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Overheating at low rpms

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onnfire

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i hope someone can help. I ha

i hope someone can help. I have a 99 volvo penta 4.3 gi I was overheating when i first started my boat the begining of the season. My impellar and thermostat was shot. I replaced them now I am overheating again but at low rpms. and tonight what really got me is that it is overheating no matter what. my impellar is fine. could my thermostat be shot again?
 
"Check the thermostat housing,

"Check the thermostat housing, the exhaust manifolds and the risers. Also, have you checked the condition of the raw water pump impeller? And if you changed the impeller lately, were chunks from the old one missing?"
 
I checked the impellar which i

I checked the impellar which is fine. the old impellar did have some pieces missing. I ran fresh water through after opening most of the drains and had debris come out but no luck. The thermostat housing was pretty clean when I opened it 5 weeks ago to replace the thermostat. I will try the exhaust manifolds and risers tomorrow. Would it be worth replacing the thermostat again since it was overheating?
 
"If your thermostat is fine, r

"If your thermostat is fine, replacing it won't help. I would just test it in hot water (you only need a stove, a pot with water, and a thermometer), and if it opens at the specified temperature, then your problem is elsewhere.

Also, check the outlets in the thermostat housing, you may find an old piece of impeller stuck in one of them and causing the symptoms you describe.

Have you cleaned the intake grid in the outdrive and verify it is not obstructed? If you keep the boat in salt water all year round, check for barnacles growing inside the outdrive suction space."
 
One quick question about the t

One quick question about the thermostat. Could I have positioned it wrong? I found an article in my shop manual that I need to make sure the element is facing me. I never did make sure. Could this be my problem. If it is I am still going tlo do all the work you recommended since it can't hurt. Also thank you so much for all your help. I am gratefully appreciative of your help and knowledge.
 
I know I installed it that way

I know I installed it that way. I Thought maybe the thermostat had to be in a certain position. Guess not. I was hoping. I need to order the gaskets for the manifolds and risers and I will tackle them. I looked in my manual to see about the grids and couldn't find them. I have never taken apart a lower unit yet but I will attempt this tomorrow. Thanks again.
 
"-----------------------------

"--------------------------------------------------------------------------------
You don't need to take the unit apart. The grids are at the left side of screw 4, just make sure they are clear. You should be able to see through them . You can also"
 
"I have had a problem with low

"I have had a problem with low water flow and the impeller looked "fine" as well. They get worn in one direction and don't develop as much pressure to move water. Sometimes you can flip them around so that the the impeller is moving opposite the "worn" direction. I'd just get a new one, they're cheap and simple to replace. Get two, always good to have a spare.

K"
 
Okay so I replaced my impellar

Okay so I replaced my impellar again and started it up and water was coming out of the exhaust within 30 seconds of startup and ran like a champ for 15 minutes at low rpms and not having to raise them. thought i was in the clear so i went in the river and it overheatd again and it would cool down when i raised the rpms. so i opened up the housing when i got home and one of the fins were turned the wrong way. so it looks like i overlooked putting the impeller in correctly. could that have caused overheating again and do i need to replace it again?
 
"When you shut the engine off,

"When you shut the engine off, the engine can spin backwards when it stops because of compression. This can flip a few of the impeller fins backwards. Just a thought for you to bare in mind."
 
Thanks I am waiting for the ga

Thanks I am waiting for the gaskets for the risers and manifold to come in. It seems like a lot of work to take them apart but if that what it takes. I just dont understand why it worked for the first 15 minutes but then starts overheating again. But I guess thats why I am a plumber and not a mechanic. If I take off the plug on top of the circulating pump and startup the engine can I tell if it is working properly. Or do I need to take apart the pump and look inside if I can? Is there a brass impeller inside of that? I might just get some new gaskets for the circulating pump also...
 
"So tonight I took off the por

"So tonight I took off the port side riser and exhaust manifold and there is some obstruction but not completely obstructed as far in as I can see. How is the best way to clean them. I heard boiling them but I can give them an acid bath, would that be better? Once I figure this out I will take apart the starboard side. But I have heard they tend to go bad within a year of cleaning them. Has anyone had a problem with that?"
 
"After acid dipping, parts of

"After acid dipping, parts of the riser and manifold will become very thin in places. (especially where you cant see) These can crack or "blow out" often leaving you stranded. If you can, go for new."
 
this is sounding like a thermo

this is sounding like a thermostat problem. take it out completely and try running the boat and see what happens. don't take the manifolds off to replace those gaskets. i doubt that is the issue and it's a pain.

keith
 
"Well I replaced the thermosta

"Well I replaced the thermostat several weeks ago. I took Els advice and I already took them off. Both manifolds and riser slots were full of scale and debris and inside also. I cleared them through with the hose and got 99% of the debris out. So I am going to put them back on tomorrow and make sure that was it. I also bought a used circularting pump in great condition with very low hours just in case. A friend was telling me that if I hear squealling at times and the belts are tight that usually it means the pump is going. Back to the manifolds and risers, some of the dividers are deterioting and either way this winters project is going to be replacing them. And if its not I will try the t stat again. Thanks for the advice I just got to it earlier this week and havent finished up. Hopefully it works. I will update tomorrow night if all goes well."
 
"Well I put the risers and man

"Well I put the risers and manifolds back on. To my luck (which at this point is slim to none) it was overheating. I did notice though that my impeller housing is getting real hot before it reaches temperature, to the point where I burned my fingers pretty good. Is that normal? I am hopefully today, if not tomorrow then, going to get a new thermostat and gaskets for the circulating pump and change the pump also. One other question, the brass plating on the bearing housing that is connected to the impeller housing is scored and has ridges. I was told i can slightly sand it down to smooth it out. Can that have a factor in not getiing enough water. And shouldn't I have water flow within the first 30 seconds out of the exhaust when I first start up the engine?"
 
"David,
if the brass plate th

"David,
if the brass plate that covers the impeller has ridges or scores the impeller will lose its ability to pull water well. (the impeller needs to be a very snug fit inside the housing). Make sure the plate is completely flat and smooth. Unless the engine has been winterised you should have water coming from the exhaust within 10 seconds of starting. The impeller housing should never get hot during operation, to me this confirms that at low rpms the impeller is not pulling water and the rubber is heating up the case due to the lack of water. It seems your main culprit is the raw water pump. I would focus on this for the time being."
 
"Though not impossible, that w

"Though not impossible, that would be really difficult to do, as suction and discharge hoses would look crossed. The suction side is the lower port in the pump on the link.

http://www.volvopentastore.com/WATER_PUMP/dm/cart_id.497973580--category_id.3423 92--session_id.493100379--store_id.366--view_id.312615

David, if the pump is getting hot it is simply because it is not sucking/pumping water. And if it is not sucking or pumping water is because either the pump is toasted, or there is an obstruction on the discharge side, or because there is either an obstruction or an air ingress source on the suction side.

I think you have pretty much isolated the problem. Not many places left where too look for the problem. Now, one question: is the cam inside the pump housing (5 on the above link) in good condition? And most important: if the cam is removable, is it in place or was it accidentally left out?"
 
"There is nothing inside of th

"There is nothing inside of the housing except for the impeller. I took a fine piece of sand paper and sanded down the bearing housing and the inside of the impeller housing to smooth it of all scratches. When I reinstalled it I started the engine and worked great. I stopped it to replace the sealing ring due to it passing water and leaking. When I restarted it, the engine overheated again. It seems as though when I get it to cool down I can restart it as long as I dont shut the water or thake the muffs off. But if I do then it overheats again as though the water that drains from the outdrive is gone it won't suck it back up until I raise the rpms. I think you are right El I do need a new housing but also a new bearing also. One more thing. I do hear squealing at times. Is that a sign of a bad circulating pump? The belts are tight and not getting wet when I here it."
 
"Could you upload a picture of

"Could you upload a picture of the inside of the pump housing? I would like to see if there is a cam or not.

Also, if you take the whole pump apart, you will find out if the bearing is rough or not by just turning it. If you are going to overhaul the pump, I suggest that you replace the bearing, the seal and the impeller"
 
Thanks El. Sorry for the dela

Thanks El. Sorry for the delay. I am going to get those photos tomorrow. My boat is at my fathers house with a better facility to work. So hopefully I can get them downloaded and sent to you.
 
"El Pescador,

I am

"El Pescador,

I am sorry for not getting back to you. I decided to just buy a new raw water pump. In doing so I found out that the bearing housing is not supposed to come off the shaft that it is pressed on. Well when I originally took it off the bearing housing came off also and not knowing any better I assumed it was fine. Long story short I insalled a new one and it runs like a champ. I guess since the housing was able to come off and the thrust plate and housing was scored like it was that it really needed raplacing after all. I just wanted to say thank you very much for your constant help and for everyone elses imput. I wish I could return the favor back to you somehow. Thank you again for your expertise, help and wisdom."
 
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