn't see like it's too easy to measure. And it's not going to be easy to swap the port and starboard engine temp sensors as I have to remove the coolant overflow tank to get down in there and move the drive lube reservoir. I will work on it again in the next few days and see what I can come up with. I do notice that the temps on the right side exhaust manifolds run about 15 degrees cooler than the left side manifold. I have already changed the poppet valves on both sides of the engine along with the new bravo 3 water intake lines which were NOT clogged at all with bravoitis. Have changed mechanics. The question might be do I have any blockages in the oil cooler or the power steering cooler but I would think that if I had an obstruction in those than the temp would only rise and not fluctuate. The water pressure doesn't seem to be different between the port and starboard engines and even as I throttle up both water pressures are essentially the same. If anyone has a good diagram of all the water flows and piping on an 8.2L engine that would be helpful as I want to know which lines are going into the heat exchanger are fresh water and which are raw water. Appreciate all the help.
 
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