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Mercruiser overheating

J

josh0807

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i have a 1979 mercruiser 898 i

i have a 1979 mercruiser 898 i have done everything i know to do and still cant get it right i have replaced 1 of the log style maifolds and rodded the other out i have replaced t stat and cleaned housing i have replaced circ pump on engine i checked for kinks and clogs from raw pump hose through transom i droped foot and hooked a garden hose to every hose and blew water back through foot and found nothing i replaced the impeller in the foot. Today i cranked engine on muffs and disconnected the hose that pumps raw water from the foot at t stat housing and put in a 5 gallon bucket in 1 minute i got 2 and 1/2 gallons at 500 rpm is it possible that i got it to tight an the impeller is not working properly also were this hose connects to the t stat housing when i took it off it seemd as if it was blowing back harder than the pump could push it seemd that it was over powering it backwards.thanks josh
 
Have you checked temps with a

Have you checked temps with a temp gun?
Gauges can lie.
Give us more info regarding how it is overheating and wheree. Are the manifolds and risers hot? What temps?
what T'stat?

Rod
 
"500 rpm is a tad slow, should

"500 rpm is a tad slow, should be 650 or so.
Could be lack of flow due to low rpm. When trolling I often turn idle down to 500 for speed control and my temp will slowly creep upwards of 200, then I throttle up to 650 and she cools right back to 160. I have all new cooling components and hoses. I traced it to impeller flow at this rpm. Note, mine is a gen 2 and they flow more water by design than gen 1 and my thinking is they may be more inclined to produce this problem at lower idle speeds.
2_cents.gif


Kurt"
 
"hey rod sorry it took me so l

"hey rod sorry it took me so long to get back to you. I have not checked with a temp gun but the manifolds get so hot that i cant keep my hand on it for more than 5 seconds risers are not quit as hot.I had a 165 t stat and took it out just to see if that would help and it didnt.Also all hoses are very hot both hoses that go from t stat housing to riser,both hoses that run from manifolds to t stat housing and hose that runs from t stat housing to circ pump. The only hose that is cool is the one from the raw water pump to t stat housing.When out at the lake last it would run cool as long as i was running across the water no matter how fast but as soon as i put it in neutral it would start to overheat put it in gear and start moving it would cool back down.
Thanks for all your help
Josh"
 
"I was reading about the type

"I was reading about the type of T'stat hsg. w/o diverter balls. There is a "by-pass hole" inside the housing. If it is narrowed it causes water hoses to expand when the thermostat is closed because the water can't get out fast enough.

If the hole (1/2" +/- 1/32") is over size, it can cause the engine to overheat at idle or low RPM because too much water is flowing out of the by-pass.

Early models have an inspection plug on the bottom of the hsg. If there isn't a plug, it must be drilled, 23/32" or 18.5 mm, and tapped for a plug, 1/2-14 NPT or M20X1.5 and A20 sealing washer. The hole needs to be drilled in a specific location from the bottom."
 
Guy i checked the by-pass hole

Guy i checked the by-pass hole in the t stat housing and the rest of the housing every thing looks to be free and clear i can see through the by pass hole I had a 1/32 drill bit and stuck it through the hole i could slide it back and fourth freely.Any other suggestions.
Thanks for your help
Josh
 
You may have a problem w/the w

You may have a problem w/the water pocket in the OD where the copper tube fits into the base of the upper half. You stated "it seems to be blowing back harder than the pump can push it". That could be a symptom of a water pocket seal problem. Do a search above on "water pocket" w/in the last 10 days under mercruiser for pictures of a damaged one.
 
Guy
no the hole was not enlar

Guy
no the hole was not enlarged at all it actually looked pretty good.I read the whole thread of rich's overheating problem and seen his toasted water pocket so i know what to look for i was kinda thinking that may be my problem but i was not sure so i will drop the lower unit and check that.I appreciate all your help and i will let you know what i find
Thanks again Josh
 
Guy
I droped the lower unit

Guy
I droped the lower unit and pulled the water pocket it looks pretty cooked it has little bubbles all over it looks like it has been hot im going to order a new water pocket im sure this happend when i found the shredded impeller do u think that is what caused the water pocket to get hot or do i need to check something else.
Thanks a millon Josh
 
Guy thanks
Im going to order

Guy thanks
Im going to order a new water pocket and i will let you know how it goes when i get everything back together
thanks again
Josh
 
Guy
I got the new water pock

Guy
I got the new water pocket installed this weekend hooked the muffs to it and cranked it i let it run for over an hour on the muffs the temp never got over 150 with no t state the manifolds risers and hoses are still hot to the touch i could rev it up to about 1000rpm and it would drop down to 140.Is this normal for man. risers and hoses to be this hot.Also i could drop a drop of water on intake and it would sizzle.Thanks for all your help
josh
 
Put the 143 deg. T'stat in

Put the 143 deg. T'stat in it. The mans. and risers should not be so hot. You should be able to lay your hand on them w/o feeling a hot sensation. Is the garden hose on full pressure?

Your idle RPM should be 650-700 RPMs. For the heat problem your engine is having it just seems that there is insufficient cooling water flow thru the mans. and risers. Get a laser thermal temp gun and find out where the hot spots are occuring.

Have the risers been checked and cleaned? Small passages can get plugged w/rust buildup and decrease exit flow of cooling water.
 
the only exhaust part that is

the only exhaust part that is new is the starboard sid man.I tried to clean the rest myself prob. did not do good enough do you think a radiator shop could clean these parts other. man. and riser?thanks josh
 
Thanks guy
I think i will ge

Thanks guy
I think i will get a temp gun and try to pin point the hot spots befor i break all that down.I will try to do that this weekend and i will let you know what i find.
Thanks again for all your help
 
Ok i got a ir temp gun and got

Ok i got a ir temp gun and got some numbers and thay are starboard riser 165 starboard manifold (new one)170 port riser 187 port manifold 190 top of t stat 171 circ pump hose 137 water inlet hose 97 all hoses 165-168and the crazy one is the intake manifold and it ran from 212to400 hope this will help us out.thanks
josh
 
"crazy one is the intake m

"crazy one is the intake manifold and it ran from 212 to 400"

My thought is those numbers are too high. When was the last time the intake was off the engine?
 
"Josh
If you have not already

"Josh
If you have not already looked at it, you should read the entire topic called "1990 5.7 water presure?" just down the list.
It deals with a case of an Alpha pump sucking air along with the water, and I am thinking your problem may be related, if not identical.
It would sure explain the weird temperatures.

Check it out.
Rod"
 
I believe you install a clear

I believe you install a clear segment of water intake hose and look for air bubbles. It can be purchased with reinforcement built into it.
 
"Ok i put a clear hose on the

"Ok i put a clear hose on the cooling system and at idle everything looks good run it up to 15 to 2000 rpm and it has a lot of air bubbles running through the clear hose.Is this what i dont want?How do i fix this.Also i checked the intake again it showed 312-400 middle runner what would cause that to run so hot.Also checked middle port om exhaust manifold it was about 200 is it normal for exhaust to run that hot,
Thanks josh"
 
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