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70HP Cooling system

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rude70

Contributing Member
"I have just fired up my '

"I have just fired up my '77 70HP after a complete rebuild. It fired second crank and idled great. I have the engine in a tank of water filled to around the top of the water pump (new impeller fitted). Water came out of the tell tale (tapped into the exhaust manifold) initialy then stopped after a few minutes. Plenty of water comes out of the two holes in the leg below the exhaust adapter. I ran the engine fo approx 20 mins at a fast idle. The temp of the water coming from the holes in the leg was approx 120 degrees. The head was warm/hot and the crank case on No.1 piston was hot - you could hold your finger on it for 5 seconds before it was too hot!. The bottom centre stat cover bolt has a leak (will silicone it tomorrow) with a fine jet of water, could this cause the lack of tell tale water? When I stop & restart initially there is a weak flow of water from the tell tale, then it stops. How long does it take for the engine to get to operating temp? The cylinder head cover was warmish, since I guess the stat had not opened! Have not taken it on the water yet since I want the cooling to be right. I am sure that it has not over heated since the head and cylinder case are not hot enough to touch. Any help is appreciated."
 
"I checked the hose & fitt

"I checked the hose & fittings, all ok. I could blow on the pipe so it is not blocked. The compressions are good 140/136/136. I ran it again today water came out of the tell tale but stopped after about 5 minutes. I put my finger over the outlet, let the pressure build and it ran again for a minute or so. The block or head was not hot after 5 mins of running. Perhaps the stat has openned! I plan to run the engine on the trailer in the sea at half throttle. Any advice why the tell tale is stopping??

Thanks"
 
"I tried it on the muffs conec

"I tried it on the muffs conected to the hose. The tell tale stream was strong and virtually no water came out of the holes in the back of the leg below the exhaust adapter -perfect! There was quite a lot of water coming out I uess from the leg where the gear shift comes through. Put it into the bay on the back of the trailer in gear at 2000rpm and tell tale stream was weak again. I have replaced the impeller when rebuilding, could it be something to do with the seal around the drive shaft? Thanks"
 
Do You have the thermostat ins

Do You have the thermostat installed?
Sure it is working and not leaking?
Double checked the relief valve with correct spring tension?
 
"I installed a band new thrmos

"I installed a band new thrmostat - i tested it before intalling. Also installed new gaskets with full engine rebuild. I re-used the relief valves & springs - it previoulsy pumped fine. Iguess the next step is to remove the lower unit and check that the pump housing is sealing to the plate ok. Manual says to use 1000 sealer, which I did not do! Any thoughts? thanks"
 
"When You changed the impeller

"When You changed the impeller, how was the condition of the big rubber gasket between exhaust tube and lower gearcase?
If that is not perfect or have been dislocated during assembly, exhaust will enter water pump and reduce capacity."
 
"I did not look at that gasket

"I did not look at that gasket, I will take the leg off and investigate, thanks"
 
"I have replaced the exhaust g

"I have replaced the exhaust gasket, the impeller housing o ring seal and the wear plate gasket (between wear plate & gearbox. The tell tale still reduces to a drip when in a tank of water. I ran the engine in the tank for 15 minutes between 1000 & 2000 rpm (using fast idle) but the head does not get hot at all. The OMC temp gauge is on the upper part of the blue - I poored boilin water on the send and the gauge moved to over half - so it works! Even on the muffs, the engine does not get hot, probably around 120 degrees. I am now thinking that water is leaking past the stat (a new sierra tem) or relief springs. Any ideas?"
 
"u should still have a pee str

"u should still have a pee stream,even if wtr leaking past therm...ck the line,and FITTING,on block....it does'nt take much to block it...r u sure u got the rubber seal,in the tube,on wtr pump hsng,where eng wtr tube slides in to...?"
 
"have u tried it,in the lake?.

"have u tried it,in the lake?..make sure muffs are tight,squeeze together,tight a seal on LU as poss.....full wtr pressure."
 
"actually,this one,did not hav

"actually,this one,did not have what we call a 'pee stream'...i dont thgink,maybe someone added one....do u have a hose leading to lower pan,or,are u referring to the back exhaust relief area's?"
 
"Yep I backed the trailer in b

"Yep I backed the trailer in before installing the new seals. When I ran it in the tank the water level was about two inches above the cavitation plate. The muffs were tight, I also squeezed them but no difference. The motor aint getting hot! I have noticed quite a bit of water coming out of the gap whci is the notch in the tunk where it meets the lower unit. Is this normal? But if it was lack of water pressure wouldn't the head get hot real quick?"
 
"Hey JWB, soory our posts cros

"Hey JWB, soory our posts crossed. The tapping for the 'pee-stream' is into the exhaust manifold 2" from the top. When the stream reduces to a dribble, if I hold my finger over it, pressure builds and the flow continues for a while, then stops!"
 
"sure sounds like a pump probl

"sure sounds like a pump problem,..sounds like it is weak,..or sucking air/low volume,low pressure...i'd go back to pump.,make sure the rubber seal,is in pl for the wtr tube...u may have a prob,where the wtr tube,conns to adapter plate,under pwrhd."
 
"Thanks, I used another trunk

"Thanks, I used another trunk since bolts broke off on the original trunk. May be I should have the boles removed and go back to the orig trunk!
But why would the motor not heat up?
I have added pic of lower unit on muffs showing water stream from fron of unit. I think it is also present in the tank, not so strong. How does this occur?
Thanks
283840.jpg
LU water stream
 
"it is fairly normal,to have t

"it is fairly normal,to have that occur,but ,not,..in a high volume,scenario...once again,makes me think of a pump,or grommet prob...eng not overheating,is a good sign,...but,it WILL if u have no,or low,wtr volume,in the pwrhd.,esp,..under load.
r u sure,u got that grommet,seal,in where the wtr tube goes,..it would pay to dbl ck it,..i have had them,crush,and bend over,close off flow,etc,..but,90 of the time,no prob....thats where i'd go...ur wtr SHOULD be,discharge,is it warm,or cold...hose temp?"
 
"Thanks, I offered the pump ho

"Thanks, I offered the pump housing up to the water tube before assembly & from the underside of the pump housing I could see the metal water tube - the grommet was in place.
I will remove the LU, attached a hose to the water tube to see if there are any leaks under the powerhead. I will also check grommet again. Will also check the discharge temp, from the two holes in rear of trunk under the exhaust plate adapter, the water was warm, about 120 degrees. Thanks for your advice"
 
"u can also,run that eng,but i

"u can also,run that eng,but it will idle,very fast,w/no load fr lower unit on it.....if u now get a good stream,something..is...amiss..in the lower unit..wtr pump system.put that hose on wtr tube,and hose clamp it....u r on,the right track."
 
"Hey JWB, I finally fixed it -

"Hey JWB, I finally fixed it - the water pump. I had a spare gearbox with water pump intact. The impeeler looked in excellent nick, so I bolted her up hooked the leg up and pee stream stong and engine warming up nicely. The only difference I could see between this old pump and mine was my impeller was new and rubber a lot harder, and my wear plate had half the size cut out to suck the water and no small hole. So I put the complete assembly on my gearbox and all runs well. Thanks for your help, Rich"
 
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