Still running hot on muffs. Should I worry?

[jesse_boston]

I'd rather not waste another evening plus gas etc driving to the lake if I can avoid it.

When I bought the boat it seemed to run just fine in the guy's driveway. Heated up to around 175 on muffs and stayed there.

I got it home, dealt with a bunch of other issues, and tested it out in my driveway on the same muffs... it heated up to 180, 190, 200, so i shut it off. Since it was okay on the seller's driveway, I figured that I just didn't have enough flow through the hose.
Headed out to the lake and it ran fine on plane around 170 degrees but as soon as I came off plane the temp alarm went off and the temp gauge climbed and climbed right past 220. I of course immediately shut it down. Everything was too hot to touch. I let it cool for an hour and limped back to the ramp.

I've now put in a new impeller (and complete raw water pump kit) and new manifolds and risers, the old risers were all clogged up with scale and rust and were getting ready to leak. The manifolds looked okay, but it's hard to tell what they look like inside and I couldn't remove any of the plugs to check. Also has a new 160 degree oem thermostat (correct per the Mercruiser parts website)

Testing it on my driveway, it ran well. Same amount of water coming out the back. Heated up to about 185 and stayed there, though the alarm started going off. For 5 or 10 minutes I could put my hands on everything without it hurting, but after about 10 minutes the starboard riser got too hot to leave my hand on it for more than 10 seconds.

Do I just have insufficient flow from my hose? Is there another way I can test this without driving to the lake? Stick the whole butt end of the boat into a big storage bin filled with water or something?

I have not pulled or disassembled the water recirculating pump.

1995 Alpha 1 Gen II 5.7 Thunderbolt IV (0F297698) / Doral 230EX

Thanks!

 

[tpenfield]

I find that my I/O engines generally run cool while on the hose/earmuffs (i.e "in the driveway") because there is no load on the engine. Your temp should be staying much closer to the thermostat temp, rather than climbing to the 180 range.

I'd say you still have a few gremlins running around in your cooling system and it is best to find them now than while out on the water somewhere . . .

There are a bunch of places to look, and my apologies if these have already been checked via some of your other posts.

Risers clogged
Exhaust manifold clogged
Recirculating pump . . . not working well or clogged
Thermostat housing clogged
Oil coolers clogged
Impeller worn or blades broken off
Inlet hose within the bell housing cracked

I'm sure there are more things to check, but that is what I can think of at the moment . . .

 

[jesse_boston]

Has new risers and manifolds, checked the thermostat housing when I put in a new thermostat.
Impeller is new.
Inlet hose checked and not cracked.

Good to know about yours running cooler, guess I have more work to do

I tried sticking the outdrive into a giant rubbermaid bin filled with water. While running, more water came through the idle ports, riser didn't get as hot, but the engine didn't run any cooler. That makes me think circulating pump or thermostat... and since the thermostat is new...

Recirculating pump I guess is next. Oil cooler is a pain to get to. Would be easier to change the starter...

 

[tpenfield]

You can backflush the oil coolers . . . you may not need to access them to see that they are cleaned out.

You would have to disconnect the water inlet hose at the transom and then flush from the water inlet hose at the thermostat housing. See if you get a bunch of impeller fragments or marine life coming out of the disconnected hose at the transom . . .

 

[kenny nunez]

When you had the thermostat housing apart did you check the small by-pass port? Running hot on a hose is one of the symptoms. The port is easy to clear with a drill bit.

 

[jesse_boston]

kenny nunez I thought I had checked it, but at this point I'm rechecking everything, thanks!

tpenfield disconnecting the water inlet hose in front of and behind the engine is sure easier than getting underneath it! I'll give that a try. That should give me an idea of how restricted the flow is too.

 

[jesse_boston]

Now I have it all back apart (well now it is raining so i'm back in the house), I definitely didn't check the small by-pass port, and I also am not even sure where this small by-pass port is!

 

[Lou C]

I would not run it in a tub of water because the water level might not get high enough for the impeller to prime. Use the Merc/Quicksilver round muffs with the metal rod clamp that goes thru the water intake holes and the rubber is more flexible that the rectangular Tempo ones I used to use. Keep at it, you should see it run near the temp of the stat; 160-175. My OMC will run at 160 on the muffs as long as I want to run it. In the water the highest it gets is about 170 after coming off plane.

 

[jesse_boston]

Had another look at the thermostat housing. It's scaly inside, but all the passages are open as far as I can tell. No obvious bypass that could be reached by a drill that I can find yet though.

 

[jesse_boston]

I have both the round mercruiser muffs and the rectangular ones. On the round ones, not enough water was coming through the exhaust ports and it was heating up too fast. Should there be rubber blocking the path for the water from the hose into the muffs on the merc ones?

 

[kenny nunez]

If you cannot see the by-pass port it may be completely blocked. If you do not have the genuine Mercruiser flush out wrap a bungee cord around the gear housing to keep it in place.

 

[Lou C]

I have both the round mercruiser muffs and the rectangular ones. On the round ones, not enough water was coming through the exhaust ports and it was heating up too fast. Should there be rubber blocking the path for the water from the hose into the muffs on the merc ones?

Not sure what you mean here. If you are using the round ones with the rod clamp that goes thru the water intake holes if you get them on good and tight they work great.

 

[Rick Stephens]

I always like to start at the beginning. In the driveway, pull the line off the thermostat housing that is coming in from the transom and oil cooler. Hook up your muffs, turn on the water and fire up your motor. You should be able to fill a 5 gallon pail in less than 30 seconds from that hose.

I would also recommend never run an IO in a bucket of water. Muffs are the only safe way. Almost impossible to get the water pump fully submerged, and that type of pump is vented to the exhaust passageway to self prime when submerged. It cannot produce any suction. None at all. I the pump is not completely submerged you damage the impeller really quickly.

 

[jesse_boston]

I don't think my hose makes over 10 gallons per minute, but I'll give that a try.
Good to know about the pump not making suction.

 

[Rick Stephens]

I don't think my hose makes over 10 gallons per minute, but I'll give that a try.
Good to know about the pump not making suction.

That's about 5 gallons in 30 seconds... this tells you if the plumbing between pump and thermostat housing is clear and working right. It narrows your investigation down. If you have 5 gallons in 30 seconds, then because you already know the risers and manis are good, your conclusion at that point is blockages in the motor water jacket.

 

[jesse_boston]

What I mean is that if I point my garden hose into a bucket, boat is not part of the picture at all, I only get about 2 or 3 gallons in 30 seconds, so there's no way I can get 5 gallons in 30 seconds from the raw water pump, my house just doesn't supply it fast enough.
Maybe I need a bigger hose.

 

[harringtondav]

Below is a scan from my engine manual showing minimum raw water pump output. Output varies depending on your drive's reduction ratio. Most common drives are are around 3.5 quarts in 15 seconds. The test must be made with the boat in the water since garden hose pressure will skew the results.

Start the engine and set the idle at 1000 rpm. Remove the hose from the transom/oil cooler at the thermostat housing per Rick Stephens. Collect the water in a container for 15 seconds. Shut off the engine. 15 seconds will prevent starving and cooking the exhaust flappers and tubes. Measure the volume in the container. The manual states to repeat and take the average of four measurements. If you are over the minimum after one sample, I'd call it good.

If the average volume meets the minimum, your raw water flow is OK, and you need to check downstream for blockages. If the test volume is low, you need to check for leaks or obstructions in the supply line. Your PS cooler may be blocked.

View attachment Pump output_Page_1.jpg

 

[jesse_boston]

Okay, I tried backflushing the inlet hose that runs under the engine. It turns out there is no power steering cooler or oil cooler under there, just a piece of pipe. Nothing but water came out of it and water goes through without any backpressure.

Next I pulled off the water circulation pump and pulled it apart. It is in great shape. New gaskets and it is back together.

I looked at the thermostat and could not find any small bypass holes, perhaps that is for the older style of thermostat housing... if there is one on the flat top (4 hose) housing, and you can describe the location, I'd appreciate it.

Next I tried filling a bucket with water using the hose I had used for the muffs and it took about a minute and a half to get 5 gallons. So, I went to the hardware store and bought a new 5/8" hose, now I'm getting better flow, 5 gallons in about 30 seconds.

I was going to try starting it up, but the deposit dissolving engine flush (h8eraide brand) I ordered a couple weeks back finally arrived while I was working on the circulation pump, so I'm going to fill up the engine with that stuff and let it set for 30-45 minutes... once I can figure out how to open the block drains, that is.

 

[jesse_boston]

Figured out the engine drains, there are two different kinds for the two sides of the engine... starboard with a small knurled thumbscrew, and port with a big wingnut deal. Not a fan of either one... can I replace them with the same type of plastic drain plugs as are in the manifolds?

Power steering cooler is actually present, but power steering hoses bypass it, it is just sitting there doing nothing (and it didn't present any restriction when i forward or back flushed it yesterday).

 

[jesse_boston]

Hmm.
Hmmmmmmm.

So I used the engine flush. What came out was definitely rather gross.

As mentioned above, I also backflushed the power steering cooler, and I removed, inspected, and reinstalled the circulation pump, re-checked the thermostat housing, used a new garden hose with better flow, and generally just touched every part of the cooling system again.

Put it on the quicksilver muffs with the new hose. Started her up. She slowly climbed right up to 183 degrees indicated, and generally just hovered there. Same as a few days ago when I started this thread, though now the risers never got too hot to touch.

So I went into the kitchen and borrowed the infrared thermometer.
Port side riser: 78 degrees
Port side aft elbow: 85 degrees
Starboard side riser: 85 degrees at the front, 97 degrees at the aft end
Starboard side aft elbow: 145 degrees
Thermostat housing closest to the engine: 110 degrees
Thermostat housing right where the water hose to the circulation pump connects: 145 degrees
Outside of the big circulation pump hose: 135 (yes i know, it's rubber so not a super useful measurement)

With the dash indicating 183, shouldn't I find *something* on the engine that is hotter than 145?
What else should i check?
Maybe all this time my temperature gauge or temperature sensor are busted?