85 Yamaha overheating

I have a 85 Yamaha that is overheating. The engine was built in 1991. The ports in the engine are clogged with salt etc. like cement. The engine only overheats in the middle of summer. I changed the water pump and thermostats at the end of last summer. No problems last winter. The water is now near 90 degrees and the engine is over heating again. If I run at 4000 rpms the engine will not over heat. I cruise at 4800 rpms and never above. I don't want to remove the covers and break bolts. Can I remove the thermostats in the summer and replace when winter comes.<br /><br />Regards

Re: 85 Yamaha overheating

I was hoping someone could comment on the above. The motor is a 91 model and has never seen a shop. I don't want to unbolt any covers and break bolts. Is it OK to run without a thermostat?<br /><br />Any help would be appreciated.

Re: 85 Yamaha overheating

Since i'm not a pro ,you can consider this .....It sounds to me your engine can get you into a jam coming soon ,and considering the heat on the water,,,,,wow. Do a search on "popit valve" and the cleaning of it,as it may be partially stuck open.I'm not sure on the thermostats being left out,so hopefully someone else will reply.If your determined to keep the engine, find out the cause of the overheat,but from what you said so far, the cooling passage ways are clogging.

Re: 85 Yamaha overheating

Thanks for responding. Where is the Popit valve located? There is a spring loaded valve under the thermostat that looks like it lets more water into the system at high speeds. Is this what you are talking about?<br /><br />Also, my 85 Yamaha is a 91 model and has never been in the shop. Not once. I fish 2-3 times month in salt water. The summer water being almost 90 degrees is when it happens.

Re: 85 Yamaha overheating

I believe that the prognosis is not good. There is a high probability that the problem is entirely due to the salt clogged cooling passages. Salt is a pretty good insulator and will not allow the engine heat to pass through into the cooling water to be expelled as waste heat. <br />There are some chemicals (Names disremembered) that can be used to partially dissolve the salt but they are also hard on the engine materials. Chipping the salt out mechanically doesn't work either cause some of the passages cannot be reached by a pick. Probably best to dissassemble and take the parts to a machine shop for a caustic bath.<br />Check with the machine shops about the practicality of this approach before you dissassemble your engine though.

Re: 85 Yamaha overheating

The popit valve is a pressure relief valve. That and the thermostat could both be defective. You can test the thermostat in hot water to see if it opens and then closes in cold water.The housing for these will require a good clean. You can run without a thermostat especially in warm water but you may get more sparkplug fouling.

Re: 85 Yamaha overheating

Are salt deposits actually visible on the exhaust ports or are you referring to some other part of the engine? How did you visualize this if you didn't remove any covers? There should be no water in direct contact with the exhaust (or intake) ports. If there are deposits on the ports, that is probably the root of your problem. One of the causes of high rpm overheating is a leaking head gasket. The only fix is to pull the head. Not a big deal if the bolts come out. Bigger deal if they won't.