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Putting my 4.7 HO back together after a head gasket job. Replacing the thermostat with a new one preventively as the engine overheated. Thermostats are in the category of "things I only get from the dealer" and the current MOPAR part number for my VIN is 52079476AE. What the local MOPAR dealer sold me was a MotoRad-branded unit with "476AE" and the DC pentagram stamped into it.

The thermostat I removed from the engine is a 52079476AB. Same part number, earlier revision. They are noticeably different in that the new one (rev AE) is missing a protrusion at the base of the wax motor which is designed to partially block the coolant bypass port when the thermostat open. This is described in my 02 FSM, for your convenience this post covers it in the same level of detail.

I've seen people have bad experiences when using non-bypass thermostats in cooling systems that have bypass ports, but everything I can find online suggests that Chrysler deliberately deleted the bypass stem feature from their thermostats in this application. There's a comment on the above-linked thread that aligns with my observations. Can anyone shed any additional light on this?

Thanks,
Tony
 

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Putting my 4.7 HO back together after a head gasket job. Replacing the thermostat with a new one preventively as the engine overheated. Thermostats are in the category of "things I only get from the dealer" and the current MOPAR part number for my VIN is 52079476AE. What the local MOPAR dealer sold me was a MotoRad-branded unit with "476AE" and the DC pentagram stamped into it.

The thermostat I removed from the engine is a 52079476AB. Same part number, earlier revision. They are noticeably different in that the new one (rev AE) is missing a protrusion at the base of the wax motor which is designed to partially block the coolant bypass port when the thermostat open. This is described in my 02 FSM, for your convenience this post covers it in the same level of detail.

I've seen people have bad experiences when using non-bypass thermostats in cooling systems that have bypass ports, but everything I can find online suggests that Chrysler deliberately deleted the bypass stem feature from their thermostats in this application. There's a comment on the above-linked thread that aligns with my observations. Can anyone shed any additional light on this?

Thanks,
Tony
Some claiming to be Mopar here.

https://www.google.com/search?q=520...hUKEwjd66mD04PxAhU8AGMBHcz4DjUQ4dUDCA4&uact=5
 

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Tanx for the links to info on the Thermostat Coolant Bypass Block Off! I never thought of Thermostats that way, but looks like I'm adding that to my list of "Stuff I only get from the dealer"...
 

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WJ 4.7 HO my 2002
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Uhmmmm....

I wonder if there could be some relationships between the different Tstat design and the sudden valve seal drop.....:unsure::unsure::unsure::unsure:
 

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In the olden days, cars had summer & winter t/stats.

Come Autumn / Spring, smart old timers changed
their oil & thermostats.

Wise owners checked their t/stats
before they fitted them.
 

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A WJ t/stat should start to open at 195F.
It should be completely open at 215F.

If you live in a hot climate
you could use a t/stat
with a lower temp rating.

If you live in a cold climate,
you could use one with a higher rating.

If you are worried about valve seats
you could calm your nerves
with a say, 185F stat.

Mind you, no guarantees ;)
 

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'01 Limited 4.7L Quadradrive
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Both the 4.0L and 4.7L engines use 195° thermostats for all model years from 1999-2004. When replacing a thermostat it is very important to install one with the same temperature rating (the only exception might be with certain performance modifications or chips that recommend or require a different temperature thermostat). No benefits or performance gains can be realized by installing a "cooler" thermostat into a stock engine. Doing so is not recommended, it will give you colder heat in the winter and may interfere with engine performance.
A thermostat rated lower than the factory thermostat will richen your fuel mixture a bit at the expense of gas mileage, increased exhaust emissions and dirtying your oil faster - not to mention shortening the life of your cylinder walls and catalytic converters and more frequent spark plug changes. The unnoticeable performance gain, if any at all, is simply not worth the potential drawbacks.
 
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Both the 4.0L and 4.7L engines use 195° thermostats for all model years from 1999-2004. When replacing a thermostat it is very important to install one with the same temperature rating (the only exception might be with certain performance modifications or chips that recommend or require a different temperature thermostat). No benefits or performance gains can be realized by installing a "cooler" thermostat into a stock engine. Doing so is not recommended, it will give you colder heat in the winter and may interfere with engine performance.
A thermostat rated lower than the factory thermostat will richen your fuel mixture a bit at the expense of gas mileage, increased exhaust emissions and dirtying your oil faster - not to mention shortening the life of your cylinder walls and catalytic converters and more frequent spark plug changes. The unnoticeable performance gain, if any at all, is simply not worth the potential drawbacks.
That seems plausible WJ.

Where did you get such a definitive statement from please?
 

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Thanks WJ, that certainly seemed pretty authoritative
until it came to the bit about "Cooler heat."
Perhaps "Cooler heat" is an Americanism,
but it sits uncomfortably with me.
I'm not American by the way.

I felt a little left in the dark too
as the learned article
made no reference to the relationship
between oil temp and ambient temp.

It seems beyond argument,
that once the car coolant has come up to temp,
the oil temp in a car crossing
a hot desert at noon in summer
will be higher than the oil temp
in a car crossing a cold desert
just before dawn.
Or have I got that wrong?

If I'm right, doesn't it make sense to balance things out a bit,
by varying the coolant temp slightly?

As for the gizmos varying mixture with coolant temp,
I understand that induction air temp
plays a large part in mixture regulation.

Isn't that much of the underlying science behind
why folks seeking cooler induction air?

Or have I got my knickers in a twist there please?

What are you opinions here please cD?
Or anyone else happy to add their threepence worth?

PS, whilst most of the above comes from
stuff I've picked up along the way,
Napa seems to see things my way.
Then again, Napa may be distorting the facts
to increase sales I suppose.
 

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You're overthinking stuff. I go with the belief that engineers know what they're doing.
 

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WJ 4.7 HO my 2002
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@Delta0,
I think that @WJ60 want to say that our 4.7 are relatively new engines, built using simulation technology that can create different ambient and performance conditions, so there is no need to use practices that were used in "classic" cars, built in '60s, '70s, '80s.

I still have the original Tstat in my jeep, and I have no intention to change it with a "cooler" one.

My initial question was because I would like to find "the key", something that can be related to the valve seat dropping, something different from the usual hypothesis that see the simple "bad batch of valve seat" or "bad batch of heads" or "poor head/seats design".

I am curious to know if in my 4.7 the Tstat has that stem or not..., really curious...; for sure I know that the OEM spare one that I have bought some years ago (never installed, I have it somewhere in the WJ cargo area😂) does not have that stem....
 

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@Delta0,
I think that @WJ60 want to say that our 4.7 are relatively new engines, built using simulation technology that can create different ambient and performance conditions, so there is no need to use practices that were used in "classic" cars, built in '60s, '70s, '80s.

I still have the original Tstat in my jeep, and I have no intention to change it with a "cooler" one.

My initial question was because I would like to find "the key", something that can be related to the valve seat dropping, something different from the usual hypothesis that see the simple "bad batch of valve seat" or "bad batch of heads" or "poor head/seats design".

I am curious to know if in my 4.7 the Tstat has that stem or not..., really curious...; for sure I know that the OEM spare one that I have bought some years ago (never installed, I have it somewhere in the WJ cargo area😂) does not have that stem....
You might be right Mak :)

By "Key", do you mean a link
between dropped seats,
and the cause.

If so I suggest you look no further
than the rigmarole involved
in burping air out of the cooling system.

AKA poor maintenance.
 

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Waaaay back in the 80's I lived in the desert, it was common practice to remove the stat completely. Of course many could not figure out why their junk was still overheating. Trying to explain to them the restriction is needed to keep the coolant in the actual radiator as long as possible for maximum heat exchange was futile.
 

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Waaaay back in the 80's I lived in the desert, it was common practice to remove the stat completely. Of course many could not figure out why their junk was still overheating. Trying to explain to them the restriction is needed to keep the coolant in the actual radiator as long as possible for maximum heat exchange was futile.
Was the tap water in your desert "Hard" water please cD?
 

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WJ 4.7 HO my 2002
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@cDee63,
So..., that stem seems to be not only useful, but really necessary!

I wonder why Chry has modified the tstat deleting that stem…🤔: there will be a technical reason, ….or the usual stupid cost reason?
 
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