only overheats at full throttle ???

[riskibusiness]

!980 wellcraft with a 470 170 hp. I can run on muffs in driveway all day or troll around the no wake area for hours with no problem but as soon as I go full throttle it starts to overheat W.T.F.

 

[dubs283]

Re: only overheats at full throttle ???

when was the water pump and base assy in the drive last replaced??

 

[stonyloam]

Re: only overheats at full throttle ???

Three cooling water possibilities here: 1: as dubs suggested impeller, 2: heat exchanger passages blocked (pull the end covers to check) 3: the raw water passage in the exhaust elbow is restricting the raw water flow. If your thermostat is not opening fully it could cause a problem like that. The impeller is the far more likely culprit.

 

[riskibusiness]

Re: only overheats at full throttle ???

has a brand new impeller but the old on did come apart due to muffs falling off in the driveway. so I might have to pull the exchanger and check it for blockage. I dont know the age of the engine coolant pump.

 

[stonyloam]

Re: only overheats at full throttle ???

Don't have to pull the exchanger. Pull the front cap. The inlet is the top front hose if there are impeller pieces that are large enough to block the tubes they should be there. Don't worry about the antifreeze, it is inside the exchanger body, it will not leak out when you pull the cap. If it is dirty in there you might want to pull the rear cap too and flush out the tubes. Any pieces small enough to pass through the tubes should have been flushed out of the system. If your engine water pump is not leaking it should be OK, there is essentially nothing to ware out there since the aluminum impeller is bolted directly to the cam. In other words no pump bearings, just the two seals. Good luck.

 

[riskibusiness]

Re: only overheats at full throttle ???

any chance a head gasket could cause this problem?

 

[matthysone]

Re: only overheats at full throttle ???

If you haven't already, upgrade to a 4" heat exchanger. I had same problem with my 3" exchanger.

 

[stonyloam]

Re: only overheats at full throttle ???

any chance a head gasket could cause this problem?

I would not think so. With a blown HG you would have very rough idle, or air in the coolant. If it is running well that is probably not the problem. Borrow the tools from Autozone to do a cooling system pressure check and a compression check and find out for sure.

 

[riskibusiness]

Re: only overheats at full throttle ???

O.K. guys I checked the exchanger (clear) checked flow at the elbow(good) ran it on muffs in the driveway for about 45 min (stayed around 115 degrees) I even reved it to 200 rpm a couple of times and no change. You can even touch the exhaust manifold and elbow with your hand. They're hot but not to hot to touch. I guess I will take it out tomorrow and check it out???

 

[stonyloam]

Re: only overheats at full throttle ???

Sounds like the raw water side is OK. If it still overheats at full throttle, you might want to check out the thermostat to make sure it is opening fully.

 

[fmalott]

Re: only overheats at full throttle ???

Sounds like the raw water side is OK. If it still overheats at full throttle, you might want to check out the thermostat to make sure it is opening fully.

just following along here riski said on his #1 post it overheats at full throttle i hope on the lake, then on his #9 post it didn't over heat on the muffs
even at 200 rpm. how can one find out what the problem is if it only overheats at WOT you can't find that info out in the driveway i would not even attempt WOT on the muffs. so that being said it sounds like there still is a restriction on the water flow

 

[achris]

Re: only overheats at full throttle ???

Three cooling water possibilities here: 1: as dubs suggested impeller, 2: heat exchanger passages blocked (pull the end covers to check) 3: the raw water passage in the exhaust elbow is restricting the raw water flow. If your thermostat is not opening fully it could cause a problem like that. The impeller is the far more likely culprit.

4. Leaking water pocket cover gasket....

It fits with the symptoms and given everything else you've checked, I'd put money on this one, especially since you destroyed an impeller 'when the muffs fell off'.... That's a classic for overheating and melting that plastic cover.

Chris......

 

[dubs283]

Re: only overheats at full throttle ???

i asked in my fisrt post about the BASE ASSY, you MUST always replace the base assy and gasket when doing a water pump on an mc-1, r/mr, or alpha one drive

what happens is the aft side of the base gasket fails and at higher rpms, exhaust fumes get pulled into the base assy and water pump thus aerating the water going to the engine

 

[riskibusiness]

Re: only overheats at full throttle ???

Just to be sure I understand. When you say base assembly or water pocket cover. you guys are talking about the impeller cover right?

 

[dubs283]

Re: only overheats at full throttle ???

the base assy is below the impeller, it has a double seal the drivshaft goes through - once the stainless plate and gaskets are off, pry up the whole base assy - there is a gasket below this that fails causing your issue

the water pocket cover is in the upper housing, it is what the copper tube presses into and is held in place by four bolts

 

[stonyloam]

Re: only overheats at full throttle ???

#24 here: http://www.mercruiserparts.com/Show...&bnbr=110&bdesc=GEAR+HOUSING(DRIVESHAFT)+-+MR and #2 here: http://www.mercruiserparts.com/Show...br=80&bdesc=DRIVESHAFT+HOUSING+AND+DRIVESHAFT

 

[riskibusiness]

Re: only overheats at full throttle ???

I'm going to order a whole new impeller kit with a new impeller housing and this time I will pry the base up and change that gasket. I started to last time but it was really stuck there and I was afraid I would break it. As far as the water pocket that is the top of the lower unit everything I've read about those is to leave them alone unless you absolutely have to. (bolts break)

 

[markheck1]

Re: only overheats at full throttle ???

FWIW if you are going that far, and have never done it, you should probably change the base too, not just the gasket, they are pretty inexpensive....

 

[dubs283]

Re: only overheats at full throttle ???

this time I will pry the base up and change that gasket.

buy a new base assy too, it comes with the right o-ring and gasket

the base has seals in it that seal the driveshaft - as long as you are in there just do it

like i said before, ALWAYS replace the whole water pump AND base assy when servicing these items

 

[riskibusiness]

Re: only overheats at full throttle ???

yep I already ordered that kit