Overheating Mercruiser 3.0L

[Lewis1111]

Hey everyone really need some help with this one. I've poured through all the other forums and can't seem to figure this one out. The engine is 2000 M/C 3.0L Ser#L639645.

I am having a overheat issue....The temp gauge will slowly climb to 200 and I can confirm that when checking with temp gun at the t-stat housing. Thinking it was the impeller and since it has not ever been done I decided to put a new kit in. New impeller and hsng as well as all new gaskets. Go to run up again and it displays the exact same as before. It is pumping water well out the t-plate and has good water flow to the t-stat hsng.

Last year the c-pump was leaking so that was replaced as well as the t-stat last year. I even tried another t-stat this past week and still had the same issue. I removed the exhaust riser to check the flapper and that looks good as well I did a compression test and checked spark plugs for water and no signs. Comp was 150 psi across the board. No water in the oil either.

If anyone has any ideas of where to look next that would be greatly appreciated!!

 

[Don S]

Re: Overheating Mercruiser 3.0L

Did you check the water passages in the exhaust elbow? Do you boat in salt water or fresh water?

Does it overheat at idle or only at high speeds?

 

[Lewis1111]

Re: Overheating Mercruiser 3.0L

Hi Don thanks for the quick reply. It seems to overheat at any speeds obviously quicker at higher speeds, but yes it will slowly start to climb when at idle, it does not seem to get as hot, it may only reach 185-190 when at idle.

Yes also had a look at the water passages while the exhaust was off and they looked good. I was just working on it and noticed a small amount of water bubbling out from one of the head bolts on the top of the engine, right next to the valve cover.

I am thinking there may be a small leak there and maybe it is sucking air? Compression was good but I am unable to perform a leak down test at the moment. I may pull the head and see what condition the gasket is in.

Any thoughts?

 

[Don S]

Re: Overheating Mercruiser 3.0L

Was the head ever removed from the engine?

You really need to do a partial leak down test before you pull the head off.

Bring each cylinder up to TDC and pressurize each cylinder using the hose from your compression tester and and air compressor.

Remove the hose between the thermostat housing and exhaust manifold, put a clear hose on the thermostat housing and fill it with water and keep the open end up above the engine.

Check each cylinder at TDC with 75 - 100 psi and see if there are any bubbles coming up into that clear hose. If there is, you know which cylinder to look at.

 

[Lewis1111]

Re: Overheating Mercruiser 3.0L

That's great I will try that ASAP and get back to you with the results!

 

[Lewis1111]

Re: Overheating Mercruiser 3.0L

OK I was able to get my hands on a cylinder leak down tester. My readings are 1: 5% 2. 30% 3: 30% 4. 5% in leakage.

Now I can not seem to pinpoint exactly the leak but I know it is not the coming through the intake or exhaust valves and I do not here it coming through the dipstick which leads me to believe it is the head gasket where the leak is coming from between cylinders 3 and 4.

30% does not seem like that bad of leak on this engine, would this be enough of a leak in the head gasket to cause the overheat? Regardless I may need to replace the gasket just to rule this out.

Thoughts?

 

[Glastron3.0GLP-C]

Re: Overheating Mercruiser 3.0L

I took my 3.0l to my mechanic for a leak down test for a cooling problem issue. The test was better than yours with 5%, 5% 15% and 20%. No bubbles in the clear hose or air leaking anywhere but the mechanic insisted that we need to change the head gasket. I agreed to pay 10 hours labor and I will know soon. Research online shows that over 10% leakage on marine engines need attention.

 

[Lewis1111]

Re: Overheating Mercruiser 3.0L

Thanks for the reply, that is interesting, I should probably be doing the head gasket then,.

 

[Lewis1111]

Re: Overheating Mercruiser 3.0L

Glastron 3.0 GLP-C Have you got your boat back yet with any success.

I just replaced the head gasket and did all the valve adjustments and did not make one slight difference to my cooling issue. If any one has any thoughts I am open to anything at this point.

I am going to perform another leak down test to ensure there were no issues with the install.

 

[Glastron3.0GLP-C]

Re: Overheating Mercruiser 3.0L

My head was warped so it was sent to a machine shop for milling and pressure/vaccum testing. The yard will install it soon. I will let you know if the cooling problem was solved.

 

[Glastron3.0GLP-C]

Re: Overheating Mercruiser 3.0L

Unfortunatelly just after the head gasket replacement the engine overheats at idle and up to 1000 rpms at the water. The shop is still trying to figure it out. It looks like they did a $1500 mis-diagnosis! I will let you know.

 

[dingdongs]

Re: Overheating Mercruiser 3.0L

is the riser to manifold apertures clear as well as gasket installed correctly.sounds as if a restriction is playing havoc.

 

[Lewis1111]

Re: Overheating Mercruiser 3.0L

Are you thinking head gasket installed correctly? Or the manifold gasket? I will remove all today likely and take a look for any blockages.

 

[Lewis1111]

Re: Overheating Mercruiser 3.0L

Had the engine torn down again this week and took the head into a shop in town that specializes in engine heads. They said the head was out .06, so they machined it for me and went through the rest of the head and said everything looked good.

While it was off I went through every water passage in the block and intake/exhaust manifold as well as the exhaust system and flappers inspected. Re-installed everything with new gaskets and torqued, re-set all the valves and new plugs-run up today and not one bit of change!! checking all areas with the IR Gun and doesn't appear to be any major blockage in the system, all readings across the block and head seem consistent, getting pretty frustrated with this, I will probably pull the leg again and inspect everything.

 

[slag]

Re: Overheating Mercruiser 3.0L

Have you tried removing the thermostat completely and seeing if it still overheats? Just to try it out, I wouldn't run it like that regularly.

 

[DXN]

Re: Overheating Mercruiser 3.0L

Just a thought. When I was inspecting my bellows today I noticed the copper water tube has a Hairline crack at the gimbal housing.
Could you be losing cooling water before it gets to the engine?

 

[Lewis1111]

Re: Overheating Mercruiser 3.0L

Update:
I decided to finally try and isolate the issue between the drive unit and the engine. I removed the drive unit and supplied water through the inside of the t-plate to the inlet hose going to the t stat hsng.. NO OVERHEAT

I then supplied water to the outside of the gimbal hsng where the water inlet is and.....NO OVERHEAT. Knowing now my issue is in the drive unit somewhere or possibly a exhaust issue still, I took the drive apart again and inspected everything little thing I could thing-removed the new water pump and checked all hoses and gaskets.

Didn't see anything blatantly obvious but put it all back together very slowly and making sure everything was perfect-re installed the drive and ran up....NO OVERHEAT!!

Not to get far ahead this was all on the garden hose, I will be taking the unit down to the water tmrw and see what happens. Fingers crossed.

Will update status tmrw.

 

[clydey]

Re: Overheating Mercruiser 3.0L

As crazy as this sounds but did you check the passage from the bottom of the outdrive ( the holes are where the muff goes on) and make sure that is clear?Yesterday I pulled mine apart to install a new pump kit and there was a hunk of old impeller down there wedged. With the garden hose you are forcing water and with the pump you are just picking up.Just a thought.

 

[whynson]

Re: Overheating Mercruiser 3.0L

Also just a thought, are you sure the impeller blades are bent the correct way when you installed it? Not trying to offend, just throwing out ideas

 

[DXN]

Re: Overheating Mercruiser 3.0L

I'm really curious how things worked out for you