1992 150 johnson fast strike quickly overheats

[3car]

I bought this boat knowing the engine had issues. Previous owners description sounded like it was going into SLOW mode, but he told me the dealer used an infared heat gun and it wasnt getting hot.

So, I started it in a tank. It started easially and idled fairly smoothly. If i reved it up, it hesitates and pops through the exhaust some. The tell-tale is warm and strong. after 30 seconds or so, the overheat alarm came on and stayed on. The heads are hot to the touch. I disconnected the temp sensors in the heads and the sensor on the shifter, but they didnt effect how it idled or throttled up.

Compression is between 105-110 on all 6, hour meter shows 303.

 

[OBJ]

Re: 1992 150 johnson fast strike quickly overheats

First question....running in a tank....was the level of water well over the mating line between the lower unit and midsection?

Second question...do we know the last time the t-stats/pump impeller were chanaged out?

AND...nuther question....were both heads hot? You need to check up near the t-stats. Just a little flat place forward of the heads. One head can over heat while the other stays normal.

 

[3car]

Re: 1992 150 johnson fast strike quickly overheats

T-stats and impeller were recently changed, and the stats still look like new. The water level in the tank was almost up to the mounting bracket, and both heads seem hot.

 

[3car]

Re: 1992 150 johnson fast strike quickly overheats

I took the boat to a guy who helps me out from time to time, and he was kinda stumped. we pulled the thermostats, and he thought the springs may be incorrect because they were very firm. We cut the springs in half and reinstalled them, and the motor ran noticably cooler. You can now leave your hand on the heads where before it was very hot. The springs are red. Is anybody familliar with these motors? Help!!!

 

[tashasdaddy]

Re: 1992 150 johnson fast strike quickly overheats

i have found this little $10 item to be one of the best tools in my kit. it verifies if it is really running hot. "http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93983". shoot the top of the heads, is the tale tell stream good and strong? if so i would think stats

 

[HighTrim]

Re: 1992 150 johnson fast strike quickly overheats

30 seconds seems awfully quick to overheat like that....you say the tell tale had a strong steady stream?? If the water pump and impeller are brand new and in good working order, there are no restrictions in the water line and the t stats are brand new, the only other thing that I can think of would be the deflectors in the head. If it is overheating like that, you might also want to take a torque wrench to all your head bolts.

 

[3car]

Re: 1992 150 johnson fast strike quickly overheats

Right now my main emphesis is on the thermostats and springs, because cutting the springs in half SEEMED to make the cooling problem disappear.
The motor has a good idle but dosent rev up well, but i suspect carburation for that.

 

[3car]

Re: 1992 150 johnson fast strike quickly overheats

I'm still struggling with this a little bit.