Trying lower psi radiator cap
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Senior User
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From: Sacramento
Trying lower psi radiator cap
My '96 4.0 w/178K has a coolant "seep" to exterior, left side head near rear driver side spark plug. Only evidence is gradual coolant loss, and rusty trail. I'm trying a lower psi cap (7 psi, as opposed to 16 or 17)...and some stop leak. I run 4 psi cap on my '51 F1, original radiator but a rebuilt 302, no overheat or boilover problems ever, so am hopeful.
I hate to think of removing 4.0 intake and heads, awful job.Will keep you posted.
I hate to think of removing 4.0 intake and heads, awful job.Will keep you posted.
FTE Community Team
Joined: Nov 2001
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From: Oak Harbor, Washington
The stop-leak will probably work -- for a while.
Your 302 probably does not have the hot spots in its heads like the 4.0l does, nor does it run quite so hot a thermostat, probably; when coolant boils in hot spots (when pressure is not quite enough in the system to maintain coolant in liquid state everywhere: some places are hotter than others), steam does not transfer heat nearly so well as liquid. Overall, you wouldn't see the temp gauge go wild, but you may have areas of the engine overheating from this localized boiling, but no external indication.
What I'm getting at is that you might do better with the stop-leak alone and leaving the OEM system pressure.
The 4.0l has not impressed me with its integrity (cracking heads, head gaskets). Coolant loss seems to be very common, followed by lots of labor.
(The 3.0ls lose coolant too, but not as often from cracked heads or head gaskets.)
Your 302 probably does not have the hot spots in its heads like the 4.0l does, nor does it run quite so hot a thermostat, probably; when coolant boils in hot spots (when pressure is not quite enough in the system to maintain coolant in liquid state everywhere: some places are hotter than others), steam does not transfer heat nearly so well as liquid. Overall, you wouldn't see the temp gauge go wild, but you may have areas of the engine overheating from this localized boiling, but no external indication.
What I'm getting at is that you might do better with the stop-leak alone and leaving the OEM system pressure.
The 4.0l has not impressed me with its integrity (cracking heads, head gaskets). Coolant loss seems to be very common, followed by lots of labor.
(The 3.0ls lose coolant too, but not as often from cracked heads or head gaskets.)
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Joined: Dec 2006
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From: Kitchener,Ontario,Canada
Bear in mind though, that the risk of boil over & evaporated coolant is increased with a lower system pressure. You might well find that you still have to top off the rad even though the ext leak seems to be diminished! Of course for it to boil over is pretty unlikely if the rest of your system is good. 50/50 coolant mixture boils at just over 260*f at 15 PSI. So I believe if the relationship is linear you'll be good for up to about 235*f @ 7 PSI. I've never seen my 3L at over 210 yet.
P.S.mine also uses coolant, dont know where & it amounts to about 200cc/ or less month (less in the summertime!). One of these days I'll get the oil checked but dont think it's going into the crankcase, could be into the combustion chamber, but it does not smell sweet or steam out the exhaust or anything. Does not foul plugs or O2 sensors. Oil level does not change from 0-5000 kms . Maybe like yours it's an external weep which I cant see (highly probable). Also holds pressure for about 10 mins after engine is stopped. I'm almost resigned to live with it!
P.S.mine also uses coolant, dont know where & it amounts to about 200cc/ or less month (less in the summertime!). One of these days I'll get the oil checked but dont think it's going into the crankcase, could be into the combustion chamber, but it does not smell sweet or steam out the exhaust or anything. Does not foul plugs or O2 sensors. Oil level does not change from 0-5000 kms . Maybe like yours it's an external weep which I cant see (highly probable). Also holds pressure for about 10 mins after engine is stopped. I'm almost resigned to live with it!
Last edited by Aeroman59; Feb 3, 2008 at 07:14 PM.
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Joined: Jul 2004
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From: Mitchell, SD
Mine had the leaky heads, heads were checked for cracks and stuff, nothing found, just the gasket let go (I guess it is common with 4.0L) My mechanic remonded putting stop leak in and let it go. I plan on keeping it for another decade or so, so I don't mind putting the cash in it to keep it going.
I would not recomend putting on a lower temp cap, too much chance of overheating and not being able to stop it before it happens.
I would not recomend putting on a lower temp cap, too much chance of overheating and not being able to stop it before it happens.
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Joined: Apr 2005
Posts: 5,720
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From: Washington state
mo51,
bite the bullet and do the head gaskets.
will save your engine and give you piece of mind on trips.
get a small compressor and air tools. stubby ratchets and wrenches. long extensions. makes the job much easier.
do soft freeze plugs at same time
get a helper to install the heads.
good for another 150k
bite the bullet and do the head gaskets.
will save your engine and give you piece of mind on trips.
get a small compressor and air tools. stubby ratchets and wrenches. long extensions. makes the job much easier.
do soft freeze plugs at same time
get a helper to install the heads.
good for another 150k
Last edited by 96_4wdr; Feb 4, 2008 at 04:40 AM.
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Former ******
Joined: Nov 2004
Posts: 4,901
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From: Salt Lake City, Utah
One hint on the stop leak. Don't put in in your system unless you want to replace your heater core. Been there. I'm sure several other people on this forum will back me up, the stop leak products can easily clog the small passages in the heater core and render it useless.
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From: Sacramento
Thanks for input, guys
"bite the bullet and do the head gaskets."
I'll end up there, just not for a few months. I've done the gaskets on my previous ride, a Buick V6 powered Cherokee. Similar lack of elbow room. Hated it. Not looking forward to it, but your tips are good, and I thank you.
I'll end up there, just not for a few months. I've done the gaskets on my previous ride, a Buick V6 powered Cherokee. Similar lack of elbow room. Hated it. Not looking forward to it, but your tips are good, and I thank you.
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