Mercruiser Overheating Problem Solved ,how we troubleshoot with clear hoses Dennis Allen San Diego

Dennis Allen of Affordable Marine Service explains Mercruiser Overheating Problem Solved.
Listen to and watch this short clip on how we traced a very RARE over heating problem where engine runs cold at 60 degrees and up to 195 degrees within 20 seconds then cold again down to 70 degrees then back up to 195 degrees .
Water flow diagram explained and problem has only been seen this one time in over 40 years experience working on daily on Mercruiser engines.
3 short video clips , one showing the problem at the beginning. We installed clear hoses from the Bravo outdrive to watch the water flow while running full speed on the water. Clear hoses installed from the thermostat housing to the manifolds. Thermal Temperature gun readings while under load condition as well as clips showing dashboard temperatures.
Dennis Allen Video clips from Affordable Marine Service in San Diego California from January 2020
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[@nspjiffy7447]

This is fabulous. I did all of these steps short of installing the hose. I'm a chemical engineer and I surmised the problem was with the circulation water pump and I will replace it in the next few days. I am now very confident I have the same problem and if I do, I will be sure to send you photos. thank you so very, very much. You guys are excellent!

[@chrisdohan660]

Interesting you say it's a rare problem. It was actually the only cooling problem I had on my previous boat! Luckily for me, it was very simple to diagnose since the bearing or impeller was making a terrible squealing noise. But the symptoms you describe of water temp reading all over the place is spot on. Thanks!

[@justinkristich8266]

Exactly what my four winns h210 ss was doing all last season! Did impeller and thermostat, still would trigger alarm and go into limp mode.. now I know what the issue is thank you so much for this video!

[@craig659]

Fantastic video series, now that's how you learn how to fix a problem.

[@robertwinterstein6690]

Wow, thanks for the great lesson and thank you for taking the time to share this with us.

[@edwardleopold3572]

Priceless information. Thank you!!

[@androutsosgeorge8798]

Thanks for your amazing videos. You helped me solve the overheating issue of my Bayliner 265. Great job!

[@David-vs8lg]

excellent tip to share, much appreciated...maybe Merc can add it to their TS section of the manuals

[@yachtshotsflorida8547]

Great video! Heading out to check Port water pump impeller. No clear hose but a rebuild on circulation pump should be easy.

[@alexaderreyes5945]

Very helpful video brother thank you god bless you

[@alexcarzola9872]

Wow I am having the same issues with my Mercruuser V-8 with an Alpha outdrive. It gets hot. At 19-24 seconds of this video you mentioned something about a plug. What was that. I will also check the water pump. The boat hasn’t run for 4 months. We just finished replacing the Gimbal Berrings. Thanks a bunch. Excellent video

[@rawebonics9914]

Very good stuff thank you sir for this informational video

[@jaybauer5619]

Very good info!!!

[@pedrocamacho8768]

hello Dennis, i am one of your customers, been to your shop lots of times, my Mercruiser 5.7 is overheating so I found one of the risers very rusted, and I hope that's it. i am in the process of putting in a rebuilt fuel pump and a fuel water separator, hope it will take care of my problems came to your shop but you have way too much work to work on mine. thank you Peter

[@davidbowers5487]

Just adding to the earlier comment I made on the mercruiser 3.0 problem with thermostat. Even though the gauge was reading 160 on the dash I couldn’t the find out why the safety system horn was going off and cutting the proper until I got a Mercury Vessel View system and could see it on my tablet via Bluetooth that digital temp was going crazy up and down right when I fired it up

[@DH-se7ck]

Great video, I'm having the same problem on a 5.0 sundeck. Temperature stays normal while running at high rpm, as soon as idle down temperature shoots up. Like you mentioned I replaced everything and used IR gun all over the engine with unbalanced readings. Also been around equipment for fifty years and never saw a water pump impeller break loose from the shaft. Thanks for the video

[@Comprezzed]

I just spent two weeks reverse engineering the cooling system and everything pointed to flow reversion at the thermostat housing. I pulled the water pump and BINGO slipping impeller. I found your video ONE day after I fixed it. 2006 Merc 5.0 MPI Single Point Drain. Same issue. EVERYONE said "stuck thermostat"....but it didn't make sense to me when I felt the thermostat housing get ice cold with my own hands.

[@felipefuentes360]

Sorry this is kind of off topic but I have a leaking power steering cooler water coming into the power steering pump can I just change the cooler and that will fix it

[@nickb8618]

My proline was doing this bouncing temp all over the last two trips. Replaced the thermostat……. Then ordered a new circulation pump fixed it. Gets up to temp and stays there without moving at 160deg. Before it was bouncing between 100-195 in like seconds

[@davidbowers5487]

I have a 2015 3.0 mpi ect thermostats doing the exact thing and I changed it 2 times and the same thing still.Took it to Bass pro shop (Tracker) and they said it was bad wiring and recommended that to buy a wiring harness (really without even checking the harness) or the computer. I have looked everywhere to find a diagnosis and nothing until I just seen this video and now think that is what it is. Thx for the video it can happen to a 4cylinder too obviously.Maybe Mercruisers have a problem

[@johncasor9698]

i would think one would replace the everyday water pump first and the thermostat.... what moves the water in the engine ??? the pump ... i have seen oil pumps do the same thing spin on a shaft and a gear just pressed on the shaft and it loss oil presser and shut down the engine a large diesel N14 Cummings at about $20 K engine in a large transport for Wonder Bread company...

[@manuelcontreras6319]

I have cuestion I have one Crowline 94 with OMC cobra 5.0 but I turned like 2 days ago and the temperature goes up to 180 its that normal or I need to fix something

[@evanbushong4291]

Mine is over heating when I’m sitting still but good when I’m running open. I’m getting water up but iono if it’s enough. Also hose on water heater (starter side is getting real hot)?

[@xleadskinx]

Where did you get clear hoses?

[@careyhargrove9880]

My hose that goes from the thermostat housing to the circ pump blew out, symptom of bad circ pump?

[@mchaves7663]

Nice trouble shooting!

[@jimhicks5055]

Do any of the 5.7 mercruisers use 2 thermostats????

[@MichaelM...TandTribs]

Hi guys, I have just bought a bayliner 2655,and on its maiden journey, as soon as I put load on the engine, oil pressure rose to max, smoke started to billow out of the engine and the engine stalled... Took about 15seconds... Wondering if you would have any idea as to what that could be?

[@JoseHernandez-bq4zf]

I heard the impellers should be changed out every 100 hrs or every 3 years.

[@salvadorperez3570]

Hi I have a question if anyone can help me I installed head gaskets in a mercruiser 7.4L and everything is good motor starts but I'm having an over heating problem with the antifreeze before the head gaskets were put in it never over heated it was fine but I'm wondering if I did anything wrong with installation I don't have too much experience in this so I decided to do my own so I hope somebody responds and helps me thank you

[@socapaul]

I think I may have found the same situation. With a 2005. Temperature is fine till the boat gets over 20 mph then it overheats.

[@beatricechazwick3996]

This is exactly what is happening to my 350

[@openbox6821]

My boat got hot and started making loud noise

[@MikaHovhannisyan935]

Please send photo

[@ngirardo86]

4 different repair shops AND NOBODY THOUGHT TO CHECK THE WATER PUMP????? Jesus H Christ

[@hydraulics]

On boats that circ pump is generally never an issue

[@procharged67]

I just had the same problem on a 7.4 mpi

[@thomaspaccione7214]

What were your symptoms? I also have a 7.4MPI, I was out today, boat was running fine for a few hours, all of a sudden the hight temp alarm went off, temp was just about 200. As I was looking at the guage it shot down to 100, then quickly went back to 200. It sat at 200 for a few mins, then went back to normal working temp. I went full throttle all the way back to my marina with no problem after it acted up. I was thinking it was the temp sender until I just saw this vid. What was yours doing?

[@procharged67]

@@thomaspaccione7214 same as u just described , you need a new water pump on the engine , take it apart u will see its broken

[@thomaspaccione7214]

@@procharged67 Thanks for replying so quick. I went down to look at it more closely, and there is play in the pulley and there is spatter all over the engine compartment from water leaking onto the belt. I agree, the pump must be the issue. They are a little pricey at 215 bucks from Merc.

[@procharged67]

@@thomaspaccione7214 buy the Sierra pump much better price

[@thomaspaccione7214]

@@procharged67 I did, thanks!

[@ronaldtober9443]

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