496 overheating issues!!! Please help

[Dirty Daytona]

2006 496 HO. I’m out in havasu trying to enjoy my weekend. Boat keeps dumping coolant into the bilge. Figured out the coolant was leaking out of the reservoir cap. I’m going to get a new cap in the morning. The boat runs normal temps at idle. The boat also runs normal temps running it at speed, even for 5-10 minutes at a time. After slowing to idle after running at speed the temp keeps spiking way up and then slowly comes back down. Way up like in the 190’s.
If the cap is not actually bad could there be an issue with over pressure in the cooling system?
Why is the boat running in the 160 degree range at idle and mid-full throttle but spiking way up at idle after mid-full throttle runs?
Ideas anyone?

 

[Boat 405]

Impeller. Water is force fed at speed making up for poor performance of impeller which shows itself at idle.

 

[Bigbore500r]

2006 496 HO. I’m out in havasu trying to enjoy my weekend. Boat keeps dumping coolant into the bilge. Figured out the coolant was leaking out of the reservoir cap. I’m going to get a new cap in the morning. The boat runs normal temps at idle. The boat also runs normal temps running it at speed, even for 5-10 minutes at a time. After slowing to idle after running at speed the temp keeps spiking way up and then slowly comes back down. Way up like in the 190’s.
If the cap is not actually bad could there be an issue with over pressure in the cooling system?
Why is the boat running in the 160 degree range at idle and mid-full throttle but spiking way up at idle after mid-full throttle runs?
Ideas anyone?

My boat was doing that, had a loose hose clamp on the raw water supply pump that was causing it to suck air and cavitate. Temp would fluctuate after a hard run, spike and then jump around, eventually cooling off. I don’t have a heat exchanger though, so you have a few more components to check. Hope that helps, make sure all your clamps are tight

 

[Dirty Daytona]

But why only after after mid-full throttle runs? Once it’s cooled back down I can idle around all day long at 165 degrees. It’s only getting hot at idle after running it for a bit.

 

[CobraDave]

Some thoughts. Obvious one is an impeller check. It would makes sense at speed the boat is getting enough water pressure but once at idle it might not be which would cause it to heat up.

Second is I believe 496s want a coolant flush at some point. It might be time. 300 or 500 hours. I can’t remember.

Disclaimer: I’m far from a mechanic.


Sent from my iPhone using Tapatalk

 

[mjc]

Mine did that and had a blown head gasket

 

[Guest06]

2006 496 HO. I’m out in havasu trying to enjoy my weekend. Boat keeps dumping coolant into the bilge. Figured out the coolant was leaking out of the reservoir cap. I’m going to get a new cap in the morning. The boat runs normal temps at idle. The boat also runs normal temps running it at speed, even for 5-10 minutes at a time. After slowing to idle after running at speed the temp keeps spiking way up and then slowly comes back down. Way up like in the 190’s.
If the cap is not actually bad could there be an issue with over pressure in the cooling system?
Why is the boat running in the 160 degree range at idle and mid-full throttle but spiking way up at idle after mid-full throttle runs?
Ideas anyone?

The cap is available at most auto parts stores, it’s for a “2004 Ford Mustang v8, overflow canister”

Did you make sure the impeller is 100% intact? As well remove end caps from heat exchanger to be sure it’s not filled with.... sand, remaining rubber debris from prior impeller, etc?

 

[Guest06]

 

[Bigbore500r]

But why only after after mid-full throttle runs? Once it’s cooled back down I can idle around all day long at 165 degrees. It’s only getting hot at idle after running it for a bit.

The impeller theory -

The engine is generating a lot of heat while running on plane and hard. When you throttle back come off plane / idle it’s possible the water flow is no longer being “force fed” and reduces due to the weak impeller, yet there is still a lot of heat being transferred from the block / heads to the coolant. The inadequate raw water flow from the weak impeller causes the temps to rise for a bit, in till the coolant eventually cools off and everything goes back to normal. The weak impeller water flow may be enough to idle around on, but once the motor has been run hard it’s not keeping up once off plane and idling again as it’s trying to cool down the hot engine coolant with limited flow. Eventually, the coolant temps come down and your back to idling along happy

 

[Dirty Daytona]

I just replaced the impeller and heat exchanger end gaskets before this trip. Sorry I flaked on you today Peter I was fucking around with this overheating/leaking issue all day!!

 

[Dirty Daytona]

The impeller theory -

The engine is generating a lot of heat while running on plane and hard. When you throttle back come off plane / idle it’s possible the water flow is no longer being “force fed” and reduces due to the weak impeller, yet there is still a lot of heat being transferred from the block / heads to the coolant. The inadequate raw water flow from the weak impeller causes the temps to rise for a bit, in till the coolant eventually cools off and everything goes back to normal. The weak impeller water flow may be enough to idle around on, but once the motor has been run hard it’s not keeping up once off plane and idling again as it’s trying to cool down the hot engine coolant with limited flow. Eventually, the coolant temps come down and your back to idling along happy

That makes sense, thanks for the detailed answer.

 

[Dirty Daytona]

If the head gasket was blown wouldn’t I have water in the oil? Or other issues at all rpm’s?

 

[Guest06]

That makes sense, thanks for the detailed answer.

Did you end up purchasing an VesselView Mobile after all?
You can add the water pressure to your screen and see what it’s running at pressure wise as well.

 

[Dirty Daytona]

Yeah the vessel view was show over 20 psi at speed and between 1 and 3 psi at idle

 

[rrrr]

I just replaced the impeller and heat exchanger end gaskets before this trip. Sorry I flaked on you today Peter I was fucking around with this overheating/leaking issue all day!!

Then something you did is wrong. Maintenance induced problems are common. Check your work again.

 

[Dirty Daytona]

Yeah that could be. However my vessel view readings show good pump pressures.

 

[Dirty Daytona]

Would a faulty reservoir cap cause any of these issues?

 

[Dirty Daytona]

Or is coolant blowing out of the cap because another issue is causing an over pressure in the cooling system?

 

[rrrr]

Or is coolant blowing out of the cap because another issue is causing an over pressure in the cooling system?

You gotta check your gasket installation.

There is a leak between the raw water and coolant in the heat exchanger. The raw water pump pressure at speed is higher than the HE cap holding pressure and it's blowing it out.

 

[JUSTWANNARACE]

16psi cap and running over 20psi explains why its blowing out the cap. Did it do this before you replaced the impeller? If not, I would be checking out the work you did. You may have overlooked something and is now causing the issue you have...

 

[rrrr]

That 19.2 psi is the raw water side pressure.

 

[mjc]

Yeah the vessel view was show over 20 psi at speed and between 1 and 3 psi at idle

Those are good numbers for that.

 

[Dirty Daytona]

16psi cap and running over 20psi explains why its blowing out the cap. Did it do this before you replaced the impeller? If not, I would be checking out the work you did. You may have overlooked something and is now causing the issue you have...

It’s entirely possible I screwed something up but the psi numbers for my water pressure on the vessel view are in the normal range. If what you are saying is true than any pump running over 16 pounds would blow water out of the 16 psi cap. O2howard posted his psi from his vessel view and it was 19 psi and he isn’t blowing coolant out of his 16 psi cap.

 

[braindead]

Have you seen when its dumping coolant, at mid throttle runs or at idle when the temp is high?

 

[gotpablo]

Have you checked your oil cooler? If an impeller has ever failed on that boat there may be impeller pieces caught in the heat exchanger which could cause a restriction of flow through it causing the over heat and potential over pressure.


Sent from my iPhone using Tapatalk

 

[rrrr]

It’s entirely possible I screwed something up but the psi numbers for my water pressure on the vessel view are in the normal range. If what you are saying is true than any pump running over 16 pounds would blow water out of the 16 psi cap. O2howard posted his psi from his vessel view and it was 19 psi and he isn’t blowing coolant out of his 16 psi cap.

Think about this.

Your coolant system has two circulating components that are isolated from each other.

That 19.2 psi is on the raw water (i.e. pump and impeller) side of the coolant system, not the heat exchanger side. HE side normally operates at 12 psi. Raw water side is normally 20 psi max. Cap releases coolant from HE side when system pressure exceeds cap rating of 16 psi.

Your HE side is above 16 psi. Why?

Because your raw water side is comingling with the HE side. That's because you incorrectly installed the gaskets.

Do you get it now?

 

[rrrr]

After thinking a bit, it's also possible you didn't vent the closed loop system properly when refilling it, and there is air in the system. This can cause localized steam pockets under load, which would also show the symptom of pushing coolant out the cap.

Did you follow the instructions for properly filling the system?

 

[FreeBird236]

I believe you have an issue which I'm not smart enough to figure out for you, but you will never eliminate a slight rise in temp after a run. It's completely normal to rise 5-8 degrees after coming off plane, depending on lake water temp. I usually just shift to neutral and bring the revs up to about 1500 and temp drops back in about 10-15 secs. You may have an issue with the water pump housing being honed too many times or maybe it needs to be honed.

 

[WYRD]

Are you sure its coolant leaking or could it be the raw water? I had a similar situation and found I neglected to close th pressure relief valve after using the hand pump to force out the excess raw water.

 

[4Waters]

Pull the plugs on one side of the engine and have the wife crank it over so you can see if water blows out of one of the cylinders then repeat on the otherside. I lost a head gasket on my racecar once and I had no water in the oil but I had overpressure in the cooling system.

Also inspect the plugs as you take them out, the white porcelain around the electrode should be a brownish/caramel color, if one is white that is most likely your cylinder.

 

[Dirty Daytona]

Think about this.

Your coolant system has two circulating components that are isolated from each other.

That 19.2 psi is on the raw water (i.e. pump and impeller) side of the coolant system, not the heat exchanger side. HE side normally operates at 12 psi. Raw water side is normally 20 psi max. Cap releases coolant from HE side when system pressure exceeds cap rating of 16 psi.

Your HE side is above 16 psi. Why?

Because your raw water side is comingling with the HE side. That's because you incorrectly installed the gaskets.

Do you get it now?

When you say gaskets are you talking about the “o ring” type gaskets which go on the tubes from the heat exchanger into the riser? Those seems pretty straightforward

 

[Dirty Daytona]

After thinking a bit, it's also possible you didn't vent the closed loop system properly when refilling it, and there is air in the system. This can cause localized steam pockets under load, which would also show the symptom of pushing coolant out the cap.

Did you follow the instructions for properly filling the system?

Now that I already filled it what’s the best way to purge the system of air?

 

[Dirty Daytona]

Are you sure its coolant leaking or could it be the raw water? I had a similar situation and found I neglected to close th pressure relief valve after using the hand pump to force out the excess raw water.

I’m sure it’s coolant

 

[guest hs]

Are you getting an alarm? Has the boat ever burned up an impeller?

 

[Dirty Daytona]

Not getting any alarms and when I replaced the impeller the old one was not damaged at all but I replaced it anyway. My heat exchanger gaskets were all burned up but the heat exchanger seemed clean. (Before this trip)

 

[guest hs]

If the engine is getting to hot the alarm will go off and put it in Guardian mode. I’m not sure why you think it’s overheating. Make sure you replace those heat exchanger gaskets. If the engine is not overheating and the coolant resivoir cap is new and coolant is still coming out it’s putting compression into the cooling system. Pull the spark plugs and see if any coolant is on the plugs if not check the engines compression.

 

[mash on it]

Maybe pressure test the cooling system?

Dan'l

 

[GRADS]

Replace the impeller and backflush the system to get any parts of the impeller out. Problem solved.

 

[HBCraig]

If you had low water pressure the sensor would sound and shut you down. Trust me, I cahsed this for a year

 

[SoCalDave]

Surprised no one asked if you've tried a different prop...

 

[rrrr]

.

Replace the impeller and backflush the system to get any parts of the impeller out. Problem solved.

.

I see you're paying attention as usual. Stick to subjects you know about, like feather boas.

.

Not getting any alarms and when I replaced the impeller the old one was not damaged at all but I replaced it anyway.

 

[rrrr]

Now that I already filled it what’s the best way to purge the system of air?

It's been so long since I worked on a 496 I don't remember the specifics. Maybe @Shlbyntro can help, he works on a lot of stock 496 engines.

 

[Carlson-jet]

Anytime a heat exchanger is worked on, it should be pressure tested.
I hope it's something simple or nothing.

 

[Albert]

I know those water pumps wear out the brass housing and the water flow becomes weak. They sell a stainless steel one Hardin Marine I believe.

 

[Shlbyntro]

It's been so long since I worked on a 496 I don't remember the specifics. Maybe @Shlbyntro can help, he works on a lot of stock 496 engines.

The end cap gaskets on the heat exchangers only give you access to the raw water side of the exchanger. The exchanger is also on the downstream side of the raw water pump so you would not be having issues with it sucking air here either.. I would rule these gaskets out although it would be smart to blow out the honeycombs with some compressed air. I'm assuming your still having the issue after a new reservoir cap so I'll go a little deeper....

What this issue sounds like to me is one of 2 scenarios. The more likely of the 2 being low water flow in the raw water side of your cooling system. The lesser likely, but not entirely uncommon, as I saw mentioned above is a weaping head gasket/hairline fracture of the head

I would start off by eliminating the weaping head gasket. This will require a radiator pressure tester with an adapter to fit the coolant reservoir on this engine. Your going to want to put the pressure tester on the reservoir and then get the engine up to full operating temperature on a hose. Once your at around the 170 degree mark shut the engine down and pump the tester up to 15psi and it should hold pressure. If it doesn't, then you are likely pushing coolant into the cylinders and you have a blown head gasket. Like I said, this is the less likely scenario but is important to rule out so you're not chasing your tail. With what you're describing, if it is the head gasket it is only a minor leak that is only showing its ugly face with thermal expansion with all the metals and the gasket expanding after you get it hot on a run.

The more likely scenario is low water flow which has a number of causes. But on the 496, the most common causes are restrictions in the raw water side cooling system or a worn out impeller housing. On the impeller, I always run a ball point pen around the outside edge of the groove in the end cap, if it falls into either of the water input/outputs, it needs to be replaced. The groove is preventing the impeller from making a good seal against the housing causing it to pump water less efficiently and the most stressful time on a boats cooling system is coming down to idle right after a hard run. Blockages are normally found inside your heat exchanger end gaskets which you said were clear. I have seen blockages in the drives themselves from debris in the water but this usually causes high speed overheats. On some saltwater bravo boats I have seen restrictions where the corroding gimbal housing closes in on the water hose where it passes through the transom which can also restrict water flow but this is fairly rare. You could also have debris blocking the water flow out of the exhaust risers.

It is important to mention that a bad circ pump could be the culprit but I have only ever seen this on one 496, it's more common in sbc's and older big block.

I did also see above that someone mentioned that you did not say anything about an overheat alarm. Did you just neglect to mention this because the coolant blowout already implied it or did you not have an alarm sound? If not take a infrared gun to see if the engine is actually overheating. The thermostat housing should be reading roughly the same as your engine temp and on that note, a bad thermostat could also be your culprit though it is very rare and I have yet to see this on a 496.

As for bleeding the coolant. It is a self bleeding system. Run the engine through a couple heating and cooling cycles on the hose with the reservoir cap off and top off as needed.

Hope this helps!

 

[Dirty Daytona]

The end cap gaskets on the heat exchangers only give you access to the raw water side of the exchanger. The exchanger is also on the downstream side of the raw water pump so you would not be having issues with it sucking air here either.. I would rule these gaskets out although it would be smart to blow out the honeycombs with some compressed air. I'm assuming your still having the issue after a new reservoir cap so I'll go a little deeper....

What this issue sounds like to me is one of 2 scenarios. The more likely of the 2 being low water flow in the raw water side of your cooling system. The lesser likely, but not entirely uncommon, as I saw mentioned above is a weaping head gasket/hairline fracture of the head

I would start off by eliminating the weaping head gasket. This will require a radiator pressure tester with an adapter to fit the coolant reservoir on this engine. Your going to want to put the pressure tester on the reservoir and then get the engine up to full operating temperature on a hose. Once your at around the 170 degree mark shut the engine down and pump the tester up to 15psi and it should hold pressure. If it doesn't, then you are likely pushing coolant into the cylinders and you have a blown head gasket. Like I said, this is the less likely scenario but is important to rule out so you're not chasing your tail. With what you're describing, if it is the head gasket it is only a minor leak that is only showing its ugly face with thermal expansion with all the metals and the gasket expanding after you get it hot on a run.

The more likely scenario is low water flow which has a number of causes. But on the 496, the most common causes are restrictions in the raw water side cooling system or a worn out impeller housing. On the impeller, I always run a ball point pen around the outside edge of the groove in the end cap, if it falls into either of the water input/outputs, it needs to be replaced. The groove is preventing the impeller from making a good seal against the housing causing it to pump water less efficiently and the most stressful time on a boats cooling system is coming down to idle right after a hard run. Blockages are normally found inside your heat exchanger end gaskets which you said were clear. I have seen blockages in the drives themselves from debris in the water but this usually causes high speed overheats. On some saltwater bravo boats I have seen restrictions where the corroding gimbal housing closes in on the water hose where it passes through the transom which can also restrict water flow but this is fairly rare. You could also have debris blocking the water flow out of the exhaust risers.

It is important to mention that a bad circ pump could be the culprit but I have only ever seen this on one 496, it's more common in sbc's and older big block.

I did also see above that someone mentioned that you did not say anything about an overheat alarm. Did you just neglect to mention this because the coolant blowout already implied it or did you not have an alarm sound? If not take a infrared gun to see if the engine is actually overheating. The thermostat housing should be reading roughly the same as your engine temp and on that note, a bad thermostat could also be your culprit though it is very rare and I have yet to see this on a 496.

As for bleeding the coolant. It is a self bleeding system. Run the engine through a couple heating and cooling cycles on the hose with the reservoir cap off and top off as needed.

Hope this helps!

Thank you very much for the help. I had no alarm sound at all but I did show an engine overheat fault on the vessel view app. I will try the things you mentioned and you have super helpful with your info. I really appreciate it.

 

[SoCalDave]

The end cap gaskets on the heat exchangers only give you access to the raw water side of the exchanger. The exchanger is also on the downstream side of the raw water pump so you would not be having issues with it sucking air here either.. I would rule these gaskets out although it would be smart to blow out the honeycombs with some compressed air. I'm assuming your still having the issue after a new reservoir cap so I'll go a little deeper....

What this issue sounds like to me is one of 2 scenarios. The more likely of the 2 being low water flow in the raw water side of your cooling system. The lesser likely, but not entirely uncommon, as I saw mentioned above is a weaping head gasket/hairline fracture of the head

I would start off by eliminating the weaping head gasket. This will require a radiator pressure tester with an adapter to fit the coolant reservoir on this engine. Your going to want to put the pressure tester on the reservoir and then get the engine up to full operating temperature on a hose. Once your at around the 170 degree mark shut the engine down and pump the tester up to 15psi and it should hold pressure. If it doesn't, then you are likely pushing coolant into the cylinders and you have a blown head gasket. Like I said, this is the less likely scenario but is important to rule out so you're not chasing your tail. With what you're describing, if it is the head gasket it is only a minor leak that is only showing its ugly face with thermal expansion with all the metals and the gasket expanding after you get it hot on a run.

The more likely scenario is low water flow which has a number of causes. But on the 496, the most common causes are restrictions in the raw water side cooling system or a worn out impeller housing. On the impeller, I always run a ball point pen around the outside edge of the groove in the end cap, if it falls into either of the water input/outputs, it needs to be replaced. The groove is preventing the impeller from making a good seal against the housing causing it to pump water less efficiently and the most stressful time on a boats cooling system is coming down to idle right after a hard run. Blockages are normally found inside your heat exchanger end gaskets which you said were clear. I have seen blockages in the drives themselves from debris in the water but this usually causes high speed overheats. On some saltwater bravo boats I have seen restrictions where the corroding gimbal housing closes in on the water hose where it passes through the transom which can also restrict water flow but this is fairly rare. You could also have debris blocking the water flow out of the exhaust risers.

It is important to mention that a bad circ pump could be the culprit but I have only ever seen this on one 496, it's more common in sbc's and older big block.

I did also see above that someone mentioned that you did not say anything about an overheat alarm. Did you just neglect to mention this because the coolant blowout already implied it or did you not have an alarm sound? If not take a infrared gun to see if the engine is actually overheating. The thermostat housing should be reading roughly the same as your engine temp and on that note, a bad thermostat could also be your culprit though it is very rare and I have yet to see this on a 496.

As for bleeding the coolant. It is a self bleeding system. Run the engine through a couple heating and cooling cycles on the hose with the reservoir cap off and top off as needed.

Hope this helps!

And this is why RDP is what it is, people helping people. Great advise and very well explained @Shlbyntro

 

[rrrr]

And this is why RDP is what it is, people helping people. Great advise and very well explained @Shlbyntro

And unlike me, he knows what he's talking about.

 

[Guest06]

That 19.2 psi is the raw water side pressure.

^^ this answers that vv

It’s entirely possible I screwed something up but the psi numbers for my water pressure on the vessel view are in the normal range. If what you are saying is true than any pump running over 16 pounds would blow water out of the 16 psi cap. O2howard posted his psi from his vessel view and it was 19 psi and he isn’t blowing coolant out of his 16 psi cap.

 

[Guest06]

Surprised no one asked if you've tried a different prop...

No he hasn't however that was his plan for Saturday lol.

I have nothing more to add, other than did you get new cap, as well did you test after? Seems crazy, however it’s an 8$ cap so what can it hurt? But if the cap has a crack in it, it could be causing this issue, but that is a large COULD.