Hi,<br />Any suggestion what to try next with my Suzuki DT 65 (65 hp) outboard that is running hot at high rpm?<br /><br />A. Some background info:<br />- The Suzuki DT 65 was made in 1991 and has been runnning about 150 hours since then.<br />- My outboard has only been used in fresh water (never salt water).<br />- Last year I had it in at a Suzuki marine service shop and I got a new impeller and some other things(for example new rubber gaskets in both ends of the pipe that goes from waterpump and up in engine).<br />- Last week it developed an overheat problem at high rpm only and the overheat alarm goes on. It can be repeated every time now when I run at higher rpm for maybe 5 minutes or so.<br />- There is plenty of water spraying out from water outlet and the smaller water outlet(that spray to the side).<br /><br />B. So, what I have tried so far:<br />1) Since the impeller is new I guess it can not be that (it was mounted by a Suzuki service center so it is probably mounted correct). I have almost not used the engine since the new impeller. (Gasket was new also by the way.)<br />2) I changed the thermostat to a new one some days ago. Made no diffrence. The thermostat is mounted as per instructions in manual (vent hole pointing towards the direction of spark plug).<br />3) Tried a new temp/waterflow sender. Made no diffrence.<br /><br />As an experiment I run the engine without engine cover to feel with my hand how hot the cylinder heads get and after the engine overheat alarm has sounded and I put my hand on it it is rather hot (not so I burn my hand since I can keep the hand on the cylinder head without needing to take the fingers away).<br /><br />4) I took out the theromstat completely(running without thermostat) and mounted the thermostatcover and then I notice this:<br />a) There is slightly more water spraying out from water outlet and the smaller water outlet(that spray to the side) is about the same as before.<br />b) Engine is running MUCH cooler and I can run the engine at full throttle (about 5400 rpm) as long as I want without any overheat problems/alarm.<br />c) Mounting back the new thermostat and running the engine at high rpm overheat the engine.<br /><br />As an experiment I took the old thermostat, that had no fault obviously, and drilled 3 small 3 mm (millimeter) holes through it just to see if that made no diffrence. Yes, the engine run much cooler and no problem with overheat at high rpm.<br /><br />I have Suzuki manuals (Selco and Clymer, thick ones...) and there are some suggestions for troubleshooting overheat problems.<br />But I'm not sure what to try next.<br /><br />I suspect some blockage (sand, mud or something) in cooling system somewhere but note sure how to clean it out.<br />- High water pressure - in reverse direction, how?<br />- Air pressure the blockage out -how?<br />- Or must the engine be taken apart ...?<br /><br />What is confusing is the fact there is plenty of water spraying out from water outlet and the smaller water outlet(that spray to the side) so there is obviously water circulating.<br />And the thermostat experiment - what conclusion can be made out of that?<br />I have checked the main water intake and no blockage there, same with the other intake behind and above the prop.<br /><br />Thanks for any assistance.<br />/Bo
