MerCruiser Alpha 1 running hot

[eriefeelin]

I have a 1990 MerCruiser Alpha 1 5.7 that has been running warmer than normal. I had a new water pump kit and water pickup hose installed in late spring. The temp. was right were it's always been. About a month ago I noticed it was running a little warmer that normal. I replaced the thermostat and it hasn't made any difference.
I was idling in to dock the boat today and noticed it was running a lot warmer than normal. When I got to the dock I put it in neutral and bumped it up to about 1400 rpms and the engine cooled back down in a matter of seconds. Is it possible the circulating pump on the engine is going bad even though it's not leaking any water or could it be something else. The boat has only been run in freshwater and it has about 1050 hours on it.

 

[Uraijit]

Re: MerCruiser Alpha 1 running hot

It's possible that you're missing some vanes off of your water pump. It's also possible (more likely) that your impeller in the drive is wearing out.

 

[eriefeelin]

Re: MerCruiser Alpha 1 running hot

That impeller was replaced this past May. I doubt that it's bad already. The boat is docked and I don't boat in water in less than 5 fow.

 

[achris]

Re: MerCruiser Alpha 1 running hot

Do a water flow test.. It's in the manual... With the hose that comes from the transom (goes onto the thermostat housing) disconnected and in a measuring jug, the engine should pump a certain quantity over a 30 second period... I would be doing that as my first test... That would rule out the water pump... If that's ok, start looking for an obstruction somewhere...

I'll look up the data and re-post for you...

Chris.........

Edit: Found it... It's Service Bulletin 82-4. The first one in the Service Bulletin section at the back of service manual# 4...

Boat must be in the water, not on flushers.
Run the engine at EXACTLY 1000rpm for EXACTLY 15seconds.
For a 1.50:1 ratio leg, the output should be 4.0 quarts (3.8litres)
Do the test 4 times...

 

[eriefeelin]

Re: MerCruiser Alpha 1 running hot

Thanks Chris I will try that test. The place where I buy my parts from said that the circulating pump is alright as long as it's not leaking water. He said that the hoses could be bad inside even though they look good on the outside.

 

[achris]

Re: MerCruiser Alpha 1 running hot

Circulating pumps can loose bits off the impeller and not leak water... Bad hoses would have you overheating when you put power on, not at idle...

Chris..........

 

[BRG25]

Re: MerCruiser Alpha 1 running hot

How old are the manifold and risers?

 

[eriefeelin]

Re: MerCruiser Alpha 1 running hot

They are the originals but 2 years ago I had the risers off to replace the water shutters and from what I could see they looked in good shape. The insides had a little surface rust but nothing major. When I replaced the thermostat there wasn't any rust or sentiment present.

 

[eriefeelin]

Re: MerCruiser Alpha 1 running hot-Update

Re: MerCruiser Alpha 1 running hot-Update

I removed the hose that comes from the transom and it appeared to me that I had good water flow coming from the impeller. I removed both hoses from the thermostat housing and the poppet ball assembly looked alright to me. I removed the circulating pump and it looked ok to me and reinstalled it. I have no obstructions as of yet and the hoses look good.
I used a laser thermometer on various parts of the cooling system and exhaust parts.
The temp. sender showed a reading of 144* at 1100 rpm and about 154* at 700 rpm.
The inlet for the circulating pump was around 156*
The hoses that go to the exhaust manifolds were around 162*
Now the strange part-the top of the starboard side riser was around 100*-102* and the port side was 130*-132* and was noticeably warmer to the touch.
The exhaust manifolds were 180*-192* with the port side running about 10 degrees warmer
I held the laser on the sending unit and when I increased the rpm's from 700 to 1400 it dropped from 155* to 145* in a matter of about 15 seconds. Even though the impeller replaced in the spring I think it may be going bad already. The flow of water at idle was a little weak and as i throttled it up a bit the flow was much stronger. Any ideas?

 

[achris]

Re: MerCruiser Alpha 1 running hot

Poppet balls!!.. Bad news.... Merc have had so many bulletins on those things!!

If you can, replace the 'design II' thermostat housing with the 'design III - Alpha' housing.... You will need a few parts... and you will be removing a couple of hoses...

Download the manual for your engine and have a look at it all...

Service Manual #15 1989-1992 GM V8
http://www-alt.mercurymarine.com/mnetdata/SERVICE/CRUISER/Servmanl/15/cover.pdf

Then download this manual and have a look at the newer system...

Service Manual #24 GM Small Block V8 1998- 2001
http://www-alt.mercurymarine.com/mnetdata/SERVICE/CRUISER/Servmanl/24/24covr1.pdf

Unevenness in elbow and manifold temps is common and normal.

Chris.........

 

[tarheelebbtide]

Re: MerCruiser Alpha 1 running hot

Erie, Ive had the exact same issue on my '92 350 Mag w/ Alpha 1 for about a year now. Anything at or above a fast idle and the temp is right down the middle. At idle, she slowly creeps up in temp. If you figure it out, please post as I've been through my cooling system 3 times with no luck on that one. I just always fast idle!

 

[MikDee]

Re: MerCruiser Alpha 1 running hot

Please check the main water feed hose to the engine at the outside thru-transom plate at the bend, these have a tendency to kink real easy! I've run into this problem before on a few Merc. outdrives,,, there is a special rigid hose from Mercruiser (I believe?) that goes from the leg to the plate to prevent this, I don't think you can use just any hose! Also, there is a specific dimension for it's length, in the service manual that this hose has to be, or it will be a problem. When I hear of overheating on these Merc. I/O's, when there's no other issues with the rest of the cooling system, that's the first place I look!

Personally I've gone so far as to just slip a 45* copper sweat elbow over the hose till it settled at the bend to solve this problem, on one boat. I think it was either 1", or 1-1/4" size?

 

[eriefeelin]

Re: MerCruiser Alpha 1 running hot

Thanks for the replies. I installed a new temp. sender to rule that out. I had the impeller and water pickup hose installed by a reputable shop. I'm sure they used the pre-formed pickup hose as they charged me $22 for it. When I pull the boat for the year i'll check the hose to make sure it's not kinked and might inspect the new impeller just to be safe. Guys on different boards said my temp. readings are fine and nothing to worry about.

 

[MikDee]

Re: MerCruiser Alpha 1 running hot-Update

Re: MerCruiser Alpha 1 running hot-Update

The flow of water at idle was a little weak and as i throttled it up a bit the flow was much stronger. Any ideas?

This is what I mean, although at idle the flow would normally be a little less anyway, but if under normal operation it's running a bit hotter then normal and all else in the system seems to be working properly, check that hose.

 

[Jim Krawiec]

Re: MerCruiser Alpha 1 running hot

Hello Folks:
I'm brand new to the forums. Merc running hot! I just compleated a winter overhaul of my 5.7 merc /w Alpha1 gen 2. I was getting an intermitting alarm when I was running my boat. Operating temp was ok, oil ok, drive lub ok, etc.
Check all of the hoses all ok, droped the lower unit all ok. the right manafold
was hotter than the left manafold, pulled the hoses off of the stat where the ball valvs are located, they looked fine untill I started to push water thru them
It seamed that the left ball wasent allowing enough water thru. after pulling the valvs out and giving the parts a good inspection I found chafing on the valve shaft. the left ball valve was hanging up and causing the intermitting water flow. repaired system and everyting is now working fine.
Iboats is a great place to get info.
Thank you
Jim

 

[achris]

Re: MerCruiser Alpha 1 running hot

Hi Jim,

Welcome to the forums....

I tried telling them that (about the poppet balls) earlier, but.... nobody listens... Thanks for your info... I'm sure the OP will be happy about it....

Chris.........

 

[eriefeelin]

Re: MerCruiser Alpha 1 running hot

Hi Chris, I took the poppet ball assembly out and cleaned the balls and springs with degreaser. I took a Scothbrite to the shaft and got it real nice and shiny. When I put it back together I used the fresh side of the poppet balls against the housing and put it back together. I even reversed the shaft so that the nut side of the shaft was on the port side.
With the boat at the dock it seemed the port side elbow runs about 12 degrees hotter instead of 20-30 degrees. The boat also did hold steady at a cooler range on the gauge. Hopefully this wind lays down tomorrow and I can get out. I will run my laser temp. gauge on various parts and see how it is. Thanks

 

[achris]

Re: MerCruiser Alpha 1 running hot

It's quite normal for one exhaust side to run hotter than the other, particularly on flushers. No back pressure on the exhaust so the water will go the path of least resistance......

Chris.............

 

[eriefeelin]

Re: MerCruiser Alpha 1 running hot

The boat is in the water tied up at my dock. That's where I have been working on it. I want to take it out in the lake and give it a try but there is 3-5 ft. waves out there now. Maybe Saturday.

 

[eriefeelin]

Re: MerCruiser Alpha 1 running hot

If I put the laser thermometer right on the temp. sending unit and say it reads 155 degrees there, should my gauge on the dash be reading 155 degrees. The gauge on the dash just reads from hot to cold so I'm trying to get an idea.