mercruiser 165 overheating issue

[Rumley]

Hi everyone,
i have a 1975 mercruiser 165 hp inline 6. The situation i am having is that when i go over 2600 rpm the motor overheats, if i slowdown or stop within a minute or 2 the temp goes right back down. I changed the waterpump/impeller in the outdrive last week. I am curious as to any ideas anyone might have about why it is overheating. If i keep it at 2600 rpm it does not overheat. I am going to install a new thermostat saturday evening and see if that is the problem. I am looking for ideas of what it could be if it is not the thermostat. any help would be greatly appreciated.
thanks
kevin

 

[dirtyoldman]

Re: mercruiser 165 overheating issue

Hi everyone,
i have a 1975 mercruiser 165 hp inline 6. The situation i am having is that when i go over 2600 rpm the motor overheats, if i slowdown or stop within a minute or 2 the temp goes right back down. I changed the waterpump/impeller in the outdrive last week. I am curious as to any ideas anyone might have about why it is overheating. If i keep it at 2600 rpm it does not overheat. I am going to install a new thermostat saturday evening and see if that is the problem. I am looking for ideas of what it could be if it is not the thermostat. any help would be greatly appreciated.
thanks
kevin

It could be a bad thermostat or kinked supply line from the impeller in the outdrive. I would start there, then check compression to see about a head gasket.

 

[Rumley]

Re: mercruiser 165 overheating issue

thanks for the reply, i will check the compression, what should it be?

 

[cr2k]

Re: mercruiser 165 overheating issue

When you changed the impeller was it intact? If not did you get all the pieces out? if not they are causing a restriction between the impeller and the engine. Could be in the thermo housing too. Check the heat exchanger if you have power steering.

 

[dirtyoldman]

Re: mercruiser 165 overheating issue

When you changed the impeller was it intact? If not did you get all the pieces out? if not they are causing a restriction between the impeller and the engine. Could be in the thermo housing too. Check the heat exchanger if you have power steering.

No heat exchanger on that one that I know of. The pieces could be stuck in the thermostat housing, but the system is much simpler than the v8 and other engines as far as the cooling loop goes.

BTW, check the compression last. Those other things are much more likely to be the issue unless you have other symptoms of head gasket issues.

 

[porker99]

Re: mercruiser 165 overheating issue

I had the same issue on my 73 inline 6 165hp. This system is very simple. The water is picked up by the lower unit the feed up the tube to were it temp senser is. I took everything apart. Took the water pump off clean up took the the whole piece that connect to the block were the temp piece is and cleaned it up. I even took the the manifold off and clean up took the rust right off bought a new temp thing and put back to gather and its never run better.

 

[DarrinT]

Re: mercruiser 165 overheating issue

Cracked the head on a mercruiser 140 after changing the impeller and the engine still overheated. The bits of the old impeller were hiding in the bottom of the outdrive water intake where I didn't think to look.(bonehead) Those four small bits of rubber would intermitently clog the intake causing an occasional overheat condition until finally they jigsawed themselves together to totally clog the outlet pipe from the pump and being in the wilds of Georgian Bay with the kids at the time I badly overheated her and wrecked the head to get back to shore.