Will groove in impeller housing cause overheating?
 

My closed-cooling 5.7 EFI runs about 160 degrees at idle, as I accelerate the water temp rises and seems to hold steady with speed/rpm. At 3500 rpm the temp will rise to almost 200and hold there; about 185-190 at 3000 rpm and 175 at 2000 rpm.

The boat is new to me, so I suspected the impeller. Replaced with a new merc unit but the old one looked like it had very low hours. There is a visible but very shallow groove worn into the plastic one-piece impeller housing, not around the circumference but worn into the end of the housing opposite the steel wear plate. It seemed very slight to me so I didn't replace the housing. I also removed the end caps on the heat exchanger and cleaned out all the tubes with a coat hanger and wire brush (some were blocked with pieces of old disintegrated zinc anode and I thought that was my problem).

With new impeller and cleaned heat exchanger the boat exhibits the same symptoms.

Would the slight groove in the back of the plastic impeller housing cause this or do I need to be looking for something else? What is the logical progression of troubleshooting? Thermostat next, or circulation pump or exhaust manifold risers or what? Engine is bone stock with 500 hours, 2000 year model.

Thanx for any advice!

I dont think the groove would cause this. i would steer towards thermostat. Then move onto checking passages even though it is closed cooled.

Agreed. :cool:

I would not say housing can't be the problem. of course depending on depth of groove... but when I see a groove, I change it, cause it was my problem once...

i would replace the housing anyway, i had a similar problem and it ended up being a small piece of the housing that was missing. In one of the holes for either intake or pressure there is a little rib that the impeller rides on to clear the opening that was gone. You'd never know it unless you held them side by side. After a season of fluctuating temps and several impellers on my port motor i just put a whole new assembly on it. While i had everything apart i compared them and made the discovery. Been perfect ever since.

Had a similar temp problem on another boat that would be nice and cool but as i got higher in the rpm range temp would fluctuate and set my temp alarm off. Turned out to be a slightly loose clamp on the hose on the intake side of the pump allowing air into the system.

Thanks for all the advice, everybody. I count two votes for and two votes against, but glassdave's post makes me think maybe I should go ahead and replace the housing.

How on earth did you determine you were sucking air? I can't begin to imagine how to troubleshoot that, especially since I can't get down into my engine compartment while under way.

Check where the water inlet goes throught the gimbal housing. The plastic fitting gets crushed with corrosion and restricts the water flow. This happens alot if the boat is kept on a lift or out of the water.

I would say you have rocks or trash in the heat exchanger. There will be small holes in the cooler and take a rod and go down through each of them, Remove the end caps on the heat exchanger,And clean out the ends. Check if you have another cooler and look inside it. You probably will find some impeller pieces blocking it.

I read of this phenomenon in another thread. This is my first sterndrive so I am just learning my way around it; how do I check this plastic fitting? Pull off the hose from inside the boat, or do I have to pull the drive off the transom? Thanx for the tip!

During my initial troubleshooting I did remove the end plates from the heat exchanger to inspect its condition. I found several tubes blocked with bits of the zinc anode which had been left too long by the previous owner and had disintegrated. I cleaned all the tubes but the overheating symptoms remained.

Your suggestion to check other coolers seems a good one. I will check and clean the power steering cooler and the fuel cooler next; hopefully there is some debris blocking water flow in one of those coolers. The impeller I replaced was in perfect condition but who knows what may have happened to previous units.

It was actually kinda by luck. I had just started having trouble with the temp in that motor and had an infrared temp gun with me, when the alarm went off the temps were still within reason, warm but under 190/200 so i wasn't cooking anything but she was warming up. I shot the block and heads found the heads normal and the front of the block hot. So i determined it was sucking air from somewhere, it also only got hot when running above about 2500rpm, idle would usually cool it off for the most part. At that point i just started checking the suction side of the pump and found one hose was just slightly loose enough to bubble the stream.

Definitely replace the housing, its a cheap way to eliminate that part of it and if the problem remains look elsewhere. Check all the hoses as well, the loose one i had was snug but you could rotate it with your hand. Tightened it up and problem solved,

The housing problem i had was a real puzzler. I had replaced the impeller in that motor two or three times that year and figured it was caused by sand or gunk being ingested, we have shallow mucky rivers here and i have Merc HP's with only the low water pick ups. I looked the housing over each time and you could not tell anything was wrong with it. It wasnt until i decided to put a whole housing on it that i held two side by side and made the tiny discovery. Its just a small plastic runner piece across one of the openings that was missing and it allowed the vane to flex into the opening and wear out in a short time.

Update:

I replaced the impeller housing and wear plate with no change in overheating symptoms. I replaced the thermostat with no change in overheating symptoms. I R&Rd most of the hoses and checked them and the power steering cooler and fuel cooler for blockages with no blockages found.

After hearing about 'bravo fever' from you guys, I was able to remove the hose and elbow at the transom to see/feel that the plastic insert inside the hose was collapsed. I could also see that the drive would have to be removed in order to change that insert so I took it to a shop to have that done. The mechanic said there was a 1/4" of corrosion between the outside of the plastic insert and the inside of the hose, which had collapsed the plastic insert. He replaced the hose and the insert and I got the boat back last week. We took it out on Friday and it ran perfectly, never getting above 175 degrees all day.

Thanks to everyone for all the advice!

Exhaust risers can be a factor in overheating (maybe not the problem in this case). With saltwater use I had to use a coat hanger to clean mine, between the stainless steel exhaust tube and the cast iron exit, every season.

do your temps start droppng back to normal after a run,,if so then i would agree with bowtie also,,,is this a salt run water boat??

Do you have stock iron exhaust? If so the risers may be getting plugged. Thermostats are rarely an issue, these system are extremely simple people get caught up in making them more problematic than they are. Start at he beginning there is a very simple pump test right out of the tech manual, remove the outlet hose from the pump route it to a buck. Start the engine let it run 30 seconds you should have about 1-1/2 gallons in the bucket, don't worry you will not burn your hoses in 30 seconds. Also diagnosing air in the system is very easy, replace one riser hose with clear plastic. You may need a long section if you have a deep engine bay, go for a short run if you have air ingestion you will see the stream of bubbles in the line. I keep an 8 foot piece handy which also has a pressure gauge T'ed in, that allows me to check for air and also system pressure. Above norm pressure indicates plugged risers, low pressure with a known good pump puts the problem before the pump.

One thing to check... You might be low on water PSI into the engine. You might have enough flow NOT to throw a low water PSI code but it might not be enough to efficient cool the engine.

One thing we notice all the time is the water passage through the transom gets blocked off with the calcium build up from the water and can close the passage.

I would suggest to remove the water inlet on the inside of the transom (plastic water neck that your 1.25" hose connects too. Angles to the Starboard side). Sometimes they almost completely plug themselves off.

If you do notice there to be a major blockage (AKA a pencil will not fit through the hole), remove the drive and water hose on the outside and try to fill with CLR or any other super strength cleaner and a wire brush of sort.

If the sea pump housing has some wear, just replace it to eliminate any thought of a problem. The impeller is meant to be sealed on both sides to ensure that there is the proper suction to pull the water. Any altered surface will restrict the efficiency of the pump and cause to loose the proper pressure.

Sorry I am not a writer and an just throwing out my thoughts. Please feel free to give us a call, we are here to help you out and answer any questions you have to resolve the issue. -Eric

Last four posters, read a little. The original poster remedied the problem in August. Hint , last post prior to yours:lolhit::party-smiley-004: