Engine Overheating

[kwoolard]

Re: Engine Overheating

Well, after trying out a lower pitch prop the overheating problem still exists. Although, I could get about 3700 rpms out of it with better hole shot. <br /><br />However, I am still stumped on my overheating problem. I ran the engine without the thermostat and the temp gauge read about 160 at WOT. I know the water flow is good. I checked my timing this weekend at it was at about 11 degrees, and I think that the recommended is 10. A local boat mechanic said to drop the timing another 2 degrees, he stated it helped him run almost 30 degrees cooler. Hard to believe that a couple of degrees would do that. <br /><br />I am running out of things to try. Could I have an exhaust restriction, which could also be the reason why I can't get over 3700 rpms? Could my circulating pump be bad, how would you tell without removal? Would retarding my timing by two degrees help or hurt? The engine doesn't seem to spark knock at high rpms or under a load, so I don't think that it is the timing?<br /><br />Anymore help would be much appreciated.<br /><br />Thanks again for everyone who has posted so far.

 

[kwoolard]

Re: Engine Overheating

Any ideas as to why the engine would be running this hot without a thermostat installed?<br /><br />What is the best method for checking a blown head gasket?<br /><br />Would broken mechanical advance distributor springs cause the motor to overheat this much?

 

[yoced]

Re: Engine Overheating

Yes, broken distributor springs will cause havok with your temperature. Firing at wrong time is always a bad idea.<br /><br />Taking the thermostat out will never help your engine unless the thermostat itself is bad. The only thing you are hoping to do by taking it out is to hide the problem temporarily.<br /><br />An exhaust blockage would be a problem, but I would think it would be very noticeable on your boat. You can always take a look.<br /><br />Your circulator pump must be working, as you claim to know you have good flow! <br /><br />I think if you fix your RPM problem you will fix your heating problem. Everything you tell us leads me to believe that your cooling system is working just fine, but that you are running your engine too hard for too little result. I don't know what the real mechanics on the forum would say, but I would start looking at your timing system - from the cam chain to the distributor. I know my local guru would start by checking the simple physical things like trim and barnacles..

 

[cobra 3.0]

Re: Engine Overheating

Are you always giving readings from your laser heat gun? In any case, 175 degrees isn't that hot. Closed systems operate at higher temps than this. If your risers are warm to the touch (you can keep your hands on for a few seconds) your system is operating fine. <br /><br />I'd try a 15" pitch prop to try to get your rpm's up near the top end of your rpm range. You are still somewhat lugging your engine.

 

[kwoolard]

Re: Engine Overheating

One more thing, I probably know the answer to this but I will ask. Is it normal to be running say at 165 degrees, and the temperature rising to 190-200 degrees once the engine has been cut off? I assume this is because the water flow is stopped and what water is sitting there is just absorbing heat from the engine. If it is not normal, is it an indication of steam in the water lines?

 

[Peter J Fraser]

Re: Engine Overheating

Kwoolard,<br />You are right on the last post.<br />Its called "Latent Heat Soak" and is caused by the latent heat that is contained in the upper cylinder areas slowly 'soaking away' and into the cooling system.<br />Because your Temp sender is usually fitted just below the thermostat it shows as a rise in temp after the engine is shut down.<br />You can reduce the effect by allowing the engine to idle a little while after it has been run under load.<br />Good example of this is a trucker who will let his engine run for upto 10 minutes at idle before shutting down.<br />Remember also that your engine is running inside an enclosed space with very little cool air around it to assist the cool down process.<br /><br />Good luck,<br />Peter

 

[gdburch]

Re: Engine Overheating

kwoolard I just found your post and I also have an 888 that is running warmer than I like. Mine is a 1974 in a 19' Sabercraft hardtop. It runs about 175 wot 3800rpm and about 165 at 2800. Last year it ran 155 no matter what I did. It acts the same and I'm getting the same or slightly more rpms out of it with the same prop as last year. I've replaced the outdrive water pump and hose between drive and transom along with rodding out the risers and replacing the thermostat. Next is timing since I just found my timing light. I'll let you know if that helps. <br /><br />Also you asked about exhaust backpressure and mine does blow exhaust out the hose fittings on the risers when the hose is removed. I figured this is normal.

 

[kwoolard]

Re: Engine Overheating

Thanks PETERF, I felt that was the case.<br /><br />GDBURCH, keep me posted on your overheating issue. Also, is your timing mark a cast in type needle/prong or is it a timing tab? I think that is what I have, however, it is broken and the only thing left is a short piece sticking out of the block. Keep in mind my the latest temperature readings I gave were running the engine without the thermostat. With the thermostat installed the engine runs much hotter, somewhere around 190-200.<br /><br />Another question, will reducing the pitch of the prop by two more inches reduce the running temperature 35 degrees? The engine doesn't seem to be lugging with the 17 pitch prop, however, if it will lower the operating temperature I am willing to try anything.<br /><br />What is the best method for checking a blown head gasket....clear hose between the T-Stat housing and the riser?<br /><br />The engine is also really hard to start cold and a lot of times when it is hot. I usually have to pump the throttle a couple of times to dump fuel into the carb throat, once it starts I run it at a fast idle. If I don't let it idle fast and just bring the throttle back to the nuetral position it will just idle down and cut off. I am not sure if this has anything to do with the timing, which in turn could cause my engine to run hot.