Could a new radiator cap blow out the headgasket completely on the '96 D.A.?

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sprocket

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So here's the deal. The D.A. has been filling up the reservoir with coolant and then overflowing at the cap. Then the coolant is low. If I rev the engine at idle, there is no bubbling in the reservoir which would be a sign of a blown head gasket. I know this can be a sign of a bad cap that is not holding pressure, so I got a new cap. When I went to bleed the system the coolant looked like foam. There was massive air in it. I noticed the old cap looked bulged at the top.

I'm thinking my head gasket problem has returned even though it passes the hydrocarbon test. I'm imagining it has a very small head gasket breech that is causing the cooling system to get more and more air in it over time. When there is no more room for the coolant/air mixture, it pushes out the cap. Over time this causes the cap to fail, then the coolant can easily escape the cap which in turn loses coolant and causes an intermittent "low coolant warning". Since more air is always being introduced, the level in the system is sometimes high enough for the coolant warning to stay off.

It's actually surprising that it doesn't overheat, but it does get up to the O in NORMAL if I drive it long enough and it is hot enough out. I really haven't driven it for much more than about 30 miles at a time. Also, it has no thermostat (the center is cut out). I did that as a test awhile ago and still haven't put a new one in.

So, back to the question: Now I've bled the system and the new cap is in place. Since the new cap should hold a good seal will this force the coolant/air to escape somewhere else? Like by blowing out the head gasket? Or is the cap designed to let coolant out if the pressure builds too high? Or am I maybe barking up the wrong tree. Is it possible that the only reason there is air in the system is because the cap was bad?

Sorry for the long post, but I like to get all the detail out there for the most informative responses. Thanks!
 
do you have coolant in your oil? its not overheating its actually staying bellow normal.....why do you think your headgaskets are toast?
 
PhantomVIII said:
do you have coolant in your oil? its not overheating its actually staying bellow normal.....why do you think your headgaskets are toast?
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One of the head gaskets is toast. There's no question of that. I've written about it before. It failed the hydrocarbon test, there was oil in the coolant but no coolant in the oil, and there was back pressure into the coolant reservoir, and I had overheating. I used Blue Devil on it. I used the mechanics stuff which required me to completely flush the system and add the Blue Devil without a thermostat. After that it passed the hydrocarbon test and continues to do so.

There is still oily film in the reservoir, but I was told that it is pretty hard to flush all the oil out and it could be left over from before I used Blue Devil. I don't know. The oil is not low and there is no coolant in the oil.

I've been asked why I don't just replace the engine. It's because it gets me from here to there and I am a cheapskate who will milk this engine for all it's worth. At some point I may just sell it. I've gotten my money out of it. I'm at probably $1200-$1400 and have had it for 7 months. I drive it 25 miles to work most of the time.
 
You have a blown headgasket, you know this yet you want to know if a rad cap will blow it more? Its like pregnancy. You are preggers or not, cant be just a little. Head gasket is bad, its bad. Time for a new motor. They are cheap used. Ive paid $200-$500 for good Mark motors.
 
Have you tried a new O.E. motorcraft thermostat? That overflowing at the cap is exactly what happened to me when it got hot until I replaced the thermostat.
 
sprocket said:
One of the head gaskets is toast. There's no question of that. I've written about it before. It failed the hydrocarbon test, there was oil in the coolant but no coolant in the oil, and there was back pressure into the coolant reservoir, and I had overheating. I used Blue Devil on it. I used the mechanics stuff which required me to completely flush the system and add the Blue Devil without a thermostat. After that it passed the hydrocarbon test and continues to do so.

There is still oily film in the reservoir, but I was told that it is pretty hard to flush all the oil out and it could be left over from before I used Blue Devil. I don't know. The oil is not low and there is no coolant in the oil.

I've been asked why I don't just replace the engine. It's because it gets me from here to there and I am a cheapskate who will milk this engine for all it's worth. At some point I may just sell it. I've gotten my money out of it. I'm at probably $1200-$1400 and have had it for 7 months. I drive it 25 miles to work most of the time.
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Sounds like an intake gasket to me. You're getting oil in the coolant from the PCV system. I've seen this happen on countless GM 3800s.
 
there is no coolant or oil in the mark viii intake. anywhere.

he has a blown headgasket. its that simple.
 
Caps are rated for PSI its on the cap if you look.
Its 16 PSI I believe.
It will release at that pressure.
If you bought the same PSI cap, the cap is not the issue.
Metro auto "Lakeville" still has a 2004 c head for $1500, its your best option IMHO.

Last thing I would do is buy another high mile b head engine.
 
a little oil i suppose, but when i had my intake apart at 180k, there was more carbon buildup from the EGR than anything else.
 
ford nut said:
Caps are rated for PSI its on the cap if you look.
Its 16 PSI I believe.
It will release at that pressure.
If you bought the same PSI cap, the cap is not the issue.
Metro auto "Lakeville" still has a 2004 c head for $1500, its your best option IMHO.

Last thing I would do is buy another high mile b head engine.
Click to expand...

Yes both caps should have just released pressure at 16 lbs, but there must be SOME difference between the old and new cap. Now with the new cap, the hard start is back. It acts like coolant is being forced into the cylinder. There was a bad misfire on the first start this morning but it went away after a minute.

I really need to stop writing about this thing. It needs an engine and I need to do that or sell it. I'm not willing or able to sink much into it. I think I'm ready to start taking offers....
 
Yeah, she's really toast now. The new cap holds 16lbs pressure, so as soon as I shut the car off and there is no compression, the cooling system pressure forces coolant through the breech and into one or two cylinders. Then it is a nightmare to start after it sits for awhile.
With the old cap, which held no pressure, the HG leak forced air into the coolant which then caused the recovery tank to overflow. Since there was no cooling system pressure, coolant did not enter the cylinders when it was not running, so it was easy to start. I have no explanation as to how it can be passing the hydrocarbon test.

I'll have to stop driving it until I sell it or change the engine. In order to drive it now I have to release the pressure on the cap whenever I shut it off and it is going to sit for awhile. That's the only way to prevent coolant from being pushed into the cylinders.

It's also amazing that it doesn't overheat.
 
It probably does over heat... you're losing coolant thru the cylinder breach, the coolant temp sensor is in the crossover tube on the driver side.. when the coolant is low the sensor will only be reading the air temperature

If you know its a bad head gasket.. get "Liquid Glass" and quit playing around
 
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