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1998 5.7 L overheating at higher rpm's

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mikem40

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Raw water cooled salt water use new impellar in the spring. always ran cool but today it started to overheat. Cooled down restarted w/ same result. It had good water flow in the T-stat housing, the belt is tight, the circulating pump seems good ( no leaks or woobles) It will idle at 175 & stay there but at 3000 rpm's the temp shoots up. The risers & manifolds are original. I am going to check the PS cooler & the exhast flaps, hoses & T-stat but if I do need new risers & manifold where is the best place to buy them? Any brands too avoid
All suggestion welcome. TIA
 
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Re: 1998 5.7 overheating at higher rpm's

check the t-stat first ,check risers second and flapper maybe your lucky and the t-stat is half stuck closed.
 
Re: 1998 5.7 overheating at higher rpm's

12 years in salt water, it's time for new manifolds and risers. GLM is not a reliable Chinese product.
 
Re: 1998 5.7 overheating at higher rpm's

mikem40 said:
Raw water cooled salt water use new impellar in the spring. always ran cool but today it started to overheat. Cooled down restarted w/ same result. It had good water flow in the T-stat housing, the belt is tight, the circulating pump seems good ( no leaks or woobles) It will idle at 175 & stay there but at 3000 rpm's the temp shoots up. The risers & manifolds are original. I am going to check the PS cooler & the exhast flaps, hoses & T-stat but if I do need new risers & manifold where is the best place to buy them? Any brands too avoid
All suggestion welcome. TIA
Click to expand...


could be a head gasket
 
Re: 1998 5.7 overheating at higher rpm's

Just ordered risers, manifolds and spacers from I-net marine:

http://inetmarine.com/

Lowest prices I could find, OEM parts, and even though I paid for UPS ground, most of the stuff was on my doorstep the next day. The rest was there within 2 days.
 
Re: 1998 5.7 overheating at higher rpm's

Changed the t-stat last night & went for a quick run. I was running about 4000 rpm & the temp was 170. The old t-stat was rusty maybe it wasn't opening all the way. All the hoses were good. The risers were hot but not so hot you couldn't keep your hand there( like the other day). I hope thats it. I guess I'll know for sure the next time I go out again. Thanks for all the assistance.
 
Re: 1998 5.7 overheating at higher rpm's

170 is perfect. Whatever you did you did good cause maybe i don't understand the ordering stuff you posted.
 
Re: 1998 5.7 overheating at higher rpm's

chiefalen I only picked up the t-stat & installed it. The old stat was rusted pretty bad , I don't think it was opening properly
Another poster ordered the manifold kits
Thanks again
 
Re: 1998 5.7 overheating at higher rpm's

Went out for a run today. The temp was good for the first 1/2 hour then I overheated again. Let cool for 1/2 hour started & returned to dock (170) the whole way back @ 3000 rpm. I check the exhaust flappers One was gone the other ok. I couldn't find any pieces in the Y tube. The water pump was changed in the spring & the T-sat the other night. I guess I'll have to pull the risers & maniflods. Any other ideas??
 
Re: 1998 5.7 overheating at higher rpm's

just pull the risers first. Then after you look at them and the flappers we will talk about the mani's
 
Re: 1998 5.7 overheating at higher rpm's

Haven't pulled the risers yet. But I found a Merc service bulletin about overheating at over 3000 RPM's. I ran a clear hose from t-stat to the starboard manifold & went for a ride all was well until about 3500 RPM's & then suddenly no water. This happened twice. The merc fix is to use perfect seal on the first gasket against the housing. The impeller was changed in the spring & I never used perfect seal B4. So I'll try that & post back. Also my port shutter was almost completley gone so maybe I'll find part of that in the drive also.
 
Re: 1998 5.7 overheating at higher rpm's

Pulled the drive today & found my exhast shutters in the exhast by the shift shaft. I also found oil in the main bellows & leaking from the drive shaft.
Whats the best wwayto get those drive shaft oil seals out? This upper was supposly resealed in the spring along with the gimbal & bellows kit. Is it possible for the overheat to cause the leaks? At least i pulled the drive B4 I had alot of damage.
The water pump looked good but changed it anyway while it open.
 

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Re: 1998 5.7 overheating at higher rpm's

You solved the flapper issue me i would leave them off. When you run the boat when you come to a stop leave the boat idle for 3-4 minutes before you shut them off for alot of different reasons one being and wake that hits you in the back won't be able to travel up the exhaust tube when the motor is running.

And if you don't beach or boat then you don;t need no stikin flappers.

Ok the seal problem is related to the guy who did the work he missed something.

So if you want pressure test the drive now that its off and see if the oil comes out the shaft seal.

Me i would be royally pissed cause no way the motor overheating caused the seal to go.
 
Re: 1998 5.7 overheating at higher rpm's

mikem40 said:
Went out for a run today. The temp was good for the first 1/2 hour then I overheated again. Let cool for 1/2 hour started & returned to dock (170) the whole way back @ 3000 rpm. I check the exhaust flappers One was gone the other ok. I couldn't find any pieces in the Y tube. The water pump was changed in the spring & the T-sat the other night. I guess I'll have to pull the risers & maniflods. Any other ideas??
Click to expand...

Twice I have found the shutters had broken off. They get stuck down in the outdrive exhaust port right at the vertical shifting linkage.
 
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