More on the Engine Overheating saga

[cterry]

Hello again fellow Mercruiserites.
Here's the latest on the overheating 302 Ford:

Well, I temporarily installed a mechanical temp gauge to ascertain the real temperature and it's definitely running hot. I ran the engine up to about 2500RPM and it got up to 180 degrees pretty fast. I ran it back down to 1000 RPM and let it cool down to about 140.

I pulled off some of the water lines and I didn't see anything that looked funny. Stat housing and exhaust elbow inlets look good so I haven't pulled off the elbows yet.

When I look at the stern drive water outlets, it looks like plenty of water is getting out??? I did check the pressurization of the hoses by pushing down on them while running at 2500 RPM) and they didn't seem that well pressurized to me as it was easy to push them in. However, I'm not sure how much pressure I should see there.

I can also feel the water "pulsing" through the lines and wonder if that indicates a problem. I am wondering if my best bet is to replace the circulating pump on the engine.

Any additional suggestions?

Much appreciated! Chuck.

[Willallison]

On my 5.7L mercruiser, the owners manual gives the flow rates for the various water pumps. The manual recomends checking this flow after replacing the pump / impeller. It's a fairly straight forward procedure. Run the engine at a constant 1000rpm, remove the appropriate hose and time how long it takes to fill a bucket of known volume.
From experience, I can tell you this is a rather wet experience - there's lots of water there - or at least there should be!
From an earlier post, you mentioned replacing the raw water pump in the leg (I think). Is there a 2nd, belt driven pump up near the front of the engine (in addition to the circulating pump)?
The pulsing you mentioned sounds rather ominous - I'd check the flow rate from this pump 1st. Also if you have a mechanics stethascope take a listen to the pump with that - you'd be amazed at the noises you can pick up through one of these.

[cterry]

Will. I think checking the flow rate is a great idea and hopefully one of my manuals will give the metrics. According to the manual there is not a 3rd pump, but I'm gonna check that too. As for that pulse, ominous is the word that came to my mind too. Omnious as in head gasket. I can only pray it isn't that!
I have taken the day off in the hope of cracking this tomorrow. I'll keep you posted. Thank you so much for you assistance!
Chuck.

[gonzo]

The pressure of the cooling water is very low; not enough to stiffen a hose. The pumps are designed for high flow. Impeller pumps normally pulsate a bit. A heat gun would be the best way to test for the cause of the overheat. However, if you don't have accas to one there are several things to test. Start by the water intake and make sure it is not clogged. Then look at the water tube in the raw water pump that is well connected and the seals are in good condition. Next is the power steering heat exchanger. It is bolted on top of the bell housing. Disconnect the hoses and look for debris and old pieces of impeller. This is a typical cause of overheat at high RPM. Test the thermostat. Put a string or feeler gauge between the outside and the inside round plate while it is cold. Heat water to 150* (one cup for 2 min in a microwave aprox.) , submerge the thermostat and it should open quickly in 3-5 seconds. If everything checks, run the engine at idle. You should be able to touch the risers without getting burned. If one or both are too hot, that is the problem. I assume the hoses are not clogged with rust. Also the bottom of the manifold can get clogged and prevent water from exiting. You can check that by taking the plug at the end of it while you are running the engine; water should flow freely. The circulating pump rarely fails. It only makes the water flow more even.

[cterry]

Thanks much Gonzo for the great information. Armed with this and posts from other Mercuriserites, I definitely have adequate info to crack this.

The thermostat is new. I pulled it yesterday and tested it and all is fine with that. Unfortunately, I was foolish enough to pull the circulation pump which was as you stated, needless. It too was fine, but was a real nusiance and I'm stiff as a board as a result of the contortions required to get at it.

The thing that really bugs me about this is that at idle, there is no indication of an issue and everything is normal. When you get up to about 2000 RPM's is when it starts to get funky.

As you suggested, I am going to check the power steering cooler and then the manifolds if necessary.

Thank you so much Gonzo for your thoughtful reply and well ordered information. Thanks again to everyone who took time to reply. I'll put another post up when I have reached a point where I can say "elementary my dear Mr Watson"!

Regards and happy holiday to everyone.

Chuck.

The circulating pump rarely fails

I think gonzo's advice is excellent, but I should say that rarely doesn't mean never and that's exactly what I had to replace on a 302 ford. Mine would run ok up to about 3000 rpm and after that it would quickly climb to 190 and then I when I slowed down it would cool off again. Replaced the circulating pump and everything was ok. How old is your existing circulating pump?

[cterry]

Hi.
Not really certain of the age of the circulating pump, but suspect it's original, making it about 30 years. However, I did pull it and even drug it to a local Mercruiser dealer who verified what I thought upon inspection. It's a bit rough looking, but there is no end play, it turns freely and the impeller looks fine. I have to say though, that my problem sounds exactly like yours!

I had the boat out today in a small lake and we basically hung out in coves and ran around at 2000RPM or less. Everything was just fine. However, the one time I ran it up to 2500, it started climbing.

Well, I certainly appreciate your reply. I'm not certain what I'll do next, although I'm leaning towards steering pump and/or exhaust manifolds. I sure wish the circulating pump would have been bad because I didn't enjoy removing and reinstalling it very much.

Thanks for the post and have a nice holiday.

Chuck.

[Willallison]

The circulating pump rarely fails.

Have to side with "Guest" on this one. When I bought my boat it was 6 yrs old and had only 150hrs on it. The first weekend out, I noticed a change in the engine note - not temp change or anything just a hollow sort of sound. Upon lifting the lid, I discovered water spraying everywhere - one new circulating pump required......

[cterry]

Circulating pump delima:
Will and Guest have me once again contemplating the C pump.
Can either of you remember the condition of it when you pulled it? Was there end play, noise or did the impeller look odd in some way? Is it possible that the impeller blades become so corroded that it has some really strange impact on efficiency?
I'm not seeing any leaks nor is there any strange noise. None of the things I'd associate with a failed pump.

Replacing the C pump woud be preferable to other things and even though I have already had it off and put it back on, I would gladly pull and replace it if I could be sure that it really is bad.

It's so confusing. One thing for certain, this is a terrific forum and I appreciate all of the replies I am receiving! I'm learning a ton!

Chuck.

Had a similar problem on my mercruiser #1 only had additional heating after a power run (ran hot during run then overheated after run). it turned out to be the discharge pipe from the lower unit water pump. the rubber grommet on the top section was cut allowing the water to discharge directly into the exhaust. looked like there was plenty of flow just wasn't going through the engine first. watch installation of lower unit carefully!

my two cents,
chuck D
Tweety Boat
Elephant Butte, NM

[cterry]

Thanks Chuck D.
Something I did notice when running it with a garden hose feed is that with the drive in gear, a lot of water is squirting out around where the prop meets the gear housing. I have no experience with this so I don't know what's normal, but it sure seems like a lot of water getting out of there. I wish I knew what this means or if it simply means nothing. With winter coming on, I might pull the manifolds and go through that section, but if it was unnecessary effort, I'd rather not. I know I need to replace the driveshaft as I saw scoring when I rebuilt the lower unit water pump.

Any additional thought are appreciated.

Regards, Chuck.

[Willallison]

chuck D
Tweety Boat
Elephant Butte, NM

Tell me that's not really your address!!