Logo
FULL SITE MENU

Overheating

S

skubadave

New member
"Hi All,
My 1988 305 started

"Hi All,
My 1988 305 started overheating. I replaced the themosat- no change. Replaced the intake hose and impeller-also no change. When I rev the engine the temp gauge drops rapidly but then climbs when I return to idle. It looks like water is exiting the exhaust, but.... I need some advice on what to check next. Thanks

Dave"
 
It sounds to me like you have

It sounds to me like you have some kind of pump or flow issue but you said you already changed your impeller and intake hose.Maybe your circulating pump or your external water pick up is clogged.I'm sure someone else will have more insight
 
When was the last time you had

When was the last time you had the exhaust elbows off (check them for clogging)?
 
"Dave, a little more informati

"Dave, a little more information please. Where has your boat been used. Is it salt water or fresh. Is it river or lake. If it is a river, what river. A lot can go wrong with a pump. Not only can the impeller be bad (which you have now changed) but the plates that are on both sides of the impeller can be worn. This happens more frequently where there is sand and sediment in the water. If it is a salt water boat, I would turn to the manifolds, risers etc.

Chuck"
 
"I'm thinking elbows are d

"I'm thinking elbows are due for replacement.

You can check the pump's capacity by letting it pump into a bucket and time it w/ a stop watch. You can also insert a clear piece of hose, temporarily, to see if the water flowing thru it is solid or aerated (bubbles are bad for a cooling loop).

Another option is to "catch" the water coming out of the exhaust pipe, at the transom. It should match what the pump puts out. (If the pump delivers 3 gallons in 30 seconds, those 3 gallons should go out the exhaust in the same period of time.)

We are betting you have a restriction in the cooling passage and by speeding up the engine (& the pump) you are overcoming the restriction.

ps- make sure the belt is tight on the pump!"
 
"Thanks everyone.
It has been

"Thanks everyone.
It has been run in salt water for its 20 years. We disconnected the hose at from oil cooler to thermostat housing at got what appeared to be good flow. Ditto on the exiting the themostat to manifold. By distributing weight of people to the bow we were able to get the stern high enough to visually compare output of water without exhuast blowing into the sea and the water exiting appeared to be the same as the engine that is running fine. Also hooked up freshwater hose to ilet side of manifold and the output looked to be what we expected. not precise measurements by any means, however.
What is the best way to check the elbows for restrictions?"
 
"By measuring their temperatur

"By measuring their temperature. At idle, they should be 150 F or less. Both of them.

Jeff"
 
I recommend purchasing a IR th

I recommend purchasing a IR thermometer. I got mine from Sears about 80.00. Look at the exhaust manifolds. See if they both are reading close. Mine read 135 F or less. Check different spots moving back to the elbows. Check to see if you sucked anything into the tranny cooler or heat exchanger if you have one. I sucked in some seaweed and clogged mine. Installed a sea strainer and fixed that.
With the thermometer you and check to make sure that the gauge is close too.
 
"Okay, thanks for everyone&#39

"Okay, thanks for everyone's input. Good news/ bad news. After more cleaning and swapping the sensor out, the overheating seemed to be under control. We did a short test run and the temp remained good. Bad news- when I checked the oil, it made the milky way look dark. So far I have pumped out over 10 quarts of fluid. Ouch!!

Well the engine is over 20 years old with around 1100 hours. Soooooo, anyone have a spare 305 they aren't using??

But seriously, I do thank everyone for their thoughts and suggestions.

Dave"
 
"Buy a long block 350, or mayb

"Buy a long block 350, or maybe a good used 350. Forget the 305--same weight but less power.

Jeff"
 
"Will a 350 fit in OK and matc

"Will a 350 fit in OK and match with the same tran- VD 1:1? Can the port be a 350 and run with an existing 305 that is fairly new? Recomendations for places to get remanufactured engines? Will Fred get back together withe Claire even tho she is seeing his uncle? (oops , sorry)
Dave"
 
"Dave,
The 305 and the 350

"Dave,
The 305 and the 350 are externally identical,meaning everything will bolt on the 350 from the 305.I'm not sure how it would work having one engine with more power than the other.I'm interested to hear what some of the other guys have to say about that."
 
"Dave,
The 305 and the 350

"Dave,
The 305 and the 350 are externally identical,meaning everything will bolt on the 350 from the 305.I'm not sure how it would work having one engine with more power than the other.I'm interested to hear what some of the other guys have to say about that."
 
"A simple throttle linkage adj

"A simple throttle linkage adjustment is all you need to maintain the same rpms on the bigger engine.


One caution: Later Chevy V-8s (all of them) had a diffferent crank bolt pattern. If so, you'd need a flywheel from THAT motor.

Jeff"
 
Back
Top