5,7 Mercruiser overheats

[Ostsideend]

Hi @ all,
first of all sorry for my "ginglish". I did search a lot around in this (very good) forum, but not finding a hint to my problem. Hopefully you can help me out what i realy appreciate.

5.7 Merc. with roller lifter with Alpha 1 Gen 2 sitting in a Bayliner 2655

Problem:

• Engine overheats starting at 3700-3900rpm very quick.
• Cools down very fast when slowing down.
• In idle (no gear in) it does not overheat even by running at high rpm.
• Without thermostat same thing.
• Right exhaust side gets approx. 10-15 degrees C? hotter than left one.
• When getting hot coolant sprays out of the heatexchanger sudden- and heavily.

New: shortblock, internal water pump, impeller, Edelbrock 1409 and EDE intake manifold, exhaust manifold, spacer.

"Old": "1/2" closed cooling system from seakamp, ignition and the other outside attachments.

Already checked: Z drive, Impeller, heat exchanger for steering oil, seakamp pressure check looses 0,1 bar within 1,1 min, spark plug colour fine, compression cold 10 bar, valve "butterfly's" in exhaust channel OK.

Question. Are there any messages that a (1/2) closed cooling system does not work together with the standard sea waterpump in the Alpha 1 Gen 2 drive?

This is my boat


This is the Seakamp model


this is the "spacer or guide" pipe above the "internal" water pump


exhaust manifold with some spots in the middle?!?


Some ideas?

I know, i better have done the clear hose check last year beeing "in the water". But anything i can check before getting in angain?

Thanks a lot and best regards from Germany
Oliver

 

[Bondo]

Re: 5,7 Mercruiser overheats

Ayuh,....

Drop the Lower Unit,+ Backflush the line feeding the Heatexchanger....
Look for debris from old broken impellers...

Is the Heatexchanger Clean,..??
Did you put the T-Stat back in,..?? If Not, Do so...

 

[84Monaco]

Re: 5,7 Mercruiser overheats

Your english is just fine! Better than a lot of folks who grew up with it...

 

[Ostsideend]

Re: 5,7 Mercruiser overheats

Ayuh,....

Drop the Lower Unit,+ Backflush the line feeding the Heatexchanger....
Look for debris from old broken impellers...

Is the Heatexchanger Clean,..??
Did you put the T-Stat back in,..?? If Not, Do so...

Hi Bond-O,

I disassembled the lower unit, the cooler for steering all the way up to the heat exchanger. There is no dirt or other things beeing found. (exept one O-Ring from the flat sealing surface between upper unit and transum, but mine was still in there)

Unplugging the water inlet hose towards the heat exchanger gives me a high volume of water by running the boat in the lake. (last year)

See inlet side of heat exchanger.


T-Stat ? Whats that?

Thank you
Oliver

 

[Ostsideend]

Re: 5,7 Mercruiser overheats

Your english is just fine! Better than a lot of folks who grew up with it...

Regards
Oliver

 

[Don S]

Re: 5,7 Mercruiser overheats

T-Stat = Thermostat.

 

[Don S]

Re: 5,7 Mercruiser overheats

A couple of things to check, and what year is it?
1. Are you getting the proper timing advance from your distributor?
2. Have you checked the outlets in the exhaust risers to make sure they are open. Make sure the exhaust hoses that attach to the riser are not burned and covering the outlet.

 

[Ostsideend]

Re: 5,7 Mercruiser overheats

T-Stat = Thermostat.

Hi Don S,
thanks. T-Stat is already back in. Took him out for a test only.

Any other possibilities where the problem comes from?
Whant can i check?

I will flush as described before.

Oliver

 

[Ostsideend]

Re: 5,7 Mercruiser overheats

A couple of things to check, and what year is it?
1. Are you getting the proper timing advance from your distributor?
2. Have you checked the outlets in the exhaust risers to make sure they are open. Make sure the exhaust hoses that attach to the riser are not burned and covering the outlet.

The 1st motor was a 5,7 from 1997 flat tappet but now it is an 5,7 shortblock from first mate marine with roller tappets.

Distributor works by changing the rpm...

Yes, see:








OK, i will check again the outlet situation on the riser when the rubber hose is installed.

Thanks
Oliver

 

[Don S]

Re: 5,7 Mercruiser overheats

In your last picture, I was referring to the outlet you have your thumb over. That is where the water comes out.

 

[Ostsideend]

Re: 5,7 Mercruiser overheats

In your last picture, I was referring to the outlet you have your thumb over. That is where the water comes out.

Thanks, i got it. This channel is "free" but i check together with the rubber if there is still enough space to let the water out.

Question:
There are smaller rust spots everywhere. it starts in the Exhaust manifold. The last ride to get the boat out was with 1200rpm for 2 miles. Is this a spray back from the outlet or where does it come from? Is it "normal"?

Oliver

 

[Don S]

Re: 5,7 Mercruiser overheats

Question:
There are smaller rust spots everywhere. it starts in the Exhaust manifold. The last ride to get the boat out was with 1200rpm for 2 miles. Is this a spray back from the outlet or where does it come from? Is it "normal"?

Yes, it's normal. It's called reversion. Due to valve overlap some air is sucked back into the exhaust when running. With a wet exhaust and low rpms, you will usually get some water pulling back into the exhaust. Especially with the newer engines.
Merc recommends that if you have been running at low rpm for an extended period of time that you rev the engne (In neutral) to approximatly 1500 rpm for a few seconds to blow the water out of the exhaust just before shutting off the engine.

 

[Ostsideend]

Re: 5,7 Mercruiser overheats

Thanks Don!

Are there any messages that a (1/2) closed cooling system does not work together with the standard sea waterpump in the Alpha 1 Gen 2 drive?

I heared some guys "bull ****ting" about it, but i can't find something in the net.

Oliver

 

[Don S]

Re: 5,7 Mercruiser overheats

With the half system, there normally isn't a problem with using just the outdrive pump. With a full system there is a lot more heat to deal with because the exhaust manifolds are cooled with antifreeze too.

If you are overheating at that rpm only I would bet you have a restriction in your cooling system lines somewhere between the drive and the engine. 2 very common places is the hose being kinked between the drive and the transom shield.
I have also found that z shaped fitting that goes through the transome sheild is a good place to collect debris. While it may look like plenty of flow at low rpm, it's just not allowing enough flow for the higher rpms.

 

[Ostsideend]

Re: 5,7 Mercruiser overheats

With the half system, there normally isn't a problem with using just the outdrive pump. With a full system there is a lot more heat to deal with because the exhaust manifolds are cooled with antifreeze too.

If you are overheating at that rpm only I would bet you have a restriction in your cooling system lines somewhere between the drive and the engine. 2 very common places is the hose being kinked between the drive and the transom shield.
I have also found that z shaped fitting that goes through the transome sheild is a good place to collect debris. While it may look like plenty of flow at low rpm, it's just not allowing enough flow for the higher rpms.

Thanks Don.
I will again go all the way from the lower unit up to the heat exchanger and check for debris or other restriction. And or try to flush it vise versa. There is a plastic pipe going into the transum. This was replaced by a new on. It had a small deformation. But the effekt did not change. But anyhow. I will double check.

Thanks for your hints and help. I 'll do the job in a couple of hours and let you know by pictures.

Last question (for today )
A defekt cylinder head or gasket is not one of the possibilities?

With best regards
Oliver

 

[Don S]

Re: 5,7 Mercruiser overheats

Last question (for today )
A defekt cylinder head or gasket is not one of the possibilities?

That can be checked by doing a leakdown test on each cylinder. Leave the top of the heat exchanger and look for bubbles.

 

[Ostsideend]

Re: 5,7 Mercruiser overheats

That can be checked by doing a leakdown test on each cylinder. Leave the top of the heat exchanger and look for bubbles.

doing a leakdown test? Is it a compressed air connection via the spark plug thread, by closed valves? will be 6 bar of air pressure sufficient?

Oliver

 

[Don S]

Re: 5,7 Mercruiser overheats

doing a leakdown test? Is it a compressed air connection via the spark plug thread, by closed valves? will be 6 bar of air pressure sufficient?

Basically, you have to get the piston at exactly TDC on the compression stroke (Both Valves closed) then apply air pressure to the cylinder.
6 bar should be plenty of pressure to find the leak since the running compression is probably only half that.

 

[Ostsideend]

Re: 5,7 Mercruiser overheats

Basically, you have to get the piston at exactly TDC on the compression stroke (Both Valves closed) then apply air pressure to the cylinder.
6 bar should be plenty of pressure to find the leak since the running compression is probably only half that.

Thanks Don,
but the compression test i did gave me 10 bars each cylinder just in starter speed. I guess while the engine is running at 3700 oer more it should be even higher than that. Or did i miss you?

For tomorrow i have enough tips and hints to be checked. And i have to prepare an air connection plug for the spark plug thread as well.
Getting tired at 2 in the morning...
Thanks again
Oliver

 

[Don S]

Re: 5,7 Mercruiser overheats

I'm not talking about a compression test. A compression test probably wouldn't show a slight leak from a head gasket or small crack in the head or block, and running compression is lower than cranking compression.
Google "leak down testing" and you will find many articles on how to do it.