Engine overheating!!

[Mickeypowa]

Hi guys !!

I have a 2002 malibu with a 350 mag mpi 2011.

Since yesterday it is overheating. Before the temperature was stabilized at 160 degres F.

So I withdrew the sea waterpump and changed the impeller (I had one spare part). It was pretty worn out, all the 7 wings were broken. I found all the broken parts in the grill after the hose. So I was thinking I would be ok now!

<a href="https://ibb.co/nmbdG46"><img src="https://i.ibb.co/nmbdG46/20200213-162928.jpg" alt="20200213-162928" border="0"></a>

I made a test and the engine still overheat !!! So I think it wasn t the main problem... What do you think it could be ? What can I test ?

Maybe I should withdraw the thermostat ? ( its always hot here !)

Or maybe the circulating waterpump is bad ?

Thanks

Mickey

Edited February 15, 2020 by Mickeypowa

[formulaben]

Some questions:

• How do you know it is overheating?  Do you have any evidence besides the dash gauge?
• Have you verified the impeller is actually turning?  (Take cover off and crank engine. There have been episodes of new impellers installed and spinning on their own shaft, so defective from the factory but appear to be perfect. I would verify the impeller is turning and also remove and inspect the thermostat.)
• Did you verify the raw water valve is open?  (Perhaps it got closed for an impeller change on water?)
• Does you model have a vent line on the transom?  Some older engines have a vent line; on the transom you’ll see a little metal port about the size of a button. After running the engine and shutting down it will continue to vent water like its peeing for a few minutes. If it isn’t venting water it’s plugged up. There’s a hose that will run to the top of the engine. Take that hose off and blow it out with compressed air.
• Are you running in salt water? 
• Is this open cooling or closed cooling?

Edited February 15, 2020 by formulaben
more info

[ahopkins22LSV]

If all 7 ribs were broken on the old impeller, I’d be looking up stream of the raw waiter pump for the broken pieces. Typically caught at the transmission heat exchanger as there is a screen in the line. If that gets blocked, not enough water will make it to your engine water pump therefore not allowing the engine to cool properly.

[Mickeypowa]

Thanks for your answers !!

- I read the temperature on the smartcraft monitor. I think the sensor is good because the temperature rise gradually. Before it stopped rising at 160 degres F and now it doesn t stop anymore, I stopped the engine at 190°F. But I have no alarm coming from the smartcraft, I don't know why.. maybe a problem there too. When I stop the temperature lowers gradually.

- In order to test the new impeller, I disconnected the hose after the sea waterpump and I have pressure and flow there. When you say take cover off, the mean the cover of the waterpump? I will check the thermostat tomorrow I think.

- it is an open cooling system, the raw water valve is open and I use the boat in salt water !

- I got all the 7 broken ribs by disconnecting the hose after the sea waterpump

- when the boat is on the rack and I connect fresh water, the water coming out the exhaust is not really hot, as if it doesn t go through all the engine !

For the vent line, I am not sure I have to check !

 

 

Edited February 16, 2020 by Mickeypowa

[UWSkier]

pull and test thermostat.

When this happens, are the exhaust risers hot to the touch?

[Sethro]

Did you test the boat in the water, or just on a water supply out of the water?  If the latter, it's possible you just didn't raise the rpms enough to get everything primed and flowing again.

[Mickeypowa]

I tested both on water and with the water hose. But I do the tests with water hose most of the time..

What do you mean by everything primed?? I dont understand that word !

Today I withdrew the thermostat housing, but it seems I have no thermostat, the plate has been broken maybe to be opened at everytime ?

Here are the photos and a video when the engine is working...

So what do you think, I am a bit lost, I dont know what to check now... the circulating water pump by withdrawing the cap on the top of it ?

Edited February 18, 2020 by Mickeypowa

[formulaben]

If the boat is on the water (lake/ocean) then it typically doesn't have an issue getting primed, but on a fake-a-lake it is possible that water doesn't get to the impeller and after running for a bit both the impeller and the engine will overheat.  I'd wager that with the hose it isn't priming UNLESS you're using a proper flush valve that has the hose connect directly to a water intake...is that what you have?

 

[Mickeypowa]

Yes I have a hose with a plug like for the garden.

Here is a video of today, I disconnected the hose from the thermostat housing, and we can see the water flow...

I dont understand, the water go through the engine then to the thermostat and then through the circulating pump then again the engine ?

[justgary]

I can see the thermostat in your second image (the housing in your hand).

Maybe back flush the block, check the circulating pump impeller, and get a new 160*F thermostat. 

[jmack]

The thermostat is there, but it's been pushed up into the housing, probably restricting proper water flow. Looks like the outside edge of it corroded away and let it get sucked up into the housing. You'll need to pull that one out and replace it. The new thermostat should sit in the recessed groove of the manifold.

[JasonK]

When the engine is cold, the thermostat stays closed, which keeps the water that's already in the engine block to stay (and is being circulated by the engine water pump). During this time, the water being circulated by the raw water pump, only goes thru the exhaust to keep them cool.

Once the temperature of the block rises, the thermostat opens and lets water circulate thru the whole engine.

If the boat temp rises during high idle or when running above idle, and returns to normal temp afterwards, that's a sign that you didn't remove all of the old impeller pieces and they block the water flow. High flow means more suction, and the pieces get sucked into the transmission cooler screen.

[jmack]

6 hours ago, JasonK said:

When the engine is cold, the thermostat stays closed, which keeps the water that's already in the engine block to stay (and is being circulated by the engine water pump). During this time, the water being circulated by the raw water pump, only goes thru the exhaust to keep them cool.

Once the temperature of the block rises, the thermostat opens and lets water circulate thru the whole engine.

If the boat temp rises during high idle or when running above idle, and returns to normal temp afterwards, that's a sign that you didn't remove all of the old impeller pieces and they block the water flow. High flow means more suction, and the pieces get sucked into the transmission cooler screen.

Look at the pics of the thermostat and read my post above. I really think the thermostat itself is out of place and restricting water flow.

[JasonK]

It's ok to run the boat without a thermostat too. Remove it and run the boat to test the temperature reaction.

[Rednucleus]

Definitely need a new stat!

[justgary]

1 hour ago, jmack said:

Look at the pics of the thermostat and read my post above. I really think the thermostat itself is out of place and restricting water flow.

I fully agree.

[UWSkier]

2 hours ago, jmack said:

Look at the pics of the thermostat and read my post above. I really think the thermostat itself is out of place and restricting water flow.

Yep.  Thermostat corroded away and got stuck.  Nailed it.

[Bozboat]

I would have sold my boat or gone broke years ago without this forum. awesome 

 

Edited February 20, 2020 by Bozboat

[Mickeypowa]

Hello guys!!

Thanks to everybody for your help!

So today I removed the thermostat.

In fact I think its place is in the housing because I found this picture :

 

Then made the engine run a 2000 rpm for maybe 10 minutes, it warmed slowly but finally it keeps on overheating : it doesnt stop at 160f, it continues rising temperature,I stopped at 180f.

I removed the circulating pump but I dont know how to test it to know if its bad ?

I can turn it really easily compared to the sea waterpump. Is it normal?

Another thing strange :

the water coming out at the rear of the boat was becoming warm at the beginning, but after when the engine was rising above 160F it was almost cold at the rear.

if you have any ideas what to check?

thanks!

mickey

 

Edited February 20, 2020 by Mickeypowa

[Bozboat]

Did you replace the thermostat?  The only way the exhaust water would be getting cooler would be if the thermostat closed, (water bypasses the block)

circ pump usually doesn’t go bad, but they are not expensive and since you have spent the labor to remove it,  replace it with a new one. Get the marine version with the bronze impeller.

[Mickeypowa]

No I let the housing without thermostat to test. I go to the US at the end of the week so I will buy everything there.

I made a test again after puting back in place circ pump.

This time the water is hot both sides at rear of the boat.

The temperature rise really slowly I have to put high rpm to make it get hot.

But when I put high rpm (3000 rpm for 15 minutes maybe), I go over 160F and I am forced to slow down.

But maybe it is because there is not enough water coming from the hose...? I will test in the sea tomorrow!!

 

Edited February 20, 2020 by Mickeypowa

[Sethro]

It's really difficult to tell in the video, but it didn't look like much water coming out of the port side exhaust outlet.  I once had an issue with overheating with my 1988 Supra, and I went through every component it could be to no avail.  Eventually, I figured it out by standing on the dock and watching the boat take off and very little water was coming out of one of the exhaust ports.  Turned out the exhaust hose had collapsed inside (no evidence of collapse outside) causing a restriction and subsequent overheating.

[Mickeypowa]

Yes you are right, there is less water coming out of the port side, and this water is hotter.

 I was thinking it is because the waterpump is located on the other side.

But maybe there is a restriction somewhere, I test the boat tomorrow! 

Thanks

[Michigan boarder]

Has the boat always been ran in salt water?  There could be corrosion in the block or manifolds that restrict the flow.

[Mickeypowa]

Hi guys !!

Thanks to all for your help, now without thermostat the boat doesnt go over 110 degre farenheit when I run on the sea !! I gonna change with a new one !! Thanks a lot again

Mickey