Overheating today :(

[irideflatland]

1972 Crestliner
120 HP Mercruiser I/O

Bought it earlier this month, no problems with overheating before. Actually when I took it to the boat shop a couple weeks ago they replaced the thermostat because the engine wasn't getting warm enough.
Supposedly the water pump was replaced last season after somebody ran it dry without muffs.

Sooo today it started overheating. We had been wakeboarding for about 3-4 hours, and we were headed back. I smelled something like burning rubber and noticed the motor was making a ticking noise. (If you've ever run your car low on oil and you hear the lifter tick, it sounded like that). Backed off on it, and it cooled down within minutes. Then ran it at 3500rpms and it overheated within a few more minutes again.

So could it just be the oil needs to be changed? The guy I bought it from said he never changed the oil last year. Could this make it overheat at higher RPMs?

Or we did get a little stuck on a sandbar today, but I've done that a couple times before and it never overheated after. Could that have ruined the water pump with the sand or something?

I'm hoping it's the oil so I can fix it quick and take it out tomorrow again

 

[Juniinc]

Re: Overheating today

probably ruined the impeller.

 

[irideflatland]

Re: Overheating today

If it is the impeller, is that an easy fix? Or how much would a shop charge roughly?

 

[irideflatland]

Re: Overheating today

Impeller was good, took the lower unit off and brought it in to the shop. They sold me a water pump kit, so I replaced the upper housing, lower plate, and the 2 gaskets that go around the plate. I replaced the impeller too but kept the old one because nothing is wrong with it.

Anyways, just took it out and it still overheats. Seems to do alright at 35k but when I bring it up to 40k the temp goes red pretty quick. Idling doesn't seem to make it overheat either.
Could the thermostat be stuck open? The shop just replaced it a couple weeks ago because it wasn't letting the motor get warm enough.

EDIT: I meant stuck shut, not stuck open

 

[irideflatland]

Re: Overheating today

Took out the thermostat and it doesn't overheat
Weird because the shop just replaced the thermostat a couple weeks ago.

I drove it for probably 45 minutes at 4000 RPMs, and it did get very close to the red temp zone but it stayed in the green. So I'm thinking I should just leave the thermostat out...

 

[cedarjunki]

Re: Overheating today

test the thermostat or just buy a new one....
and if your still running that thing on however long old oil your asking for problems there too. one of the first things you should have done was change the oil!

 

[irideflatland]

Re: Overheating today

Just got back from the shop and they gave me a new thermostat for free.

I changed about a quart of oil when I took the lower unit off anyways


I have a feeling it's getting hot because of a lean fuel mixture though. Since it sometimes backfires at 4000-ish RPMs (not today though). I heard that could cause overheating. But I don't have $150 for to buy that timing light thing to check my timing...

 

[bruceb58]

Re: Overheating today

I changed about a quart of oil when I took the lower unit off anyways .

How did you take a quart of oil out of your engine when you took off your drive? Please explain.

 

[bomar76]

Re: Overheating today

I changed about a quart of oil when I took the lower unit off anyways

You really need to understand that there is no connection between the oil in your engine and the lube in the outdrive, other that they are carried around by the same boat.

 

[nola mike]

Re: Overheating today

How did you take a quart of oil out of your engine when you took off your drive? Please explain.

presumably gear lube. different than engine oil, OP--you still need to change that. yeah, overheating can be caused by running lean--if that's your cause, you need to fix it before you do serious engine damage. also can be caused by off timing. though i wouldn't suspect either of these as a first culprit. check your plugs (google "lean engine spark plugs" for pics). you can borrow a timing light for free from autozone et al. or a cheap one is about $20.

 

[bruceb58]

Re: Overheating today

You really need to understand that there is no connection between the oil in your engine and the lube in the outdrive, other that they are carried around by the same boat.

Bomar...that was actually funny!

 

[bruceb58]

Re: Overheating today

I have a feeling it's getting hot because of a lean fuel mixture though. Since it sometimes backfires at 4000-ish RPMs (not today though). I heard that could cause overheating. But I don't have $150 for to buy that timing light thing to check my timing...

The timing of your ignition has nothing to do with a lean mixture.

 

[nola mike]

Re: Overheating today

The timing of your ignition has nothing to do with a lean mixture.

no, but a mis-timed engine could run hot. and yes bomar, that was funny.

 

[irideflatland]

Re: Overheating today

Sorry, I changed the gear lube I guess!

I just took two plugs out and took a pic of one of them. They both look the same: black. Which according to http://www.superstreetonline.com/techarticles/130_0703_reading_spark_plugs/photo_05.html means it's running rich... ?

 

[Don S]

Re: Overheating today

First thing I see is the wrong spark plug. You shouldn't have long reach plugs in that engine.

Bet those blue threads on the spark plug were red in the engine and was firing the fuel on intake.

 

[irideflatland]

Re: Overheating today

First thing I see is the wrong spark plug. You shouldn't have long reach plugs in that engine.

Bet those blue threads on the spark plug were red in the engine and was firing the fuel on intake.

So you think the spark plugs are causing the lean fuel mixture? Or is it not a lean fuel mixture at all?

Which plugs do you recommend I buy?

 

[Don S]

Re: Overheating today

Lean fuel mixture is only one of MANY causes for overheat and usually the least of the reasons. Have you checked the impeller yet? Even if it was new 6 months or a year ago, it only take one plastic bag in the water to take out an impeller. Removing the thermostat only means the front cylinder is not overheating. Did you check the rear cylinders?
Timing can cause overheats, and the wrong sprark plugs (as in your case) may be firing before the distributor does.
NGK - BR6ES is what Merc recommends for the spark plug.

 

[irideflatland]

Re: Overheating today

Lean fuel mixture is only one of MANY causes for overheat and usually the least of the reasons. Have you checked the impeller yet? Even if it was new 6 months or a year ago, it only take one plastic bag in the water to take out an impeller. Removing the thermostat only means the front cylinder is not overheating. Did you check the rear cylinders?
Timing can cause overheats, and the wrong sprark plugs (as in your case) may be firing before the distributor does.
NGK - BR6ES is what Merc recommends for the spark plug.

Yeah I got that water pump kit and changed it yesterday, it did nothing. Taking out the thermostat today fixed it. I assumed there was a lean fuel mixture because there will be random backfires sometimes.

I'll get those plugs though and see if it helps. Thanks!

 

[Juniinc]

Re: Overheating today

NGKBR6 I pulled last year,,,a bit worse than yours.
A clogged(all the way) flame arrestor was the reason.
occasional back-fire also has stopped.
Be very careful of information given by Me,,,

 

[bruceb58]

Re: Overheating today

Be very careful of information given by Me,,,

That should go in your signature