Changed lower unit now overheating

[adam98]

I have an 89 xr4 150hp 2.4l that runs perfect after lots of parts and trouble shooting. After a year my 1.78 3.75" lower unit stared kicking out of gear and after taking apart needs new forward and reverse gear for $1800for parts. So I got a 1.87 4" lower unit, fits, shifts and works great on the water,
but my water pressure barely gets pumping and pee stream will kinda pee mixed with exhaust air and or just stop all together. 0-3psi After checking everything in the block everything is fine. Changed water pump and nothing better. Put old lower unit back on and pumps water great 4-10psi strong even with same water pump and housing. Both lower units measure same and copper tube has same seals and length.
So,I Can't figure out how air is getting in water at the pump or tube going up to block... Put all parts back old lower unit and works fine

 

[Grub54891]

Re: Changed lower unit now overheating

Check for an obstruction in the tube,or a warped lower housing on the new l unit. The tube is the same length,is the diameter the same?

 

[adam98]

Re: Changed lower unit now overheating

It's the same tube I swapped over , same pump, no obstructions in block or lower unit pickups or tunnels. Have checked visually and with flow of water.
Put same pump and tube back on old unit and pumps fine.

 

[adam98]

Re: Changed lower unit now overheating

Tube measures same height after installed on both units. Hmm... maybe a suction air leak on the pump, but same pump put back on old unit works

 

[Chris1956]

Re: Changed lower unit now overheating

Did you check for an obstruction in the water intake chamber, under the water pump base? My mercruiser gearcase water intake chamber used to get fill of barnacles, and keep the water from flowing to the pump.

Is the water pump base new?

 

[adam98]

Re: Changed lower unit now overheating

Lower chamber clear, but base was new a few months ago, change to a new lower unit and air water spitting out pee stream. So I took complete pump and tube off old unit and same problem. Put stuff back on old gear case and pumps fine. I keep taking it apart but maybe I'll try a BRAND NEW pump and base... It has to be from the tube down and that's not very much to check

 

[CharlieB]

Re: Changed lower unit now overheating

Many of the V-6's the P stream come off just after the T stats, a cold motor with stats closed will not P at all til it warms and the stats open.

Air coming out of the P tube is an indicator that one of the cyl head gaskets is leaking combustion gases into the cooling system, displacing cooling water, and the motor begins heating up. The cooling system pressure will drop because it doesn't seem to register the combustion gases.

You will need to pull the cyl heads and look very carefully at the gaskets to see where they are leaking. Check the heads for straightness, if warped, have them milled flat.

Compression will be raised slightly depending how much material is taken off the heads, so have both heads done the same. You can raise compression to near 140 without a problem other than needing premium grade gas. You will notice an improvement in holeshot power.

 

[adam98]

Re: Changed lower unit now overheating

That's what I would think also, thanks for the input. But after I put old lower unit back on everything is back to normal...so it's something down low, or at least ill hope for now.
So I picked up a complete water pump kit to start fresh and hope that helps. I read another guy had his in/out of the dealer for a year with these issues and then changed good looking parts and solved his issue. For some reason these outboards are so so sensitive that perfectly good looking used gaskets are not good enough. I rebuilt the carbs many times before I spent the $120 on new gaskets that solved my start and idle inconsistencies. So for anyone else trying to track down issues, if you take it apart, buy new gaskets

 

[adam98]

Re: Changed lower unit now overheating

So put a completely new water pump on a water pressure is back! Idle2-4 psi and 8 psi at 2k rpm. This has been multiple times that on this stinking xr4 outboard that gaskets are not reusable. when everything looks good and you still have an issue. Buy new gaskets! Even my stator read within spec. With correct tools. But changed it out and fixed the issues. Now I know why most mechanic's throw new parts at old outboards
Good thing I enjoy working on this thing... But my 78' Johnson 115 and 95 evinrude 150 have lower perf but are more reliable an quite

89xr4 150 2.4l so far changed stator, cdi box's, spark plugs, oil tank cap cracked, small 1.78 3.75" lower unit gears won't hold anymore, new 1.87 4" lower unit and prop, fuel bulb, air leak at quick fuel connection changed, batteries, carb rebuild kits, gear oil, oil tank check valve bad = fuel goes up into oil tank, fuel pump rebuild kit. Wow maybe I should sell it...

 

[CharlieB]

Re: Changed lower unit now overheating

What, you just got it running well and you want to get rid of it? Blasphemy!

Lots of guys would want that motor, I would think you should enjoy your labors and run it. Now that you have it dialed in it should last you a goodly number of years with simply maint and regular water pump rebuilds, just to be sure.