Reply With QuoteHow many hours on the engine? How's the timing? How does the water flow look when you are on the trailer (hose)? When the revs come up, does it overheat on the trailer, or only under load?
If you have restricted flow, maybe sand in the block?
Have a deep vee cobalt with 260 mercruiser and alpha drive, engine is 350 with comp cam, edlebrock manifold and 650 holley, the rest is stock. Will run all day idling and easing around, but within minutes of going full throttle the temp starts climbing fast. The impeller, engine water pump and thermostat are all new this year. Any suggestions? Help please.
How many hours on the engine? How's the timing? How does the water flow look when you are on the trailer (hose)? When the revs come up, does it overheat on the trailer, or only under load?
If you have restricted flow, maybe sand in the block?
The motor is new, has maybe 3 or 4 hours on it. Block was boiled out. Timing is set a 8 btdc at idle, havent been able to get a high rpm reading yet. Is the stock distributor with pertronix kit installed. I've been thinking I should go back to the points. I ran the engine the first couple of hours with the points and dont remember the temp climbing but the wide open blasts only lasted seconds on the new motor.
19cobaltcd:
I've been thinking I should go back to the points. I ran the engine the first couple of hours with the points and dont remember the temp climbing but the wide open blasts only lasted seconds on the new motor. Temp climbing could be timing, not sure about the points (pinging?). Same heat range on the plugs? Is the sender on the head or the intake manifold?
What's your compression? I think overheating could be caused by bad cam timing or pingng on a new motor.
Sounds like the flow should be fine, unless someone ran the engine without water for a few seconds with the new impeller. Either way, it couldn't hurt to check it (once the motor is broken in)...just see how much water comes out the exhaust on the traler at higher RPMs.
Could your pump be sucking air anywhere?
The compression is still stock, a little under 9 to 1 I think. Its a '79 model. The block and heads were decked in the rebuild but mininums were taken off. Water flow on the hose seems to be fine, the temp never wavers on it, the sending unit is in the manifold. I burn premium gas only in it. The only other difference since break in is the prop, went from 3 blade ss 21p to 5 blade ss 19p. RPM with the 19 wide open was about 4600. The boat dosent care much about trim (carries the nose high anyway so I dont trim it out much. It is alot harder to start with the electronic ignition. The points fired first time, every time. The rpm went up about 500 rpm with the 19p but I lost about 4 mph at top end.
So it sounds like the load is causing the overheating.
That ignition sounds a little sketchy...I agree...that would probably be the next thing I'd check. Maybe throw a timing light on there at over 3,000 RPMs, just to be sure.
i think the over heating thing might have some thing to do with a lean fuel mixture along with some of the other things mentioned above. do you have a fuel presure gauge?whats it's do when you open the throttle wide for a minute? any back fire type sounds when you back off the throttle ?could be a sign.just my .02 good luck with her.
[ July 10, 2003, 09:25 PM: Message edited by: bordsmnj ]
I had this same problem on my 7.4 mpi motor and did all the things that you have done, impeller, thermostat excetra. The problem wound up being a plugged oil cooler. Make sure all your water passages are clear. Flushing did no good I had to take all hoses and oil cooler out to clean. Sand and pebbels were packed in so tight that I had to knock them out with a steel rod. Weird thing is it just starting overheating in the middle of the lake after running all day. Just my .02
We had the same prob,on our boat most of the time it is the risers,replace them and your prob will go away
Later Stan
It sure sounds like you have a water flow problem. RESTRICTION some where. Could be manifolds or oil cooler plugged if you run a oil cooler. You could put a tee in water line to manifolds with a valve and try and bleed off some of the pressure as a test. I doupt it would be manifolds unless they have been run in salt water or a OLD. Do you have or can you hook up a gauge to check your water pressure. Alpha has water pump in the drive any chance a hose is pinched or colapsing on the supply? I don't really like the Alpha water pump but if set up correctly I know of several feeding big blocks so your small block should not be a problem. I have seen bad thermostats you might try testing yours or take it out long enough to make a couple hard runs. Sorry not much direct help. Let us know what you find. I still betting on a water flow problem. Good luck. Just my .02 smile_sp
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