454 overheating

There is another factor at play here. . . .engines need to shed more heat when at high RPM. Engine driven pumps spin faster at high RPM.

A working system will have "margin" between cooling capability and engine load at all rpms. As a practical matter, the system has much more margin at idle RPM than it does at cruise RPM.

That is a good thing. It is easier to dock at idle RPM than cruise RPM. . . .
 
Have a buddy of mine who still has a problem with his engine (a single screw5.7 IO) that still runs hot once in a while while trolling. He bumps his RPMs and the engine drops temp to what it should be. He watches and when it starts again he repeats this process. He has replaced the impeller at least twice and still the same result. I am following this thread to see what else I can learn for him. I am not a mechanic, but do a lot of my own repairs as I'm from the "old School" and do what I'm capabl, of but leave the rest to qualified people. It's going to be interesting to see what else comes up in this thread as I would really like to help him here.
 
tollycraft said:
Have a buddy of mine who still has a problem with his engine (a single screw5.7 IO) that still runs hot once in a while while trolling. He bumps his RPMs and the engine drops temp to what it should be. He watches and when it starts again he repeats this process. He has replaced the impeller at least twice and still the same result. I am following this thread to see what else I can learn for him. I am not a mechanic, but do a lot of my own repairs as I'm from the "old School" and do what I'm capabl, of but leave the rest to qualified people. It's going to be interesting to see what else comes up in this thread as I would really like to help him here.
Click to expand...

Risers and manifolds, power steering cooler, impeller, thermostat, engine water pump, or hose restriction. It can't be much more than that.

Doug
 
sfergson727 said:
Replace the impeller.

Gary, Gary, Gary......you big boat guys are really out of touch. A 268 dancer is an IO boat, with the water intakes on the lower unit. Ram pressure can and does affect the amount of water intake.
Click to expand...

I'd still beg to differ. There is no 'ram effect' because the flow of water is still across the water intake on the lower leg. There is no scoop for the 'ram effect' to take place.

Doug
 
sfergson727 said:
Gary, Gary, Gary......you big boat guys are really out of touch. A 268 dancer is an IO boat, with the water intakes on the lower unit. Ram pressure can and does affect the amount of water intake.
Click to expand...

I think I qualified my response by saying I didn't know what drive set up the OP had. If it's an i/o with a forward facing intake, I agree. But I *know* Greggy poo doesn't have an i/o and that's what I was talking about. However, these are displacement pumps and you can't "blow by" them unless most of the fins are missing on the impeller.
 
douglee25 said:
I'd still beg to differ. There is no 'ram effect' because the flow of water is still across the water intake on the lower leg. There is no scoop for the 'ram effect' to take place.

Doug
Click to expand...

Shows what I know about i/o drives... If the drive is like the lower unit on my 135HP Honda, then it's not going to pick up water the faster you go... like Doug said.
 
You are right... I've never owned an i/o... just outboards, jet drives (3), and, God forbid, boats that had SAILS on them....
 
Sometimes technical people (mechanics, IT people, maybe even a dentist or two) will propose a quick oversimplified explanation for something that they dont feel much like taking the time to explain properly. Other times they just make stuff up. Fact is, with perfect impellers and a perfect cooling system, a temp spike is to be expected after a rapid throttle down b/c the manifolds and risers are at their hottest. Suddenly, you have decreased their cooling water flow and you get a transitory increase in temp followed by a decrease. Try this. After a run and before you shut your engine down, feel the risers. If they are functioning properly, you should be able to touch either without scalding. Now shut the engine and wait 5 minutes. Touch now - you might get burned. The heat source is still there and building up like an big old cast iron radiator. But the cooling source is cut off. I cant judge the competence of your mechanic but his explanation is off base.
 
Last edited:
rondds said:
Sometimes technical people (mechanics, IT people, maybe even a dentist or two) will propose a quick oversimplified explanation for something that they dont feel much like taking the time to explain properly. Other times they just make stuff up. .......
Click to expand...

So....while I was diving and hit the sand at 110' two weeks ago, I get this sharp pain in my top moler....air pocket under the filling?
 
PRECISELY! Actually, at that depth, there's a pressure differential btwn the atmosphere and the internal "hollow" of your tooth where the nerve resides. This pressure differential compresses the nerve, either in the tooth or in the surrounding periodontium. Because these nerves are purely nociceptive, all you feel is PAIN. This is why, during WWII, the Army Air Corps and Navy pulled every tooth with a questionable prognosis. That is also why i do NOT recommend starting a root canal that cant be finished before a trip involving air travel.

NOW, isnt "there's an air pocket in your tooth" much simpler?. Most people dont give a crap about the techno mumbo jumbo. "Just fix it Doc!"
 
:wow: Admin cuts yer balls off and ya get all scientific around here...:smt021
 
:grin:
 
Exactly... By the way my 1984 Tomos moped is running a little hot. Is it because i have lost a little off the top end and the air flow is less or is it the because I haven't replaced my spark plug since 86'
 
Oh i din't see that Stu was actuallly Wayne. Maybe his engine is running hot because he boats in Stew?
 
Zorba said:
Exactly... By the way my 1984 Tomos moped is running a little hot. Is it because i have lost a little off the top end and the air flow is less or is it the because I haven't replaced my spark plug since 86'
Click to expand...

Probably because you've gained weight and the moped is working harder.
 
fat_guy_moped1.jpg
 
For some reason the auto notification was off so boy was I surprised to check this thread and find 40 responses. And boy have you guys been having fun :) First I can see I need to give a bunch more info and answer some questions

I have Alpha I OD
Single engine
This usually happens at idle or when cruising at under 7 knots and it does not always happen. I just got back from two weeks on the water and it only happened a couple times.

The engine was completed overhauled with all new parts just 18 months ago and has less than 50 hours on the rebuilt engine. The impeller was replaced at that time for sure since the mechanic happened to do it right in front of me
I don't have a raw water pick up scoop so that is why I have the impeller I believe.
The service manual says that the magnum 454 has a stern drive pickup pump
When I look that up, it appears to me to just be the impeller. Sorry I am not a mechanic.
The boat is on a trailer and I dip in the ocean at least once a month for a whole weekend

Hope that helps give a few more clues.
 
You must log in or register to reply here.

Forum statistics

Threads
113,253
Messages
1,429,340
Members
61,130
Latest member
VaBreeze
Back
Top