No Pressure In Coolant System and Not Overheating?

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tony1679

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I am working on my sister's 2003 Mercury Grand Marquis 4.6L. I just finished replacing the intake manifold due to broken plastic next to a gasket below the thermostat housing. The thermostat seal was split in multiple places, and I thought that was the problem originally. I want to clarify the car had no interior heat prior to any repairs, and still doesn't. Now there is a new manifold, new thermostat, and seal. The coolant reservoir is full, and the car warms up quickly (normal), much faster than before with a bad seal. The engine never got hot (above normal operating temp) before, and still doesn't. There are no coolant leaks after replacing the manifold, and no leaks from the cap.

I am not dumb, I do this with caution (and don't recommend anyone else doing this), but with the car fully warmed and still running I can remove the coolant cap. By remove I mean remove it quickly, because there is almost zero pressure built up.

Here are my thoughts, but please give yours. I think there can only be 3 possibilities.
1- Bad cap. I think this is likely.
2- A clog somewhere. Maybe...
3- Bad water pump. I don't think this is the case. If this is, shouldn't it overheat?

I don't think it's the heater core, but I'm not 100% positive. No, there is no coolant in the lines going to and from, but both are very hot. If there was a clog in the heater core, one hose should be colder, right? And if it's leaking, it would wet the passenger floorboard, and that's not happening.

Thanks in advance for any advice and help!
 
Sometimes there is a water shut off valve in the lines to the heater core. This valve closes when A/C is in use. Perhaps you have one and it is malfunctioning in the closed position.
 
Originally Posted By: WobblyElvis
Sometimes there is a water shut off valve in the lines to the heater core. This valve closes when A/C is in use. Perhaps you have one and it is malfunctioning in the closed position.
I think this 'switch' I keep hearing about is the culprit of not having heat, and I already somewhat suspected this, but would it cause NO pressure in the entire system? And wouldn't coolant still be in one of the two lines?
 
Unless you drive the car for a good half hour, it is not really up to temp and may not pressurize. Coolant/water mix does not boil under 260F or more and you may have a 180F stat.
With the hoses off the heater core simply try to blow water or air through it. Should be a simple test to see if it's plugged. You should also be able to blow air/coolant through the engine block via the heater lines to that normally go to the heater core.
Removing the rad cap on a hot engine is very DANGEROUS !
 
I would try the a new radiator cap. How do the upper and lower radiator hoses feel? Upper one should feel hot and the lower a little cooler.
 
try one of the radiator funnels (they are usually green and large) this will burp the system if there are air pockets. you will also see if there is any pressure as the coolant will rise and fall in your funnel.
 
Another thing to check is if the blend door for the heater core/a/c unit is stuck in closed position. This would restrict all air flow through the a/c side and close off the heater core from the airflow path. You would only see air flowing through the a/c side which would be ambient air temperature.
 
Replace the cap. Those ford cooling caps always go bad. I had a bad cap and no pressure in the cooling system of my '00 Town Car, it wouldn't overheat but the hoses were always soft. A new cap got the pressure back.

The no heat problem could be some sort of blend door problem like others have said.
 
For no pressure, it's almost definitely a bad cap. I see tons of cars with them failed. Just be aware, depending on how long it's been bad, you might find some new leaks once it's building pressure properly again.
 
Originally Posted By: rslifkin
For no pressure, it's almost definitely a bad cap. I see tons of cars with them failed. Just be aware, depending on how long it's been bad, you might find some new leaks once it's building pressure properly again.


Yes, just like an air conditioning system that was running low pressures, bringing it back up to spec pressure is a good way to locate anything else that might be marginal.
 
Originally Posted By: tony1679
I am working on my sister's 2003 Mercury Grand Marquis 4.6L. I just finished replacing the intake manifold due to broken plastic next to a gasket below the thermostat housing. The thermostat seal was split in multiple places, and I thought that was the problem originally. I want to clarify the car had no interior heat prior to any repairs, and still doesn't. Now there is a new manifold, new thermostat, and seal. The coolant reservoir is full, and the car warms up quickly (normal), much faster than before with a bad seal. The engine never got hot (above normal operating temp) before, and still doesn't. There are no coolant leaks after replacing the manifold, and no leaks from the cap.


Hot heater hoses and no heat generally indicates a blend door problem in heater plenum... Can't have both heater hoses hot if it isn't circulating... If you have the EATC system it'll be throwing error codes...

A bad cap will not cause no heat nor overheating(at least if it isn't loosing coolant)...

I ran my '98 with the all plastic intake for four years with cap loose, never had a issue but the POS intake cracked anyway... At least it was just a dribble vs instant dump of coolant...
 
If it has a pressurized overflow tank make sure there are no cracks in it. My Tauruses would crack on the bottom.
 
Originally Posted By: WobblyElvis
Unless you drive the car for a good half hour, it is not really up to temp and may not pressurize. Coolant/water mix does not boil under 260F or more and you may have a 180F stat...
Removing the rad cap on a hot engine is very DANGEROUS !
The cap can be removed without hesitation after running 3+ hours (and still on). No change. As I said, I changed the thermostat, and know for certain it is 192 degrees, just like OE. Last, again, I'm not dumb. I know what I'm doing when removing a cap.
Originally Posted By: ARB1977
I would try the a new radiator cap. How do the upper and lower radiator hoses feel? Upper one should feel hot and the lower a little cooler.
They both are very warm, and both only have a small amount of fluid in them. Both can be squeezed easily.
Originally Posted By: krismoriah72
try one of the radiator funnels (they are usually green and large) this will burp the system if there are air pockets. you will also see if there is any pressure as the coolant will rise and fall in your funnel.
I'm not sure how this would help me. Perhaps you could explain?
Originally Posted By: 03cvpi
Another thing to check is if the blend door for the heater core/a/c unit is stuck in closed position. This would restrict all air flow through the a/c side and close off the heater core from the airflow path. You would only see air flowing through the a/c side which would be ambient air temperature.
Judging by your username, you drive this car's twin sister. Crown Vic Police Interceptor, right? I'll look into this, although I don't know what to check. If it helps, the heat blows the same as the outside temp. But A/C was/is working perfectly. And all modes work correctly (defrost, floor, vent, etc.).
Originally Posted By: Chris142
are both heater hoses hot?
In my original post: "I don't think it's the heater core, but I'm not 100% positive. No, there is no coolant in the lines going to and from, but both are very hot."
Originally Posted By: rslifkin
Just be aware, depending on how long it's been bad, you might find some new leaks once it's building pressure properly again.
I wouldn't have thought of that, thanks for the warning.
Originally Posted By: TFB1
Hot heater hoses and no heat generally indicates a blend door problem in heater plenum... Can't have both heater hoses hot if it isn't circulating... If you have the EATC system it'll be throwing error codes...

A bad cap will not cause no heat nor overheating(at least if it isn't loosing coolant)...

I ran my '98 with the all plastic intake for four years with cap loose, never had a issue but the POS intake cracked anyway... At least it was just a dribble vs instant dump of coolant...
Hmmm this sounds strangely familiar...... Thanks for the advice.
Originally Posted By: SHOZ
If it has a pressurized overflow tank make sure there are no cracks in it. My Tauruses would crack on the bottom.
Good advice, but I think it's fine. No noticeable leaks, but I will double check.

Thanks again everyone.
 
Update - I replaced the cap. After driving for two hours, same story, I can take off the cap. In its defense, this one feels tighter and when removing it I do hear a tiny hiss. But still no measurable pressure. The only positive change I notice is that there seems to be more coolant in the upper and lower radiator hoses. But I can still squeeze both. After finding this, I also noted that the lower radiator hose is noticeably cooler than the upper, so things are slowly going the right direction.

So now what? New intake, new thermostat, new cap, and a reservoir full of coolant, what's left? Thanks in advance.
 
Originally Posted By: Garak
One obvious thing that comes to mind is the mating surface between the new cap and the neck. Is the neck corroded up? I have come across that over the years.
Nope, clean as new.
 
if it gets to temp then the thermostat is working, the pressure issue then would be either with a internal coolant leak in the motor(which you should have seen evidence by now) the radiator cap not holding pressure, or a pocket of air in the system if you have not bled the air yet.

I am attaching a video of how to bleed a cooling system, there are many videos so feel free to choose another.

https://www.youtube.com/watch?v=xYkKW0OyeUc


If bleeding the cooling system does not work, you will need to pressure test the system, you may have a small weephole leak in your waterpump etc that you do not know about etc.
 
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