merc 135 running hot

[bebob25]

I have a 1986 mercury 135 that runs hot and we cannot figure out why? change all the obvious parts but no success. Even changed timing trigger, head gaskets, pulled exhaust and ran a different lower unit. compression checks over 100 on all cylinders. pumps great but runs hot when u get on it. comes down when you let off. Any advise need help please

 

[Chris1956]

Re: merc 135 running hot

Can you tell us what the obvious parts are? Normally they are waterpump impeller, wearplate and all gaskets, thermostats and poppit valve. Did you get all these?

 

[boben2830]

Re: merc 135 running hot

Check the thermostat !!

 

[sschefer]

Re: merc 135 running hot

Am I understanding correctly that the problem does not occur at idle?

 

[bebob25]

Re: merc 135 running hot

Yes, waterpump, even housing unit, poppit valve, fuel pump, temp sending units, pickup tube seal, new carb kits, water jackets. Practically new motor. It runs cool at idle but when at 3000 rpm it pegs hot. When you let off it cools again. There is no corrosion or blockage as said and it pees great. Thanks for replies really need to figure this problem out.

 

[bebob25]

Re: merc 135 running hot

Also i forgot. t stats changed also

 

[j_martin]

Re: merc 135 running hot

Yes, waterpump, even housing unit, poppit valve, fuel pump, temp sending units, pickup tube seal, new carb kits, water jackets. Practically new motor. It runs cool at idle but when at 3000 rpm it pegs hot. When you let off it cools again. There is no corrosion or blockage as said and it pees great. Thanks for replies really need to figure this problem out.

There is blockage somewhere. Water exits the block from multiple places, some are open all the time, some are controlled by thermostats, and one is controlled by the poppet.

It would help to have a pressure gauge on it and know what the pressure is at various engine speeds.

John

 

[sschefer]

Re: merc 135 running hot

The problem is in the poppet valve area. The remainder of your cooling system is working correctly. The thermostat openings are not sufficient to keep up with the cooling requirements after about 2500-3000 RPM's.

Look into the block at the poppet and see if the plastic insert and rubber grommet are in place. If you didn't change these when you rebuilt the poppet valve and you notice that the rubber grommet is missing then it's fallen into the block and that's where you blockage is.

If the block side looks o.k. then you've assembled the poppet incorrectly and it is not opening.

 

[Jacket4life]

Re: merc 135 running hot

Hey, I'm probably out of my league, but something that will seem stupid, but maybe???

Do you have a gauge or just a warning buzzer? What I wonder is, does the engine actually get hot, or maybe the sending unit is just screwed up? Just throwing it out there....

If the engine is actually running hot, you can't put your hand on the cowl while it's hot.

 

[Faztbullet]

Re: merc 135 running hot

This engine has the old style poppet valve and it will be either in the poppet or divider plate clogged with debris. Water enters to cool cylinders thru divider 1st then cly head and to t-stats and poppet. If you need diagram pm me...

 

[bebob25]

Re: merc 135 running hot

Thanks for all replies and I have 1 more question. If the poppet is working properly should water flow out of the exhaust ports? I am checking the poppit valve again.

 

[shadetree1]

Re: merc 135 running hot

I just got done working on a 60 that was from what I can tell doing the same thing....ended up being the timing was way advanced in the high range adjusted it back to specs and not a problem since!