mercruiser 5.0 mpi overheats at idle

[achris]

Re: mercruiser 5.0 mpi overheats at idle

.... Clymer manual ....

Great as bog roll!

Did you download the manuals for your engine and drive? In the Adults Only section of this forum...

'O' ring #17 should be tossed in the bin.... Later model driveshafts didn't even have a groove for it. If you put it on (in the groove on the early model shafts) they will hold open the lower seal in the top box and allow water in and the bottom of the upper drive shaft will corrode... Not good!

They was a service bulletin from Merc about it sometime in the late 80's (I think).

The quickest way to get this done is to take your time and get it right the first time...

Chris..........

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

Thanks chris...

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

Update Everybody

Tried engine and watched the temp gauge like a hawk and.... overheated!

So i, patiently, removed the first and easiest part of the engine cooling system. Themostat. Put it in kettle with a temp sensor and heated to 160f (stamped on back).... nothing, 170f... cracked open, 185f.... a bit more 200f and all the way to boiling....failed to open fully.

Hopefully this would explain my problem!

Can i test the engine without the thermostat? I'm still out the water and not going back in for two weeks. It will take 3 to 4 days for one to come and i'm dying to confirm this.

Also is it ok to put engine into fwd and reverse at idle to check i have connected everything back together properly? I've heard you shouldnt do this without a load on the drive?

Last question, finally. How can i test the overheat buzzer/warning system as it didnt activate at 220f!

 

[JustJason]

Re: mercruiser 5.0 mpi overheats at idle

Have a look at the tstat. Throw it in some boiling water and make sure its fully opening.

There's you go, glad you found out.
No you can't (it's not that you can't) but you don't want to run an engine without a thermostat. It's not the best thing in the world for it.

As far as testing the buzzer. Pull the temp switch out, put a multimeter on the stud and the other end on the threads or the base of the sensor/switch. Put the multimeter on resistance/ohms. When cold it should have a high resistance to ground. Put it the sensor in boiling water for a minute. Re-check the resistance, it should have little or no resistance.

 

[achris]

Re: mercruiser 5.0 mpi overheats at idle

...

Can i test the engine without the thermostat? I'm still out the water and not going back in for two weeks. It will take 3 to 4 days for one to come and i'm dying to confirm this.

Just for confirmation, it's ok... but not a good idea to run without it...

Also is it ok to put engine into fwd and reverse at idle to check i have connected everything back together properly? I've heard you shouldnt do this without a load on the drive?

Putting in gear at idle is ok (I do it EVER time I have a leg off), no other way to check you got it right. Just make sure NOBODY is standing near the prop or behind the boat.... If the prop flies off it could hurt someone.. What you shouldn't do is rev the engine...

Last question, finally. How can i test the overheat buzzer/warning system as it didnt activate at 220f!

I've just had a look at some circuits and it looks like you don't have an alarm switch on the temp???? Very strange!!!

Can you post up your engine serial number so I can be sure I'm looking at the right drawing....

Chris........

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

Mcm5.0l mpi
4m4122LTT
Ser ow385827

Alpha1 gen one up to 1991
Ser oc893180*

So if I run without a thermostat it will it just take longer to warm up?

 

[achris]

Re: mercruiser 5.0 mpi overheats at idle

Mcm5.0l mpi
4m4122LTT
Ser ow385827

Alpha1 gen one up to 1991
Ser oc893180*

So if I run without a thermostat it will it just take longer to warm up?

No, it won't warm up at all. And as the ECU determines fuel mixture based on (among other things) engine temperature, you'll be running a constant rich condition, and that really isn't good...

Chris.........

 

[achris]

Re: mercruiser 5.0 mpi overheats at idle

....

Last question, finally. How can i test the overheat buzzer/warning system as it didnt activate at 220f!

There isn't an independent temperature alarm switch. The alarm signal is generated, by the ECU, from the digital temperature sensor. If the ECU determines that the temperature is at 'alarm level', it will sound the alarm....

Do you get the check beeps when you switch the key to ON?

Chris.........

 

[achris]

Re: mercruiser 5.0 mpi overheats at idle

...

Last question, finally. How can i test the overheat buzzer/warning system as it didnt activate at 220f!

Just looked in the ECU diagnostics manual... You could test for alarm function by removing the connector from the digital temperature sensor (has 2 wires, one is yellow and the other black/pink) and bridging the wires with a 50 ohm resistor.... That would simulate a high engine temperature condition.... (if you short it to ground the engine won't start)

Chris.......

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

Changed thermostat and now engine runs at 185f at 600rpm and when revved to 1500rpm goes down to 165f. What should the engine run at?
The aft of the stbd riser is hot and the port cold to Luke warm. The water coming out of the stbd transom sheild is hot and the port cold.
So the thermostat was definatly bad but still have a problem. Going to pull the stbd riser now and have a look.
Any other suggestions? I think I am at least getting there now!

 

[achris]

Re: mercruiser 5.0 mpi overheats at idle

Not unusual for one elbow to run hotter than the other. If fact it's unusual if they run the same temp.... on flushers. That's because without back pressure on the exhaust system the water takes the 'path of least resistance' to exit the engine. It only has to be something as simple as the boat being on a slight (very very slight) angle to one side to determine which way the water will go.

Once you get out on the water, it'll be fine.

Chris.........

 

[Fun Times]

Re: mercruiser 5.0 mpi overheats at idle

Changed thermostat and now engine runs at 185f at 600rpm and when revved to 1500rpm goes down to 165f. What should the engine run at?
The aft of the stbd riser is hot and the port cold to Luke warm. The water coming out of the stbd transom sheild is hot and the port cold.
So the thermostat was definatly bad but still have a problem. Going to pull the stbd riser now and have a look.
Any other suggestions? I think I am at least getting there now!

I have not really read the hole thread yet, But in your testing time you could try setting the idle speed up to 645-650 RPM's like your old carb engine use to idle at to see if the temp will drop down to 163ish degrees.

I say that because of the older style impeller housing you have in your drive may pump a different volume of water then the newer style drives/Impellers, And also the older EFI engines idle down to 600 RPM's and the newer style EFI engines are now set to idle at 540 RPM's and that may have an effect on your temp.

So you might want to confirm your exact idle speed that you have, And also are you doing all this testing while on the lake or in a pool of water of some kind? Or are you using the garden hose???

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

I'm on garden hose. Same results as when in water but I do remember both risers were very hot before taking the boat out. Before at idle it would heat to 200+ now max is 185 but when revved it still goes down. Pretty much same symptoms just not so bad now, thanks to the thermostat.
Riser looks ok, basic look. Will refit when I have the new gaskets and leave it till I'm in the water then.

Cheers guys

 

[Don S]

Re: mercruiser 5.0 mpi overheats at idle

Do not attempt to adjust the idle rpm's, you can't on an MPI engine. The idle rpm is controled by the ECM, not the cable or throttle plate.

 

[NHGuy]

Re: mercruiser 5.0 mpi overheats at idle

Hi,
Butting in here with a confirming remark and observation. My carbuereted '89 5.7 Alpha 1 warped the lower unit water pump last spring and required pump replacement. I am a first time I/O owner and ran it in the yard without water before I discovered this forum.
When complete I got 185 degrees temp idling at the dock and 165 while running above idle speed. I'll be very interested to see if Nauticool can get lower idle speed temps.

I'm also going to recheck when the boat goes back into service this spring. There is a chance it will improve just because of the winterization that was done. This was my first year with this boat and I saw a fair amount of rust bits when I opened & drained the petcocks. My hope is the cooling water may flow better since I probed all the drain points during the winterization.
I'd think Nauticool should not have this issue, his engine was recently changed.
I'll watch this thread closely since I have/had a similar situation.

Sorry If I am off base.

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

There isn't an independent temperature alarm switch. The alarm signal is generated, by the ECU, from the digital temperature sensor. If the ECU determines that the temperature is at 'alarm level', it will sound the alarm....

Do you get the check beeps when you switch the key to ON?

I don't get any beeps when I turn the ignition on. The thermostat housing has two probes screwed into into it. One has the two wires you said and on the other side there is just one cable, i think, a light tan colour. Also at the fwd end port side wiring loom there are spare connectors for accesories but one is black with a ring terminal crimped onto it and not labelled. Should this go to ground?

Will try the 50ohm resistor idea

Thanks

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

"When complete I got 185 degrees temp idling at the dock and 165 while running above idle speed. I'll be very interested to see if Nauticool can get lower idle speed temps"

This is exactly what I am getting running off muffs. Let's see what I get next week when I'm back in.
Will trawl through some other threads to see if anyone else has similar setup and experiences.

 

[achris]

Re: mercruiser 5.0 mpi overheats at idle

I don't get any beeps when I turn the ignition on.

That tells me there is a problem somewhere. My first check would be that the installer connected the piezo buzzer (in behind the instruments).

The thermostat housing has two probes screwed into into it. One has the two wires you said and on the other side there is just one cable, i think, a light tan colour. Also at the fwd end port side wiring loom there are spare connectors for accesories but one is black with a ring terminal crimped onto it and not labelled. Should this go to ground?

The tan wire is the sender wire for your temp gauge. Merc put lots of spare grounds in the harness, used on some models but not others. It's cheaper for them to produce one harness with everything in it than multiple harnesses for each different engine.

Will try the 50ohm resistor idea

Thanks

10 to 1 on you don't get a sound... I still bet the buzzer isn't connected...

Chris.........

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

Can anyone tell me if i have put the stainless gasket plate back on the right way??

http://www.youtube.com/watch?v=SX9OkbgoAGE

The small water jacket cooling hole is at the fwd of the engine and the lip of the exhaust is facing up towards the riser as opposed to the manifold.

I'm pretty sure this is how it came off. The manual is not clear.

Thanks

 

[achris]

Re: mercruiser 5.0 mpi overheats at idle

Yours looks just like this.... Well done....