Intermittent Over Heating Issues - 2008 5.0 Mercruiser

[Threegpsi]

2008 Tahoe Q8i - Mercruiser 5.0 Fresh Water Only

Engine Serial Number - 1A043597
Transom Serial Number - 1A117233
Drive Serial Number - 0W935097

Impeller was changed before the 2016 Spring Season.

Hello all - Thanks in advance for helping me through this issue. About middle of summer season I would randomly overheat (Typically after start up). The first time I thought I had some trash on the intake so stopped, reversed, went forward and then it immediately opened up and cooled back down. I thought it was a one time thing, but few weeks later it happened again, then it was almost every-time I took it out near the end of the season. I wrote it off to a faulty thermostat and just dealt with the short stop/start/reverse dance till I pulled it for the winter. Well I threw in a new thermostat a few days ago, threw the muffs on and it is still happening.

Does anyone have any ideas or thoughts that I could start troubleshooting?

 

[Bondo]

Ayuh,.... Welcome Aboard,.... In 'bout any overheat situation, the impeller is always the 1st place to look,...

If ya had junk blockin' the water in-take the 1st time, the impeller mighta been damaged at that point,...

 

[alldodge]

Agree, being a bravo drive it should be easy enough to pull the impeller. Being a Gen 7 pump also check the wear plate for groves

http://www.mercruiserparts.com/bam/subassembly/31852/12840/270

 

[Threegpsi]

Hey all - Just an update, I replaced the impeller (Looked fine, no wear), and I'm still having the same issue. No groves on the wear plate either. Anybody of a second guess now that we know it's not the impeller?

 

[alldodge]

Hey all - Just an update, I replaced the impeller (Looked fine, no wear), and I'm still having the same issue. No groves on the wear plate either. Anybody of a second guess now that we know it's not the impeller?

I would start pulling hoses, check the power steering cooler and back flush the hoses. If all check out, next pull the fitting off the transom assembly to check for Bravoits. This is where the line coming from the drive shrinks due to the line swelling. Will look something like this

 

[Fun Times]

2008 Tahoe Q8i - Mercruiser 5.0 Fresh Water Only

Engine Serial Number - 1A043597
Transom Serial Number - 1A117233
Drive Serial Number - 0W935097

Hi there, just for better clarification, How sure are you that your engine serial number is correct being 1A043597? For me it's coming up as an Alpha design engine model but your other two serial numbers are showing it to be a Bravo drive design.

Where is the "impeller" housing located that you changed out?
And do you have a closed cooling system (AKA use antifreeze for the internal engine) or lake water runs through the engine internals?

Yegboats Serial Number double check please.

 

[Threegpsi]

So I ran water through most every hose and seems to have good flow. Is there a certain back flush procedure I should follow?

Yes it is a Alpha with the Bravo drive. Weird combo but yes I am certain on that.

 

[Threegpsi]

Hi there, just for better clarification, How sure are you that your engine serial number is correct being 1A043597? For me it's coming up as an Alpha design engine model but your other two serial numbers are showing it to be a Bravo drive design.

Where is the "impeller" housing located that you changed out?
And do you have a closed cooling system (AKA use antifreeze for the internal engine) or lake water runs through the engine internals?

Yegboats Serial Number double check please.

It is not a closed system it does use lake water. Yes it is the Alpha with a bravo.

 

[Bondo]

Yes it is the Alpha with a bravo.

Ayuh,..... Welcome Aboard,.... Alpha, 'n Bravo are the series of Drives,... It can't be Both, ya got 1, or the other,......

 

[alldodge]

Is your impeller in the drive, or belt driven pump attached to the starboard side of the motor?

 

[Threegpsi]

Is your impeller in the drive, or belt driven pump attached to the starboard side of the motor?

Belt driven

 

[Threegpsi]

Ayuh,..... Welcome Aboard,.... Alpha, 'n Bravo are the series of Drives,... It can't be Both, ya got 1, or the other,......

I copied the serial numbers directly from the 5.0 mag cover. I tried to upload a photo of that but it's not lettting me.

 

[Threegpsi]

http://i565.photobucket.com/albums/s...806612179A.jpg

 

[Fun Times]

Thanks for posting the photo of the serial numbers, you had one number incorrect. You had 1A043597 while it's actually a 1A049597 which makes more sense as the engine is now coming up as an MERCRUISER 5.0L MPI BRAVO engine package to fit your stern drive.
I was just about to send you down a possible path of something that could of been an issue due to thinking you had the wrong type engine cooling system as there is a small difference between the Alpha and Bravo cooling systems all tied into a different size fitting that could cause an overheat situation. In the following link notice item number 20 having one that fits an Alpha engine and one that fits a Bravo engine. If using the wrong one, it's said by Mercruiser to overheat the engine. https://www.perfprotech.com/mercury...temsingle-and-3-point-drain/assembly/8093/200

Now knowing that small fitting could cause an overheat, you may have an internal blockage somewhere in those cooling lines and/or have an exhaust system blockage somewhere which can cause engine overheat too.

Back flushing the cooling line system is a step process you'll want to consider trying along with checking the exhaust system.

 

[Threegpsi]

Thanks for posting the photo of the serial numbers, you had one number incorrect. You had 1A043597 while it's actually a 1A049597 which makes more sense as the engine is now coming up as an MERCRUISER 5.0L MPI BRAVO engine package to fit your stern drive.
I was just about to send you down a possible path of something that could of been an issue due to thinking you had the wrong type engine cooling system as there is a small difference between the Alpha and Bravo cooling systems all tied into a different size fitting that could cause an overheat situation. In the following link notice item number 20 having one that fits an Alpha engine and one that fits a Bravo engine. If using the wrong one, it's said by Mercruiser to overheat the engine. https://www.perfprotech.com/mercury...temsingle-and-3-point-drain/assembly/8093/200

Now knowing that small fitting could cause an overheat, you may have an internal blockage somewhere in those cooling lines and/or have an exhaust system blockage somewhere which can cause engine overheat too.

Back flushing the cooling line system is a step process you'll want to consider trying along with checking the exhaust system.

Thank you for your help!!

So it's possible I have the wrong fitting in there? I have read that a few times and was curious how I would know if that is the right or wrong one?

Also, I think I am going to go back a flush again. Is there a step by step process I should be doind to make sure it is being done correctly?

 

[alldodge]

I've done some looking but cannot find anything on the parts, not even a pic to compare. If we could find someone that has the single point drain and an Alpha drive could post