Author Topic: mercruiser overheat trouble shooting (Read 9481 times)

76bayflite · « **on:** May 11, 2014, 07:53:38 PM »

Hooked up a hose and fired up the boat today. After a few minutes it was running pretty hot. After I turned it off I pulled off the intake hose and crank the engine. Water pumped out pretty steady. Then I pulled out the thermostat, it didn't run too hot at idle but as soon as I gave it some gas it got pretty hot. Any other suggestions? Thanks in advance.

Rich_V174SS · « **Reply #1 on:** May 11, 2014, 08:06:06 PM »

Check the water flow through the exhaust riser. How much is coming out of the engine behind the boat compared to what's going in. A plugged up riser/elbow will cause the engine to overheat. If the flow is ok then the front water circulator on the engine may be shot, pull it off and check the impeller on it.

76bayflite · « **Reply #2 on:** May 11, 2014, 08:11:58 PM »

I pulled one of the brass plugs and water wasn't really flowing out of there like I've seen before. Maybe I should have mentioned that. It did seem like there should have been more water coming out of the hub.

Rich_V174SS · « **Reply #3 on:** May 11, 2014, 08:15:54 PM »

How recent is the water pump in the drive, and is it an OEM Mercury impeller?

My first thoughts in this order would be:

1) Water pump in the drive
2) Riser/Elbow
3) Circulator on the engine

carlsoncvx18 · « **Reply #4 on:** May 11, 2014, 08:19:28 PM »

I chased a overheating issue for quite a while.
As Rich said it ended up being the risers on the exhaust.

Took them off soaked them in a tub of muraic acid, you would not of believe the stuff that came out.

But it did cure my over heating issue.

76bayflite · « **Reply #5 on:** May 11, 2014, 08:42:35 PM »

New impeller last September

Rich_V174SS · « **Reply #6 on:** May 11, 2014, 08:46:35 PM »

Then if you've got good garden hose like flow coming out of the inlet hose when removed from the engine and very little coming out of the engine then something is restricting the flow in between. I would check out that exhaust elbow. I replaced mine a couple years ago because it plugged up while sitting over the winter.

CVX Fever · « **Reply #7 on:** May 12, 2014, 11:05:17 PM »

Why are we talking about outboards on a thread titled " mercruiser overheat trouble shooting"? How about we start are own thread, versus hijacking someone elses. He hasn't even gotten his problem solved yet. Very rude IMHO.

dorelse · « **Reply #8 on:** May 13, 2014, 04:47:50 PM »

Quote from: CVX Fever on May 12, 2014, 11:05:17 PM

Why are we talking about outboards on a thread titled " mercruiser overheat trouble shooting"? How about we start are own thread, versus hijacking someone elses. He hasn't even gotten his problem solved yet. Very rude IMHO.

Good call. New topic created, let's keep this one for helping Sean!

Jerry · « **Reply #9 on:** May 13, 2014, 04:56:10 PM »

My post was about overheating, not just on outboards. I don't think it was out of place.

dorelse · « **Reply #10 on:** May 13, 2014, 05:05:17 PM »

Quote from: Jerry on May 13, 2014, 04:56:10 PM

My post was about overheating, not just on outboards. I don't think it was out of place.

Didn't think it was either Jerry, but was applicable to both, and had an OB pictured, so I moved it with the other thread. Judgement call on my part...not intended as a admonishment in any way.

As I side note, I couldn't get get my OD in that high of bucket...which is also why I moved it.

Jerry · « **Reply #11 on:** May 13, 2014, 05:25:40 PM »

You put the tank in place under the OD before you fill it.

76bayflite · « **Reply #12 on:** May 13, 2014, 06:40:33 PM »

Really didn't bother me, I've got some good ideas from rich and jeff. I'll pick up some acid tomorrow and give that a shot.

Neutron68 · « **Reply #13 on:** May 14, 2014, 10:06:53 AM »

76bayflite, I'm very interested in what you discover!

I'm trying to diagnose (what I think is) the same problem in my 1978 Mercruiser 120.
I got the boat during summer 2013 and the TEMP idiot light was lit at some brightness level during most of a boat cruise (even during a slow, 1500 RPM speed), but the engine was just warm, not terribly hot to the touch.

I started by removing the thermostat. It ran with the light much dimmer, but it was still on during a cruise.
Then, I replaced the thermostat. It ran with the TEMP light on at varying brightnesses during a cruise.
I just installed a temperature gauge in place of the TEMP light, so I'll have a better read on the actual temperature, when I finally get the boat in the water this season.

In the fall, Rich suggested that it could be rusted water channels in the exhaust elbow.
Thus far, I've not removed it to look.
The Mercruiser manual suggests you have to disassemble lots of things (throttle cable, fuel line, and all hoses in the area) to get the elbow off.
Is that true?
see page 591 here http://boatinfo.no/lib/mercruiser/manuals/mercruiser3.html#/590

I'll stay tuned to this thread!
Eric

75starflight · « **Reply #14 on:** May 14, 2014, 10:51:09 AM »

Quote from: Neutron68 on May 14, 2014, 10:06:53 AM

In the fall, Rich suggested that it could be rusted water channels in the exhaust elbow.
Thus far, I've not removed it to look.
The Mercruiser manual suggests you have to disassemble lots of things (throttle cable, fuel line, and all hoses in the area) to get the elbow off.
Is that true?
see page 591 here http://boatinfo.no/lib/mercruiser/manuals/mercruiser3.html#/590

I'll stay tuned to this thread!
Eric

Eric,

to remove the exhaust riser all there is to remove is the four nuts holding it to the manifold. Remove them and loosen the clamps on the exhaust boot below. When I removed the one on my 140 I had to tap it with a hammer to get it to come loose from the gaskets. Other wise it should just lift right off.

dorelse · « **Reply #15 on:** May 14, 2014, 11:24:40 AM »

Quote from: Jerry on May 13, 2014, 05:25:40 PM

You put the tank in place under the OD before you fill it.

Of course you do...com'on Jerry. Topic was started to help Sean with his Mercruiser I/O issues, was quickly taken off topic with an unrelated OB cooling discussion.

I made a call, split the topic. Over & Done.

CVX Fever · « **Reply #16 on:** May 14, 2014, 11:53:47 AM »

Well done Doran!

GCarlover · « **Reply #17 on:** May 14, 2014, 03:41:46 PM »

Doran, thanks for doing a good job splitting the OB from the I/O. Bad call on my part. Thought it was a similar problem. Just wanted a reply from Rich and got it. I don't like to PM the guys if I don't have to.

dorelse · « **Reply #18 on:** May 14, 2014, 05:08:17 PM »

Quote from: GCarlover on May 14, 2014, 03:41:46 PM

Doran, thanks for doing a good job splitting the OB from the I/O. Bad call on my part. Thought it was a similar problem. Just wanted a reply from Rich and got it. I don't like to PM the guys if I don't have to.

Nope, its all good.

Neutron68 · « **Reply #19 on:** May 16, 2014, 11:07:31 AM »

75starflight, if you take pictures of what you find with the exhaust elbow, please share.

If muriatic acid is necessary to clean out rusted-shut water channels, should the elbow be repainted?
What kind of paint?
If a special paint, I'll need to get it in advance, so I have what I need at the cabin.

Eric