Help! Stumped! 90HP Overheating!

[apaulos]

I've stumped...

My 93' 88HP keeps overheating. I've tried everything: replaced entire pump assy twice, the entire stats assy twice. It's the port side sensor that is kicking off. I've pulled the heads and checked the temperature that the sensors open and close. Both sensors were right on spec. I checked the rubber deflectors and no signs of bulging or overheating. Compression is dead even and all four plugs, pistons and chambers look the same. I checked the timing and it is to spec. I even tried to roll the timing back some. Just seems that the port side runs a little too hot.

Basic scenario: Motor runs perfect except, at idle on the water or on muffs the engine runs real hot. Once under way and on plane (3000+ rpms) for about 5 minutes or so, the port side sensor causes the overheat horn to go on. Once the horn kicks on, I throttle back to idle and let the engine run in gear til the horn goes off. Typically, a minute or two. If I run the engine with the cover off, it takes longer for the alarm to go on and less time for it to go off.

When I pulled the heads off, I noticed lots of scaling on both the heads and the water passages in the block. I need to research how to get rid of the scaling. Run the engine in a container with vinegar? lots of CLR? I suppose the scaling isn't helping heat transfer but I can run the engine ice cold if I pull the hoses off that lead from the heads to the thermostat housing.

My next steps:

1) Replace heads
2) Descale
3) Test Run!
4) Overheat? Pull Thermostats
5) Test Run!
6) No overheat? Research OEM lower temp stats, OEM weaker poppet springs... any other ideas?

 

[HighTrim]

Re: Help! Stumped! 90HP Overheating!

Sounds like you have a water blockage to the port bank. Drop the lower unit , there will be a rubber grommet on top of the impeller housing. Make sure that this is seated correctly and not shoved into the impeller housing restricting water flow, Ive seen this happen many times. Also while the lower unit is down, run some compressed air or the garden hose up the water line, taking out one t stat at a time, letting the air/water exit there. This will ensure that the water line is not clogged. Make sure you remove only 1 t stat as a time to ensure that each passage is clear.

 

[apaulos]

Re: Help! Stumped! 90HP Overheating!

Thanks!

I tried all that when I suspected it was a "not enough water getting to the heads and block" issue. My understanding is that I've got a "not enough water leaving the heads and block" issue. The thermostat housing merges water from both heads in case one of the stats fail. Also the block side of the thermostat housing merges the flow past the stats. When I pull the stat housing again I'll try forcing water from the block to the foot to verify that the out going flow isn't restricted. I also try the rest you suggested if I end up replacing all of the cooling system with OEM parts.

Sounds like you have a water blockage to the port bank. Drop the lower unit , there will be a rubber grommet on top of the impeller housing. Make sure that this is seated correctly and not shoved into the impeller housing restricting water flow, Ive seen this happen many times. Also while the lower unit is down, run some compressed air or the garden hose up the water line, taking out one t stat at a time, letting the air/water exit there. This will ensure that the water line is not clogged. Make sure you remove only 1 t stat as a time to ensure that each passage is clear.

 

[Chinewalker]

Re: Help! Stumped! 90HP Overheating!

You might want to just pull the thermostat hoses off the cylinder heads for a quick run to not how much water comes out. The water shouldn't have any trouble burbling its way down through the belly pan. I did this on my '84 90 to eliminate possible causes for my own overheat issue. Mine turned out to be a bit too much sealant on the 0-ring that seats between the pump cup and the housing causing it to lose its prime at planing speeds...
- Scott

 

[DHPMARINE]

Re: Help! Stumped! 90HP Overheating!

I can't solve this for you,but will try to help.The port cylinders always run 'cooler' than the starboard cylinders.This is because of the way that water flows thru the motor.Probably 10 or 15 degrees.

So it might be that the water can't get out of the port side fast enough.

Maybe pull the therms out,put it back together,and run it awhile.I'm not saying to keep it that way,but running without just might 'flush' out some restrictions.

DHP

 

[Molaker]

Re: Help! Stumped! 90HP Overheating!

When I pulled the heads off, I noticed lots of scaling on both the heads and the water passages in the block. I need to research how to get rid of the scaling. Run the engine in a container with vinegar? lots of CLR? I suppose the scaling isn't helping heat transfer but I can run the engine ice cold if I pull the hoses off that lead from the heads to the thermostat housing.

No mention of the status of the water deflectors when you had the heads off. Were they in place? Mislocation could cause overheating or possibly restrict flow.

 

[apaulos]

Re: Help! Stumped! 90HP Overheating!

Thank you for all the tips.

I'm going to try the descale and pulling the port or both stats out to test.

Anyone have any good procedures for descaling the water passages in the block and heads?

 

[emdsapmgr]

Re: Help! Stumped! 90HP Overheating!

Check the valve body in the thermostat housing. It has two very small holes in it. These frequently plug up. If they plug, heated water can't get to the thermostats to cause them to open. You will get an overheat. Each hole feeds one thermostat-or half of the block.

 

[R.Johnson]

Re: Help! Stumped! 90HP Overheating!

Have you checked the exhaust cover gaskets?

 

[apaulos]

Re: Help! Stumped! 90HP Overheating!

I haven't. What should I check for?

Have you checked the exhaust cover gaskets?

 

[apaulos]

Re: Help! Stumped! 90HP Overheating!

Update:

1) Only found a couple of references to using muriatic/phosphoric acid to remove scaling. Diluted in a barrel with the motor running and recirculating the acid mixture. I found one reference from an 'old tech' that stated only safe real approach is to manually remove the scale. I ended up soaking the heads in 50/50 vinegar and water for a couple of days. I was then able to brush the scale off with a heavy bristle brush. I'm not sure if I'll bother with the scale that is visible in the water jacket of the block.

2) One other thing to verify if you're experiencing an overheat situation: check the orientation of the head gaskets to the block; are the passages in the gasket closes to the outlet or farthest?

 

[ezeke]

Re: Help! Stumped! 90HP Overheating!

Muriatic acid is just another name for industrial strength Hydrochloric acid. It is arguably one of the most dangerous and damaging products you can use. It etches just about anything that it touches, especially copper water tubes. In any application it is important to completely neutralize the acid after use.

 

[gregr1971]

Re: Help! Stumped! 90HP Overheating!

i had the exact same problem with my 115 johnson, i found that when i removed the port side head "cover", not the head , just the cover that has 400 bolts holding it on, the cooling pasages on the head here completely clogged up with the scale. get a torch and heat around all of them bolts!!!
bet that you will find your problem there. i have an extra set of heads for that engine you have if you need.

 

[1730V]

Re: Help! Stumped! 90HP Overheating!

"Check the valve body in the thermostat housing. It has two very small holes in it. These frequently plug up. If they plug, heated water can't get to the thermostats to cause them to open. You will get an overheat. Each hole feeds one thermostat-or half of the block."

I have seen that. I had an '84' 90 HP that overheated the starboard head all the time. That was the issue.

Also, as "gregr" mentioned, have you had the head "covers" off. My current 50 was blocked up in there. I removed the cover to change the stat on that one and I couldn't believe what was in there. Mine was a sltwater engine though.

 

[apaulos]

Re: Help! Stumped! 90HP Overheating!

Update...

1) After manually descaling the heads, did up the water jacket gaskets and got the heads back on with a set of fresh head gaskets.

2) Disassembled thermostat assy. Cooked the thermo to verify proper operation. Since nothing was wrong with the stats, I decided to cut one inch off the poppet relief valve springs. On the muffs at idle the reduced springs don't allow any water to pass. Water only flows when the stats open.

3) Went for a 35 mile WOT cruise of Tampa Bay... NO OVERHEAT.

I'm glad it ain't overheating but wish I had gone with a proper troubleshooting procedure. Either the descaling resolved the overheat issue or the shorten springs are allowing more water to pass at on plane throttle settings. Using a digital oven thermometer with remote probe, at idle the heads are running at 145 F and during my WOT run 160 F. Not bad. I think this is right on spec. I tested both of my overheat sensors and they closed at 205 F and reopened at 170 F.


Now for the d'uh... during one of my troubleshooting test run on muffs, I unplugged one of the hoses from the stat housing. I observed water shooting out of the housing from where I had unplugged the house. I assumed that this water was water that was flowing from the other head across the housing but in front of the stats. As it turns out the stats casting that the hoses plug into are divided so the water I observered shooting out must of been coming from the head going into the front stat casting, past the stat for that head, into the back side of the stat housing, out past the other stat then the casting then out the hole for the hose I had unplugged. This shouldn't be!!! unless there is a restriction in the block side of the stats... or further down!!! I'm going to run it for now and carefully watch the operating temps. At some point, I'm going to pull the stats and the lower unit. Then I'll try to run water and compressed air to verify that there is or isn't a blockage!

 

[iwombat]

Re: Help! Stumped! 90HP Overheating!

Muriatic acid is just another name for industrial strength Hydrochloric acid. It is arguably one of the most dangerous and damaging products you can use. It etches just about anything that it touches, especially copper water tubes. In any application it is important to completely neutralize the acid after use.

Adding to that. Hydrocloric acid and aluminum is a classic case of a "runaway reaction". Hydrocloric etches the al-oxide and creates a byproduct that creates even more al-oxide by reacting with the exposed aluminum. The reaction keeps getting even more volatile as it progresses.

I'd go ahead and label that a bad idea.

 

[CharlieB]

Re: Help! Stumped! 90HP Overheating!

Reaction depends on the % acid used.

I regularly used a toilet bowl cleaner called 'The Works' 20% hydrocloric acid, as my first tool in cleaning bottom growth off pontoons. 20% eats the organic growth but does not harm the 'toon. NOTE, pontoon is MILLED, forged and rolled not porous casting. In fact the toon is still stained from the growth and I use an aluminum brightener (higher % Hhydrocloride and % sulfuric) to remove remaining stains, followed by copious amounts of freshwater rinse.

Lime-away, CLR or comparable product in volume to flush a motor (I'd run it for 20 - 30 minutes) followed by a GENEROUS freshwater rinse wouldn't scare me a bit. Where are you going to find 20 + gal of CLR?

I use those same chemicals to clear the alum heater in my coffee-maker, follow by three pots freshwater.