2004 v6 mustang strange issue with coolant system...heat in cabin comes and goes...

[daveinfl33777]

When I first start car it gives me heat out of the vents...I monitor with scan tool the temperature and when it gets around 160 degrees the air is no longer warm and is now cold air....then temp keeps rising even if vehicle is moving it goes all the way to 217 when fans kick on and sometimes up to 223 or 225...as soon as it gets to 217+ I all of a sudden feel EXTREME heat out the vents again...better than before and the engine cools down to 190 and will stay at 190 to 205 the whole time provided I don't sit too long at a traffic light...

To recap: I turn heat on when I start car and it gives me decent heat..on scale of 1 to 10 it provides me with an 8/10....then it blows cold when it reaches 165 degrees or so (I would rate it 0/10 for the heat scale) and then it hits 217+ degrees and I get really nervous and all of a sudden heat comes back (10/10 on heat scale) and the temp of engine comes down fast all the way to normal operating temp 190 to 200 or 205



It's almost like I keep developing an air pocket or something is funky with the tstat? I don't know...I don't know how I would randomly develop an air pocket and then it burps itself out

 

[Mustang5L5]

Seems like an airpocket or a faulty thermostat. After a few hot/cold cycles, air pockets should work themselves out. Are you adding coolant in between engine cycles?

 

[daveinfl33777]

I used to check it but I don't even open it anymore...I never need to add because I'm not losing any...

I wonder how in the world I keep developing these air pockets...

I'm trying to think how a tstat could cause this and I just don't get it. Don't take that as me being cocky and don't think it could be it...my next step is to just change the thermostat...I'm just the rare type of person that needs to know how and why things happen. I want to know the science behind why/how the tstat could cause my exact symptoms...I'm definitley not ruling it out I just want to know how it could potentially be the culprit

 

[Mustang5L5]

First thing I'd do before replacing any parts is pressure test the system. Test if the system holds pressure and if the cap does. V6 cars are notorious for blown head gaskets so i'd want to check for that. Might mean pressure testing the cooling system and/or compression test of the cylinder.

If that checks out, then I would do a coolant flush along with a new thermostat in case that one is sticking for some reason.

 

[daveinfl33777]

I'll do another chemical block test

Crazy thing is it only happens once when I start it and then once it gets going it doesn't overheat at all...I can drive it for 5 hours straight and it will not overheat one bit

It runs at 190 some days on my drive to work...siting idle in this Florida heat with a/c on and it sits at 200 to 205...it's just that initial startup process...

 

[Mustang5L5]

Does rpm seem to affect it? Water pump flow?

That is a very interesting scenario you lay out. All you can do really is perform some basic tests to rule things out.

 

[daveinfl33777]

Does rpm seem to affect it? Water pump flow?

That is a very interesting scenario you lay out. All you can do really is perform some basic tests to rule things out.

Yes rpms do affect it...I feel like I can get more heat out of it if I rev it up...that's why I was thinking maybe it was an airpocket that gets pushed out by the movement of coolant

 

[Noobz347]

My prediction is that your issues will likely be solved with relief type t-stat.

The one on the left.

 

[daveinfl33777]

My prediction is that your issues will likely be solved with relief type t-stat.

The one on the left.

Cool...I will check that out...can you explain why? I'm honestly just interested in all of this...how it all works...I love learning...I'm trying to understand how thermostat would cause heat to come and go or in my case also the engine temp gets really up there (220+) and then all of a sudden a huge increase in heat out the vents and when that occurs the engine temp finally starts dropping and I take a sigh of relief...then I'm good for the rest of the journey...doesn't even come close to 220 again...

I understand how air pockets in the coolant system would cause this but I don't understand the thermostat connection and would like to

 

[Noobz347]

You are getting air trapped in the thermostat housing.

When I first start car it gives me heat out of the vents...

This is normal. Generally speaking, heater lines pull coolant from the portion of the system [before] the t-stat housing and isolated from the radiator when the t-stat is closed.

I monitor with scan tool the temperature and when it gets around 160 degrees the air is no longer warm and is now cold air....

The t-stat [just] opened and your heater core is now mixing with the cold coolant in the radiator.

then temp keeps rising even if vehicle is moving it goes all the way to 217 when fans kick on and sometimes up to 223 or 225...

As the coolant from the warm portion of the engine mixes with the cold radiator coolant, it will rise. The air that trapped in the system and specifically, the t-stat housing is preventing the t-stat from opening at the correct time. The trapped air is keeping the coolant from contacting the t-stat [directly].

as soon as it gets to 217+ I all of a sudden feel EXTREME heat out the vents again...better than before and the engine cools down to 190 and will stay at 190 to 205 the whole time provided I don't sit too long at a traffic light...

Once everything is warmed up, the t-stat is open and functioning normally, it operates as advertised.

To recap: I turn heat on when I start car and it gives me decent heat..on scale of 1 to 10 it provides me with an 8/10....then it blows cold when it reaches 165 degrees or so (I would rate it 0/10 for the heat scale) and then it hits 217+ degrees and I get really nervous and all of a sudden heat comes back (10/10 on heat scale) and the temp of engine comes down fast all the way to normal operating temp 190 to 200 or 205



It's almost like I keep developing an air pocket or something is funky with the tstat? I don't know...I don't know how I would randomly develop an air pocket and then it burps itself out

The air that is suspended in the coolant from air cavitation at the water pump is slowly collecting in the high points of your cooling system.


A t-stat with relief holes allows the fluid to flow over the t-stat sensor even when it is closed. Any air that is trapped in the housing is forced to move through the system and the relief holes.

This allow the t-stat to open [on time] and also allows the hot and cold sides to [slowly] mix at all times so that you don't get that [dip] in temperature that you described when the cold side is opened to the rest of the system.

 

[daveinfl33777]

You are getting air trapped in the thermostat housing.


This is normal. Generally speaking, heater lines pull coolant from the portion of the system [before] the t-stat housing and isolated from the radiator when the t-stat is closed.



The t-stat [just] opened and your heater core is now mixing with the cold coolant in the radiator.


As the coolant from the warm portion of the engine mixes with the cold radiator coolant, it will rise. The air that trapped in the system and specifically, the t-stat housing is preventing the t-stat from opening at the correct time. The trapped air is keeping the coolant from contacting the t-stat [directly].


Once everything is warmed up, the t-stat is open and functioning normally, it operates as advertised.



The air that is suspended in the coolant from air cavitation at the water pump is slowly collecting in the high points of your cooling system.


A t-stat with relief holes allows the fluid to flow over the t-stat sensor even when it is closed. Any air that is trapped in the housing is forced to move through the system and the relief holes.

This allow the t-stat to open [on time] and also allows the hot and cold sides to [slowly] mix at all times so that you don't get that [dip] in temperature that you described when the cold side is opened to the rest of the system.

Thank you very much for this detailed response. I greatly appreciate it!

For whatever crazy reason I just started my car and it had cooled down...so when it cools down is when this same thing happens and for whatever reason it didn't happen...had good heat from from startup all the way to 180 degree engine temp...and at 180 I was saying wow this might be actually for the first time in a very long time not act up and do it's normal thing (lose heat and then temps spike to 220+ and then finally heat returns and engine temp stabilizes for rest of journey)

Sure enough it got to a high of 199 and didn't go in the 200s...and it never lost heat one time...gave me hot heat the entire time.....that's the first time in a very long time that it behaved correctly....

Now I'm wondering if maybe the air pocket that it continuously creates "hides away" in the coolant reservoir until I start it back up and then it gets into the system and the high points like you mentioned....I wonder if the problem is this air pocket is never fully burped out of the system...the only thing I did different is the last time I started it I let it warm up with the coolant overflow tank cap off...I never do that...maybe that allowed it to burp? Because it's very odd that it actually acted completley normal like it should after doing this....and honestly it would do this crap of going up to 220+ and loss of heat 50 of the last 50 start ups

 

[daveinfl33777]

You are getting air trapped in the thermostat housing.


This is normal. Generally speaking, heater lines pull coolant from the portion of the system [before] the t-stat housing and isolated from the radiator when the t-stat is closed.



The t-stat [just] opened and your heater core is now mixing with the cold coolant in the radiator.


As the coolant from the warm portion of the engine mixes with the cold radiator coolant, it will rise. The air that trapped in the system and specifically, the t-stat housing is preventing the t-stat from opening at the correct time. The trapped air is keeping the coolant from contacting the t-stat [directly].


Once everything is warmed up, the t-stat is open and functioning normally, it operates as advertised.



The air that is suspended in the coolant from air cavitation at the water pump is slowly collecting in the high points of your cooling system.


A t-stat with relief holes allows the fluid to flow over the t-stat sensor even when it is closed. Any air that is trapped in the housing is forced to move through the system and the relief holes.

This allow the t-stat to open [on time] and also allows the hot and cold sides to [slowly] mix at all times so that you don't get that [dip] in temperature that you described when the cold side is opened to the rest of the system.

You mentioned the tstat just opened causing the cold coolant to mix in the heater core...at 160 degrees? Isn't it supposed to open at 190? Could a bad thermostat be opening it way too early? Just because it's defective?

 

[Noobz347]

You mentioned the tstat just opened causing the cold coolant to mix in the heater core...at 160 degrees? Isn't it supposed to open at 190? Could a bad thermostat be opening it way too early? Just because it's defective?

That's possible. I could also be opening late because it's surround in an air pocket.

 

[daveinfl33777]

That's possible. I could also be opening late because it's surround in an air pocket.

Is my theory possible regarding sir pockets never getting burped completley out of the system and instead just "hiding" in the coolant reservoir?

Since I am getting these weird symptoms of air pockets...only after it cools for a while....and once it clears they do not return until car has been off for several hours....I'm thinking these air pockets aren't being produced by anything but instead from improper coolant fill originally months ago...and it never burped it out completley...could air pockets "hide" in the coolant reservoir where it has no impact on the coolant system and then re-emerge when engine temp cools and it gets sucked back into the coolant system?

May sound like stupid theory but it's all I got right now and it does match my symptoms...I'm at this point convinced I'm getting air pockets and now I'm just trying to find out why/what is causing it....and if it's actually possible for air pockets to make it to coolant reservoir and stay there to come back in coolant system later then it would be exactly what's happening with me