Diagnosing Cooling Problem

[goclmbmnt]

I have had an extremely hard time diagnosing a cooling problem over the past few weeks. Thank you to whoever (I think it was Don) that posted the cooling diagnostic manual. That has been a huge help. Here is what I know:

• I have a good impeller and brand new belt. I?m not convinced I have the belt tight enough, but I?m not sure how the engineers intended for one to tighten it. There is not a place to leverage it or a good way to grab it. It?s fairly tight, but I?d like it a little tighter. No belt squeak though.
• There is not a leak in my hose from the sea water pump back to the power steering cooler and the PS cooler is clear of debris or blockage.
• I have flushed a ton of water back down the hose that connects to the PS cooler to the lower unit. No debris, mud or anything else came out.
• I checked the lower unit clean out (next to the shift linkage) and it was clear.
• I taped the inlets on the lower unit shut and filled it with water from the hose that connects to the PS cooler. From there I get a leak in the lower unit. I get the same leak if I put muffs and the garden hose on it. It comes out from under the "anode" (I think that's what it's called, the metal piece that is designed to corrode first). I took that off to see what was underneath and water seems to fill the lower unit and come out from there. (I should have taken a picture, but didn?t think to last night? can do so tonight it someone needs further clarification.)

In an effort to isolate items, I found a large tub and lowered the out drive into it. I didn?t want pressure from the garden hose to influence performance. It isn?t quite tall enough to flood the area under the anode so I turned on the hose and put it in there to fill that with water. I removed the outflow hose of the sea water pump where it connects to the thermostat housing and back filled it with water. When I started it with this setup, I got air bubbles coming out of the sea water pump, so I definitely have an air leak somewhere, BUT WHERE?!?!?!?

My questions:

1. Possibly an air leak in the sea water pump itself?
2. Is there another place air could be entering the system?
3. Why is there an apparent leak in the lower unit? That doesn?t seem good, but I?m a little terrified about dropping the lower unit on my own.

I will be forever indebted to anyone that provide any hints, guidance, advice or direction. Heck, I?d even take jokes at this point?

 

[Don S]

Re: Diagnosing Cooling Problem

What are we working on?

 

[Howard Sterndrive]

Re: Diagnosing Cooling Problem

I found a large tub and lowered the out drive into it. I didn’t want pressure from the garden hose to influence performance. It isn’t quite tall enough to flood the area under the anode so I turned on the hose and put it in there to fill that with water.

tubs don't work. This is how deep the outdrive should be at start-up - your tub can't make this scenario.

 

[Howard Sterndrive]

Re: Diagnosing Cooling Problem

[*]I taped the inlets on the lower unit shut and filled it with water from the hose that connects to the PS cooler. From there I get a leak in the lower unit. I get the same leak if I put muffs and the garden hose on it. It comes out from under the "anode" (I think that's what it's called, the metal piece that is designed to corrode first). I took that off to see what was underneath and water seems to fill the lower unit and come out from there.

it should leak out like that- there are vent holes that help prime the impeller when the drive is first submerged so air isn't locked in

 

[goclmbmnt]

Re: Diagnosing Cooling Problem

it should leak out like that- there are vent holes that help prime the impeller when the drive is first submerged so air isn't locked in

Awesome... thanks for clarifying.

Sorry Don... I forgot the most important part. 1994 OMC 5.0. Model# 502ACPMDA

 

[Don S]

Re: Diagnosing Cooling Problem

Be careful, you have an SX drive, Howard is showing you a stringer drive. Two completely different drives. In the tub, the water just needs to be above the intake ports on the side of the lower unit.

 

[ljsweeney]

Re: Diagnosing Cooling Problem

Personally, I'd like to hear some background on this issue. To wit, what predicated the overheat condition? How long have you had the boat, and if not for long, do you know its service history?

Now, just a few generic items vis-a-vie water flow testing:

1) As you now know, using the muffs or a tub of water (never do this) will not help you narrow down the issue. You will need to splash the boat to properly test for water flow.

2)Test by using a piece of clear hose connected to the main water feed hose coming into the t-stat housing. You should see no bubbles, and the column of water (when pointing straight up) should be about 3" to 4" high.

Finally, if you do not have a factory OMC service manual, get one. I found mine on eBay, and it is invaluable. You may need to pull the outdrive to resolve this issue, and having the factory manual is the difference between "I fixed it myself" and "&%@*#$!!!"

Please let us know what your testing shows you.

Good luck.

 

[goclmbmnt]

Re: Diagnosing Cooling Problem

Be careful, you have an SX drive, Howard is showing you a stringer drive. Two completely different drives. In the tub, the water just needs to be above the intake ports on the side of the lower unit.

Thanks for clarifying. I've submersed the intake ports in the tub and get water coming out from under the anode. Is that normal like Howard mentions?

 

[goclmbmnt]

Re: Diagnosing Cooling Problem

LJWeeney -
- I've owned the boat for 10 years and have kept good records.
- It seems there isn't a consensus if a tub works or not. Any definitive reasons why or why not?
- As I mention in my post, I know I have air entering the line somewhere. I have the main feed out of the sea water pump blowing bubbles, not water.

 

[Howard Sterndrive]

Re: Diagnosing Cooling Problem

oops I shoulda waited for an answer to the "whatcha workin' on"

Most impellers do push better than they pull though. You still might be hunting a ghost by taping up grates and pouring water in... leaks along the suction side are of little concern if they're below water.

An engine mounted pump is definitely a different case than an earlier Cobra or other drive with pump in it.

I'm with ljsweeney on the manual.
What's the real problem?
Is the engine overheating at idle? under load on plane?

 

[goclmbmnt]

Re: Diagnosing Cooling Problem

What's the real problem?
Is the engine overheating at idle? under load on plane?

The real problem was overheating at idle. Bring up the RPMs and the temperature drops. To me, it sure points to a weak pump, either sea water or circulating, so was trying to diagnosis.

 

[ljsweeney]

Re: Diagnosing Cooling Problem

LJWeeney -
- I've owned the boat for 10 years and have kept good records.
- It seems there isn't a consensus if a tub works or not. Any definitive reasons why or why not?
- As I mention in my post, I know I have air entering the line somewhere. I have the main feed out of the sea water pump blowing bubbles, not water.

I'm going to assume that leaving the 's' out on my screen name was an accident...

Personally, I'm not a fan of using a tub, because I don't trust the results. My op manual states that I should never run the engine until the outdrive is completely submerged, and I believe it (but I do have a Cobra). Do as you see fit.

If you are definitely getting air bubbles at the stat housing, you have an air gap somewhere (you knew that, though). The first place I would check (based on my experiences) would be the water tube that runs between the upper and lower units. It has seals on both ends, and they do perish with age. The water tube itself should be examined for corrosion, especially if used in salt water.

Unfortunately, if your SX is anything like a Cobra, you will need to separate the upper and lower to inspect the water tube and its seals, and to do that, you will need to pull the drive.

Good luck.

 

[Don S]

Re: Diagnosing Cooling Problem

The Cobra's had a a pump on the back of the drive, the SX doesn't so running in a tub is fine as long as the intakes are covered. The system is designed for suction through the ports.
Having said that, put a clear hose on the intake side of the pump and run it either in the water or a tub with the water above the vents. Do you see air bubbles there? If not, your pump is probably shot. Worn out and possibly sucking air from the shaft seal or cover.

Water around the anode on the front of the drive is not a problem.

 

[Nivekt]

Re: Diagnosing Cooling Problem

Forgive me if this is a stupid question, but are you certain it is actually overheating? Perhaps you have a bad temp sender. Have you measured the temperature of the temp. sender with an IR thermometer to make certain it is matching what your gauge is showing?

 

[goclmbmnt]

Re: Diagnosing Cooling Problem

Thanks for all of the advice... After more thought, I decided it wasn't worth potentially "chasing a ghost" so I dunked the back end in the lake. Turns out I got decent flow from the water pump. It wasn't drawing in air like I thought, which I was thrilled with. But, are there are any rules of thumb on how much water should be pushed out of the water pump at idle? Kind of a rough measurement, but I was getting about 3 gallons a min (I filled a 1 gallon pitcher in about 18-20 seconds). I heard somewhere it should be more like 2 gallons in 15 seconds, or 8 gallons a minute. Any thoughts?

Nivekt - No I haven't confirmed, but that's a good thought. I always have assumed it was working right, but you know what they say when you assume... I've seen diagrams out there with temperature readings on different places, but anyone have one for my engine, or something similar? Or should the temperatures be about the same? 1994 5.0 OMC 502ACPMDA

ljSweeney - My apologies... :facepalm:

 

[Nivekt]

Re: Diagnosing Cooling Problem

Thanks for all of the advice... After more thought, I decided it wasn't worth potentially "chasing a ghost" so I dunked the back end in the lake. Turns out I got decent flow from the water pump. It wasn't drawing in air like I thought, which I was thrilled with. But, are there are any rules of thumb on how much water should be pushed out of the water pump at idle? Kind of a rough measurement, but I was getting about 3 gallons a min (I filled a 1 gallon pitcher in about 18-20 seconds). I heard somewhere it should be more like 2 gallons in 15 seconds, or 8 gallons a minute. Any thoughts?

Nivekt - No I haven't confirmed, but that's a good thought. I always have assumed it was working right, but you know what they say when you assume... I've seen diagrams out there with temperature readings on different places, but anyone have one for my engine, or something similar? Or should the temperatures be about the same? 1994 5.0 OMC 502ACPMDA

ljSweeney - My apologies... :facepalm:

Your original owners manual should have some information about the operating temperature. I know that with my 5.7 V8 normal idle operating temp is around 165. When I cruise around a lot it will get up to 170-175. My manual states that 180 is considered overheating.