1987 merc.200hp blackmax cooling problems

i have been haveing aterrible time trying to figure this out.i changed the impeller. i also hve checked 2 more times to be sure that it was done corectly.changed both thermostats; all hoses.even removed lower unit and back flushed the motor.it did get better since i bought the motor but not good enough.im not exactly sure about the poppit valve there was no trash or anything.i just removed my head gaskets today.did not see any problems.motor looks prety clean. any more ideas? thanks.

Re: 1987 merc.200hp blackmax cooling problems

Can you tell me what it does, and everything that you have done so far. Just finished 85 200hp rebuild. Found a whole lot of interesting facts about cooling problems and what to look for. Graduate: "School of hard knocks" 80+ mph kaywilli@iland.net

Re: 1987 merc.200hp blackmax cooling problems

hello trumanlake.i have changed impeler:all hoses;both thermstats;and head gaskets.i checked the poppit valve.i dont realy know what to look for on that.i havent tried the motor yet since i chaned head gaskets.water from the telltal was very hot and gauge reads 200 at idle shoots right up when you give it gas.i have back flushed the motor.got some peices of the old impeler out.pumps alittle better but notgood enough.dont want t run until i get this figurd out.motor has good compression.thanks foryour help the col.

Re: 1987 merc.200hp blackmax cooling problems

Are you getting an overheat alarm when at full throttle? Is your water stream constant or does it seam to spurt or vary in amount at a constant RPM range? Are you still running of the oil injection system or straight 50-1 mix? Are you sure that your Alarm is working, it notifies you if either the oil injection fails or the temp goes above normal.<br />Just a few more questions that may help...<br />I have a 1987 Merc. 175 Black Max and a lot of your symptoms sound similar to what I have on my motor...

Re: 1987 merc.200hp blackmax cooling problems

i dont have any alarms at all.except gauges.i am still using oil injection but was thinking of going to premix.i beleive it is still working but i just dont trust it.i had no water pumping at all now that it pumps it is hot and temp says 200at idle so i know something is not right.motor runs good im just afraid to keep running it.i dont want to damage anything.thanks for info

Re: 1987 merc.200hp blackmax cooling problems

Since you got pieces of your old impeller by back flushing, I would tend to think you still have some blockages somewhere in the system. I am not a marine mechanic, so I have no idea how you would go about clearing them. Just more to think about.

Re: 1987 merc.200hp blackmax cooling problems

(this is what i'd do at this point) This is only a suggestion, I would pull the lower unit again and set it aside, then pull the block off and make sure the water tube is not plugged by running a piece off say 12 gauge wire down through the water tube. There may just be a piece off the impeller stuck there or the grommet is blocking the water. I tend to think the block is probably clean. The block only has 8 nuts (if i remember correctly) holding it. It really wouldn't be that hard if you have access to a motor hoist or a cherry picker. I believe I would also (if you have a air compressor) apply a little air pressure (20 psi) to the tube at the grommet end and block the other end that goes to the water pump and see if there is a crack in the tube (that is also a possibility). While the block is off remove the thermostats and the poppet valve and back flush, just for good measure. Wished you were alot closer, have all the tools would love to help. Keep me posted, my email address is above if you have any questions feel free.