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Overheating After Impeller/Stat Replacement

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ljsweeney

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I've got an '88 Ebbtide with a 5.0L (Chevy) engine mated to a Cobra outdrive. Earlier this year, I lightly toasted the upper unit due to a bad lube fill (yes, I know). I replaced the upper unit, and since then I have been fighting overheating issues.

After the upper was replaced, the temp would spike very high - about 220*, but it then would immediately drop down to 180* to 190*. That still seemed too high, but it seemed manageable.

I decided to address the temp issues this weekend. I replaced the raw water impeller in the upper, replaced the seals at either end of the water tube between the upper and lower units, and installed a new 160* thermostat. Of course, all new gaskets were used and were properly sealed. After the work was complete, I ran it on muffs long enough to reach operating temp, which stabilized at about 163*.

While I thought that might fix the mild overheating issues I was fighting, now things are actually worse. The temp spikes high (240*) after a small amount of use, and it does not go back down. I had to anchor off for a while to get the temp to normalize, and then the engine would not start. I'm guessing this was due to heat soak causing internal engine components to expand.

After things cooled down (<140*), I was able to start the engine while I was still in the river. I let it idle for a few minutes, and the temp slowly climbed to normal operating temp (165*). It then slowly climbed to 180*, after which the temp gauge needle jumped dramatically towards another overheat. I killed the motor and came in to call it a night and type this out.

While it's still in the water, I'm gonna run it with the inlet hose disconnected from the stat housing to check the flow. I'm guessing that the water flow will be substandard.

My question is this: assuming that the flow of cooling water is compromised, what do I check next? With a new impeller and stat, I thought I was on the correct path. Is there something else in the lower unit that I should be investigating? What am I missing here?

I'm at a bit of a loss here, so I'll entertain any suggestions. Thanks in advance!
 
Actually there is a thru hull nipple that the hose comes in thru the transom on the outside might be clogged up.

You can backflush that hose and see what comes out of it .

If you have no water coming into the boat.
 
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***UPDATE***

I tested the raw water flow to the 'stat housing with the boat fully in the river, and there was but a trickle. The throttle had to be goosed just to get anything. Given that the temp held steady while on muffs, I would have to guess that there is not an obstruction, but rather there is something wrong with the new impeller that I installed, or I installed it incorrectly.

My questions are now these: What else should I be looking at besides the impeller? I know that the water is pulled up through the screens on either side of the lower unit, but is there any kind of mechanical pump or mechanism in the lower unit that assists the water draw, or does the impeller do all the work?

At the very least, I know I have to pull the boat and work on the impeller - I'm just wondering what other surprises await me. Again, any advise or suggestions are greatly appreciated.
 
chiefalen said:
Actually there is a thru hull nipple that the hose comes in thru the transom on the outside might be clogged up.

You can backflush that hose and see what comes out of it .

If you have no water coming into the boat.
Click to expand...

Thanks for the reply, Chief. I plan on backflushing the raw water input hose that connects to the 'stat housing once I pull 'er out of water. That should be tomorrow or Wednesday at the latest. I will post up the results here.

Anything else I should be looking at?
 
capnlazy said:
Make sure the pump housing isn't warped or excessively worn.
Click to expand...

Pardon my ignorance, but are you talking about the round housing behind the impeller? If so, how do I check for wear - do I have to pull it out to do so, and is there a seal or gasket kit I would need to reinstall it?

Sorry for all the questions, but I'm desperate to resolve this issue by Labor Day. Thanks!
 
The hose kinked on the inside of the transom at the fitting that goes thru the hull ?

With the drive submerged and your not pulling water to the t-stat means it has to be on the outside of the transom.

Ether you didn't install the impeller correctly, or the hose or pipe leading to the thru hull fitting is clogged.

That's why i said backflush it. You could do it with the drive removed.

You can do it with regulated compressed air.

I hit my friend in the face with a ant's nest once with air from me putting air to the hose and his face was in the way.
 
chiefalen said:
The hose kinked on the inside of the transom at the fitting that goes thru the hull ?

With the drive submerged and your not pulling water to the t-stat means it has to be on the outside of the transom.

Ether you didn't install the impeller correctly, or the hose or pipe leading to the thru hull fitting is clogged.

That's why i said backflush it. You could do it with the drive removed.

You can do it with regulated compressed air.

I hit my friend in the face with a ant's nest once with air from me putting air to the hose and his face was in the way.
Click to expand...

Thanks for that. Yes, I plan on backflushing as soon as I get her pulled. What is the max air pressure I should use for that - I don't want to break anything. I will also be checking the hose between the transom and the PS cooler for kinks - I know that the hose from the PS cooler to the 'stat housing is good.

Also, it is entirely possible that I installed the impeller incorrectly. I did follow the instructions outlined in my OMC service manual - but I wouldn't put screwing it up past me. I know the obvious things to check - does the impeller rotate; is the gasket out of the groove - but what else should I look for to see if I did it right? That stainless backing plate doesn't have a specific side that should be facing the impeller, does it?
 
Don't open the drive yet, put air maybe 15-20 pounds to it.

The hose that comes in from the transom the raw water hose goes where first ?

You pulled it off that first stop and started the motor with the drive submerged and got a tickle then what i posted so far before holds true.
 
chiefalen said:
Don't open the drive yet, put air maybe 15-20 pounds to it.

The hose that comes in from the transom the raw water hose goes where first ?

You pulled it off that first stop and started the motor with the drive submerged and got a tickle then what i posted so far before holds true.
Click to expand...

I tested by pulling the water feed hose from the 'stat housing and starting the engine. I got just a trickle of water.

After running that test, I realized that the power steering cooler is the first inline device on that water path, but did not have time to pull that hose too. I mean to perform the same test after pulling the water feed hose from the front of the PS cooler. The way I figure it, if I get good water flow with the second test, then I have a blockage in the PS cooler. If I still have a poor water flow, I have either a blockage in the transom or the outdrive, or the impeller is bad and/or installed wrong.

I also plan on running a clear hose 'bubble test' tonight to see if I'm fighting an air gap in the cooling system.

Hopefully, I'll have some cogent information I can report here later today.
 
Well, now I'm annoyed.

I pulled the hose from the through-transom water feed tube, connected a length of hose to it, and had my wife start the boat. Again - no flow.

So there is either a blockage in the water path in the OD, or the impeller was not installed correctly.

Has anyone ever heard of/seen the water intake screen in the lower unit being so clogged with crap that the engine overheats?

Also, when I removed the old impeller, I noticed that water was standing in the water path on the left side. The left side water path was also filthy and scummy, while the right path was clean and clear of standing water. I take it the dirty water path on the left is due to a compromised flow of water through the OD. I'm assuming that a blockage would be the cause - but where?

I'm very close to giving up and taking 'er in to the shop.
 
You mean a shop that works on omc. A guy that actually knows the drive is far more hard to find then you think.

See omc is out of bus. for a long long time.
 
You have to see if the nipple that goes thru the hull from the drive on the outside is clogged.

We will go from there.

We all here know your setup so please keeping asking and we will keep replying.
 
***Update - Issue Resolved!***

After testing for blockages and finding none, I reluctantly took her in to the shop. It made me feel slightly better when they told me they were just as vexed by the overheating as I was.

They finally ended up replacing the seals in the lower unit. They could not pinpoint which seal went bad, but the end result is that she now runs cool like she's supposed to.

Thanks again for all the suggestions and help on this issue.
 
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