Firstly, many thanks to everybody for the top replies and suggestions, certainly helps me narrow down the issues!
OK, just to clarify what was done to this motor:
Rebuild of everything internally in the motor, pistons and all their associated bits, new PORT cylinder head, new manifolds and exhaust risers on BOTH SIDES! Hoses etc all replaced and every accessory from salt water pump, starter etc. etc. pulled apart and serviced. Also the Stern drive (Volvo) was thoroughly checked and found in good condition throughout. New bellows fitted, Unis all fine, new impeller and housing and all marinised gaskets fitted throughout! So, to the overheating problem!
Note: NEW = side of donk with new cylinder head, OLD is the other ..........
At idle and up to around 3,000 rpm, temp is normal at some 60-70 C though even at this stage the STBD side is already about 10C higher .......... Increase in power by as little as 300 rpm causes full scale increase of temp on gauge to 100C and that is confirmed by external IR Thermometer. The NEW side maxes at 75C but the STBD - old side) hits the 100!
Out on the water, while the temp was pretty normal, I briefly took off every water pipe from the stern drive intake to the saltwater pump, outlet to the thermostat housing, both outlets to both manifolds and you could put out a fire with the water gushing out of each one (same result with earmuffs and hose at pontoon). In fact jusr loosening the hose clamps had water bursting out of the pipe ends before their removal,
Pushing up the revs by 300, immediate full temp! Conversely, pull them back by a small amount and the temp falls back off the clock! Crazy!
Pulled off the hoses completely off again during high temp reading and ............ water, water everywhere! The inlet hose to the high temp OLD side had more than enough cool water pouring into it!
So, is it just a tight and new motor causing the problem but why would the OLD side be effected so dramatically? The gauge and sender can be ruled out as my hand held IR thermometer confirms the temps are genuine!
Having said the above, is 90-95C too hot for a new tight motor? Maybe it's normal! Don't even want to think why the OLD side is heating up all by itself though!!!
I'm stuffed guys! Over to the experts!
Did this do this before the rebuild?
Why was it rebuilt?
Is the engine standard rotation? Is it possible a new water circulation pump has found its way on there and suits the wrong rotation?
If the engine features a serpentine drive belt for accessories is it routed correctly and not spinning the circulation pump backwards?
Im not wanting to send you on wild goose chases but weirder things have happened.
Where is the boat?
Just cruising the web there is some talk of both thermostats and head gaskets being able to be installed back to front with both resulting in heating issues. So is this thing purely saltwater cooled or do you have a heat exchanger and a fresh water pump as well?
Had a cracked cylinder, scored bore and twenty years old so close to its end!Originally Posted by The Woo
Never overheated in its entire life, ran for over twenty years at 60-70 C
Yep, standard clockwise rotation, same old water pump with new impeller, nothing altered and is putting out huge amounts of water at all revs. Belt rotation is normal old pulleys and nothing special about the set up, all new belts?
Thanks for suggestions, much appreciated!
Thanks Scotar! I've had the thermostat both in and out and the effect is still the same overheating. It's purely salt water cooled via the leg impeller and then the pump itself. Even when it is overheating, the
pump is putting out huge amounts of water to both manifolds though just looking at the water flow I guess doesn't mean it is enough. Same old question though, why does ,and extra 300 rpm have such a dramatic effect? Doesn't make sense! Add 2-300 rpm and the temp gauge goes to maximum!
i can run all day long at around 3,000 rpm and the temp is fine, nudge it up a bit, goes bloody mad!
Purely speculation and imagination below....
Just thinking - if the rise and fall on the old head is pretty immediate, in the space of a few seconds? Could it be a head gasket/cracked head leaking pressure from the cylinder to the cooling jacket? Are the compressions OK?, is there a way to check for bubbles in the risers/cooling circuit when pressurising the cylinders one by one? Just thinking the thermal mass of water and steel should take more than a few seconds to change a large amount 80-100 deg?. If the water in the head gets blown out enough from leakage from the cylinder, the cooling effectiveness could drop right off. Once RPM is reduced a little, less air is getting pushed in and there is enough water to cool things down again. ??
From a relatively cold engine, what does it do when going up to 3300rpm - does the old side ramp up just as quick as if the motor was already warmed up at normal temp?
Total inboard ignorance below:
Is there a way to do a test like on old cars, looking for bubbling in the radiator?.. maybe a looped cooling circuit with a tee in it so you can see if pressure is getting forced in ?
Random thought #2, If the fuel economy is a lot better (25%) than the old, and idles fast etc- could it also be running lean and starting to ping with at higher power?
As for old side being hotter under power - skimmed head = higher compression ratio = more ping chance? --- is there any noticeable difference in plug colour between any plugs - are the plugs running hot or normal colour on the insulator?
Is it an easy thing to richen the mixture a bit to see if there's any difference?
Also for timing - not sure which way would make it run cooler - advance? slightly and see if there is any change? -- does it have a distributor with vacuum advance, is all that working OK?
Wishing you good luck in solving the problems!...
Being off the water, or on the water at less than full power is no fun!
I guess it doesn't have some sort of bypass/diverter/poppit valve setup like outboards do? Symptoms are very poppit valve like! Failing that, best guess is "something" jammed in the cooling passage, possibly near the temp sensor, letting enough water through below 3,000RPM, but not above.
Do a compression test if not already done and see what that shows up. Look at plugs for any differences between each bank.
If base timing is out as in too advanced it could be pinging and increasing the temps and destroying your motor.
Also pressure test the cooling system if you can to ascertain if there is a leak somewhere.
What type of cooling system is it again? Are the block, heads closed freshwater circuit and manifolds saltwater cooled? Were all the rubber coolant hoses replaced or inspected or original (sometimes issues with hoses loosing shape and sucked in reducing flow at higher rpm ? Where are you measuring the temp? From the original sender or just a heat gun?
Given that it is saltwater cooled, I would almost be inclined to think you have a blockage somewhere either due to an impellor previously failing or simply salt and corrosion build up. I would have thought that an engine that was designed originally to run on a closed cooling system would have a hard time getting hot at all with the thermostat out and cold water continually coming in. You did check to make sure the head gaskets were in the right way?
Two things first! I really appreciate the replies from everybody on this issue! The suggestions have been great and have helped me a great deal to try and track down the problem.
Secondly, my apologies for not getting back speedily enough to the replies! Unfortunately I had to make a medical emergency trip to Adelaide that took a couple of weeks but with good results ........
OK, same problem i.e. Overheating of starboard manifold! I have done numerous checks following all the suggestions from you guys and I am 99% convinced this "mechanic" (for want of a better word) has put the head gasket in upside down or maybe the wrong one even! Or there is a serious blockage in there somewhere?
I have pulled ALL the water hoses off one by one at idle, normal 3000 rpm (no overheating) and 3,300 rpm (instantaneous overheating) and the water flow from them all is enough to fight fires! So it seems to me the water from the impeller and sea water pump is more than enough to do the job but it's just not getting to the head properly i.e. Gasket fitted wrong way?
I even - very briefly - blocked off the water intake to the "cold starboard manifold" and the exiting water via the leg was still pretty strong though damned hot as you would expect!
So I'm going to have to dismantle the whole starboard side and see what is going on!
And you may well ask "what is the mechanic doing to help?"
Not a thing! He has disowned the entire problem saying he was only responsible for rebuilding the motor! Other problems weren't of his doing! Any criticism will incur legal action! Not the sharpest knife in the drawer this guy!
So, thanks again and I'll get back with any progress!
Take pictures and have a witness. If the gasket is upside down try to leave it attached to the head and take it to him.
Got that thanks! Already have a pic of a piece of wire used to hold the throttle linkage to the carby instead of a cotter pin, consequently fell out and left me with no power when I needed it, also fully threaded bolts used to bolt starter motor on. Threads chewed out the alloy holes and the pinion gear moved out of range of ring gear, numerous wires just cut off and left hanging, several gauges not working ........... It's been a ton of fun so far!
I know nothing of marine engine cooling but it sounds similar to a car cooling problem where with just a few more revs it overheats. In a car the bottom radiator hose has a spring inside it that stops the hose compressing when engine revs increase. If the spring rusts away or goes missing then the hose compresses reducing flow and it overheats with just a few 100 revs more.
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