Johnson 150 overheat

hogan12009

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Apr 4, 2013
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I have a Johnson 150 1995 I think and it overheats. idle for 5 minutes and alarm goes off. Water pressure at idle is 3 pounds maybe and when reved to 4000 at idle pressure goes to 15 or so. I just hooked the alarm back up and I am worried that the engine is damaged I used the boat for ten minutes while it was like this. how long would it take to do serious damage? It does start and run strong. What could be causing the overheat?
 
Joined
Apr 28, 2013
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Re: Johnson 150 overheat

Are you sure its over heating maybe alarm is bad is there anyway to temp temp with gage
 

71Windsor

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Re: Johnson 150 overheat

Pick up a digital thermometer the type with a laser and check your head temps in a few places starting at the thermostat housing. You could get a false alarm. If not atleast you know where and how hot the engines getting. As for how long it will take the answer is not a specific time. Damage can occur in a few minutes or 15 minuets depending on exactly how hot the motors getting. I've overheated an older 150 and had no choice but to baby it in 45 minutes to the dock no damage occurred. Now I could have been extremely lucky or it wasn't getting very very hot I didn't have a temp gun handy so I don't know. But she's still running to this day so I thanked the engine.
 

Chris1956

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Mar 25, 2004
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Re: Johnson 150 overheat

Is that motor a 60* V6 engine? If so, you will see water pressure of 20+PSI at high speed, if the waterpump is good.
 

hogan12009

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Re: Johnson 150 overheat

It is a 60 degree looper. I have two temp gauges and they both went to 200. I could touch the heads for a few seconds and it wasn't hot enough to bubble any paint or cause it to not want to start. Compression test today cylinders approx 105? is this acceptable?

I am thinking it is the impeller maybe from sitting around the impeller dried out? Should i do the whole pump kit or just the impeller?
Brand new temp sensors alarm thermostats and temp gauges.

At 6000 rpm the water psi should be 20? I would think this is low?
 

71Windsor

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Re: Johnson 150 overheat

200 degrees is hot. much to hot. 105psi is acceptable on the cylinders in fact its not bad at all. id recommend a kit its not to much more then your impeller alone and you wont have that moment scratching your head wondering why you didnt get the kit to begin with lol. 20+ lbs is not to low. anything below that would be alarming at those rpm ranges. when it comes to keeping your engine cool even if your into it for 200$ in parts which is ALOT its still cheaper then a rebuild and in alot of cases the tow back in to port.
 

hogan12009

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Re: Johnson 150 overheat

I see the pump kit for 49 on ebay 20 dollar in shipping. the boat is with a mechanic right now and he wants to put only the impeller on and not the whole kit. I am thinking the whole kit should be done. Is there anything else in this engine that would stop it from cooling?
 

71Windsor

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Re: Johnson 150 overheat

Quiet a bit actually. The tube at runs from your impeller to the top of your motor can clog or if the lower unit wasn't assembled correctly it could be bent. Your thermostats could be bad or have some junk packed in there. And the smaller passages through the heads could be restricted. I'd start with the impeller and housing it should be replaced any how I'm sure. Check the tube while your there. Remove your thermostats and check the housings and if you have the money replace them. If not check there functioning as intended and all the passages are clear. Your mechanic should know all of this if he's an marine mech.
 

bakerjw

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Apr 3, 2013
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Re: Johnson 150 overheat

I have a 1990 Evinrude 150 outboard. The first time that I took it out, it didn't seem to be pumping much water.

I went the complete route and replaced the water pump, housing and everything since I had the lower unit dropped. Better safe than sorry imho. Since I already had the lower unit off, I hooked a hose to the water tube that goes up into the block. I took off the thermostat covers and then flushed water up through the block to be sure that there were no constrictions. I then ran water back down the block. The thermostats and gaskets were like $55.00 at the local shop so I replaced them. Cheap insurance.

The next time that I took the boat out, the water stream was impressive. It popped off the hose that feeds the siphon tube in the cowling. Once fixed it put out an impressive stream.
 

hogan12009

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Apr 4, 2013
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Re: Johnson 150 overheat

I have already installed new tstats hoping that would fix the overheat issue. I have minimal water coming out the pee pee hole at idle and I am sure it should be shooting out, boat idles around 1000 rpm little high but i'm not sure if the overheat would cause a high idle or not. Maybe the hot foot needs adjusting. I see boats on youtube really pissing water on the hose so I am sure this is my problem.
 

HenryB

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Dec 8, 2012
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Re: Johnson 150 overheat

Your engine has a fail safe mode that shuts down ignition on one bank if the head reaches a critical temp. It is scary as hell when it happens because the engine feels like its about to blow. But it saves harming the engine. If the engine did not shut down then nothing bad happened. It should idle at around 150 deg. and drop to the low pin at 4000 rpm. Its probably time for a new pump kit. if not done already.

Don't just change the impeller. Install the whole kit. Your pump is probably way over due. Not only is the impeller worn to a frazzle, but the housing, too.
 

hogan12009

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Re: Johnson 150 overheat

The pump is really hard as a rock should it be like this? The boat sat for a very long time long enough fo an animal to make a nest in the jack plate...
 

HenryB

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Re: Johnson 150 overheat

What ever made the nest its children and their children probably used it.

All of your seals are gone, too. Don’t put the thing back together without a complete seal change. You will regret it if you do not do it.

Change the lower unit lube, as well, and use a new gasket under the fill screws.

Oh, and another thing. Pull the "pee" hole tubes and make sure they are clear.
 

hogan12009

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Re: Johnson 150 overheat

I pressure tested the lower unit and it checks out. the fluid was gross from i assume sitting around. Are those the seals you are talking about? pee hole is clear. Ive been reading that the pump has to be soft to make a good seal in the housing to build pressure.
 

HenryB

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Re: Johnson 150 overheat

Part #7 in the diagram, 2 required. They sit just under the pump housing. They are STD bearing seals like the ones on car and trailer axles. They are not very expensive, and the mechanic should have no trouble changing them.

http://www.**********/parts/search/BRP/JOHNSON/1995/J150EXEOM/GEARCASE - COUNTER ROTATION/parts.html

If the fluid you are talking about is the gear lube it’s probably sour from the water in it. Water can enter through the seals as mentioned, or through the bearing carrier (see diagram), again the seals are the automotive type, and a few large “o” rings. Again the mechanic should have no trouble changing them and the cost of the seals and “O” rings is minimal.

You’d be well advised to do a complete seal job now while the lower unit is in the shop.

And again, use fresh gaskets at the fill screws,
 

hogan12009

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Re: Johnson 150 overheat

7 0329922
SEAL, Driveshaft, upper
$7.96 $5.57 1
7 0341280
SEAL, Driveshaft, lower
$12.96 $9.07 1
7 0329923
SEAL, Driveshaft, lower

You mean these ones? I am not sure the lower unit seals are leaking as I have done a pressure test on the LU?
 

71Windsor

Petty Officer 1st Class
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Jun 25, 2008
Messages
286
Re: Johnson 150 overheat

the gear oil in your lower unit shouldn't have been gross. was it milky or discolored? if so you probably had water in there at some point. and a prime example i had a mud wasp build a nest that completely restricted the water intake and when i ran it thinking i got it all out the tell tail had been completely stopped with the remains. and the boat was only out of the water for 2 weeks for maintenance.
 

bakerjw

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Re: Johnson 150 overheat

The pump is really hard as a rock should it be like this? The boat sat for a very long time long enough fo an animal to make a nest in the jack plate...

My impeller felt fine but they lose flexibility with time. Getting the kit is the prudent thing to do and the cost isn't much.

Is your lower installed already? If not, I'd recommend hooking a hose to the water tube with the thermostat covers removed and giving it a good flush. I also flushed back down the block. It is a wet and messy job but it gave me confidence that there were no obstructions.

With the new pump and new thermostats, it pees like a Russian race horse.
 

hogan12009

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Apr 4, 2013
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Re: Johnson 150 overheat

Got the water pump in and it's pumping water now but the head gaskets are now leaking on port side. But both banks are heating up still . would the leak on one side cause both banks to overheat? Looks like some bad silicone on port side. Haven't taken head off other side yet.....pistons look new but gaskets thermo seats look old so whoever rebuilt it re used the originals it seems
 
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