88 Yam 70 overheating@ high RPMs

[betag2]

I have a 1988 70 yamaha that is over heating at high rpm. It alarms above 4000rpm. I can run the thing all day along under 4000 rpm. I replaced the water pump and thermostat. I also checked the thermodisc it's ok. what else should i do. Motor runs and starts great. Thanks for all and any advice.<br />Bruce

 

[jim dozier]

Re: 88 Yam 70 overheating@ high RPMs

Leaking head gaskets may present as an overheat at higher rpms. Do a compression check and also examine the spark plugs for cleaner than normal plugs indicative of a water leak.

 

[betag2]

Re: 88 Yam 70 overheating@ high RPMs

the compression is top 130psi, middle 125psi, bottom 122psi. Do these numbers seem ok. <br />thanks for the quick reply.<br />bruce

 

[jim dozier]

Re: 88 Yam 70 overheating@ high RPMs

The compression numbers are OK, but a leaking head gasket doesn't always show up on a compression test. Are any of the spark plugs really clean? Have you always had this problem or did it just show up? You might want to verify that the engine is in fact overheating. You can buy a point and shoot infrared thermometer at Radio Shack for about $50 to check the cylinder head temps. If in fact it is overheating you may want check the carbs for too lean a mixture and the maximum ignition timing. When you replaced the impeller, did you check the water pump housing for signs of wear? You may have to go and pull the heads. Buy a manual. Its not hard if the bolts don't snap off (that can be dealt with too). Check for old pieces of impeller in the cooling pasages when the head is off. Make sure you torque the head bolts to manual specs.

 

[betag2]

Re: 88 Yam 70 overheating@ high RPMs

this just showed up. What would you do next. The motor is actaully getting hot. I replaced the impeller and the metal housing it fits into. Should I check the water pressure, If so do you have any suggestions on how. How can I tell if the carbs are too lean. I thought maybe running some 50:1 mix gas with another tank. Just don't know what to do next??? I have a good mechanical appitude and have temp and pressure measuring tools. Thanks again for your help.

 

[jim dozier]

Re: 88 Yam 70 overheating@ high RPMs

Rodbolt's suggestion in your other post is what I'd agree with. (By the way don't start another post on the same subject, its like dating 2 women at the same time, hard to keep your stories straight). Pull the head and have the mating surface machined. Install a new head gasket and torque the bolts to manual specs. This is an easy job if the bolts come out easy.

 

[betag2]

Re: 88 Yam 70 overheating@ high RPMs

Sorry About the doudle dating, I'm new to this.<br />Thanks for the info. I'll be tearing it down this week. Thanks again for the replies.