Anyone know if I can get a 205F thermostat for a 4L engine? - JeepForum.com
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Unread 04-12-2013, 02:29 AM   #1
Charley3
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Anyone know if I can get a 205F thermostat for a 4L engine?

I want a 205F thermostat for a 1999 XJ.

Trying to figure out what brand and part number 205F thermostat to get for 4L Jeep.

Edited in Later:

I have done this on a prior 4L Jeep and a Buick. Both times it worked great, but I can't remember what thermostat to get for 4L Jeep.
Before someone asks why I want to put a 205F thermostat in a 4L Jeep engine, it is because the warmer engine will get about 3 better mpg in Winter, 2 mpg better in Fall and Spring, and 0 to 1 mpg Summer.

There will be little or no change in mpg on hot Summer days because it'll be same engine temp as with stock 195F thermostat on a hot Summer day.

The goal is to run at same engine temp year round as it already runs in the Summer to get Summer gas mileage year round.

Running at 205F won't hurt it.The electric fan doesn't even come on until 215F, and I'm using 5-40 Mobil One synthetic.
Edited in Later:
I decided to get 205F thermostat brand ACDelco, part number 12TP1F because it fits all 4L Jeeps with no modification, and is a quality brand.

Gates 33010 is another 205F thermostat option for 4L engine.

See post 16 for more info about those thermostats.


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Unread 04-14-2013, 11:43 AM   #2
TDIJeep
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As much as i know this does work in some applications i beileve it is better used on a diesel or something that produce a larg amount of heat and requires it to be removed this lowers EGT which increases boost and thus power and ecomony. Things that increase mileage are not equal across the board, all depends on what factors are most effecting your engines economy.

People cut louvers in there hood to remove all that heat and that's with a 195, 205 will be even hotter and some engines and coolants will not put up with it for very long.

diesels already use auto ignition thru fuel injection but gasoline air/fuel i thinkin could cause pre detonate due to compounding heat and presssure.

not so sure about the 4.0 but some times older engines have similar thermostats with different heat specs maybe look in to the 4.2

Have you seen this used in a gasoline application, drop a link i would like to read about this in a gasoline engine.
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Unread 04-14-2013, 04:39 PM   #3
Charley3
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I switched my Buick Park Ave thermostat from 185F to 195F and gained 3 mpg.
OEM thermostat is 195F. It's supposed to have a 195F, but prior owner had put in a 185F.
2 years later I switched it to 205F and gained 1 mpg.

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On a 2006 LJ Rubi I switches thermostat from 195F to 205F and gained 2 mpg.

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A little warmer runs more efficient and cleaner. That's part of why gas mileage is better in Summer. The heater works better in Winter too. 4L runs most efficient (and clean) at 205 to 212F. Same with my Buick 3.8L. Those are temps they run at most of time in Summer stock. That doesn't change in Summer. What changes is Winter op temp warms up to similar to Summer. Winter gas mileage is improved and closer to Summer mpg.

Oil, plugs, valves all stay cleaner. No change in power that I noticed. Make Winter running more efficient like Summer. It's perfectly safe. Still runs cooler most of the year than temp that triggers electric fan (in Buick or XJ). In Summer the electric fans come on sometimes, but that would happen with OEM thermostat too.

---

So I have done this before and it works. Largest mpg improvement occurs when you have a cold air intake (like my Buick) and all electric cooling fan(s) (like my Buick), but the warmer temp does benefit a stock 4L about 2 mpg in Fall, Winter, and Spring. No difference in Summer. Benefit increases when you have cold air intake and electric cooling fans. XJ has one electric fan stock. I might convert XJ to all electric fans and cold air intake.

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Gas (and diesel) burn more efficiently when hotter. However, cold air is denser and has more oxygen. So combine a hot engine with cold air intake and electric fans (that don't need to come on, except in Summer) and you have increased efficiency. This is exactly what car makers are doing on new cars to get better mpg. A good conventional oil can handle 205F to 215F all the time, but I'm only making it run 205F most of year. In summer on hills at low speed, or in traffic jams, it will run between 210F and 215F and that is just fine. It'd be that same temp range in Summer with stock 195F thermostat because electric fans(s) come on at 214F in my car and XJ.

I would be fine doing that with a good conventional oil like Chevron, Shell, Mobil or others. But I am using Mobil One synthetic 5/40. So I have over kill protection.

Gas engines are fine all the way to 220F for sure. I used to have a 96 XJ with a bad electric fan sensor. It ran 230F every summer for 12 years. It still ran great 60K miles later.

So I know 220F and lower won't hurt an engine. My engine only occassionally hit 215F on a hot Summer day in a traffic jam or slow spees hill climbs. Even when they do occasionally get to 215F and electric fan(s) come on, within 30 seconds fans cool it down to 210F or 212F. Most of the Summer and all the rest of the year it runs 200F to 205F.
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Unread 04-14-2013, 04:42 PM   #4
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Problem is I had to find a 205F made for another car that almost fit, and then grind the gasket mating flange 1/16" smaller. A pain in the butt. Now that I'm very handicapped, I'd have to hire someone do that for me, which costs money and defeats the money savings of the improved fuel economy.

What I need to find is a 205F thermostat that fits 4L without mods.
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Unread 04-14-2013, 09:17 PM   #5
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I have seen this in practice but had to be made out of parts from two seperate stant thermostats, a hybrid thermostat. I would call stant with measurements of your thermostat and have them compare it to other motors with similar sized stats. Maybe the parts could be interchange as i believe that pellet cartidge effects opening temp.

I do believe that this will work to save money at the pump, I'm just unsure whether you will be out money when it comes to maintanence in the long run.

Curious how a plastic end tanks rad put up with this as they seem to often crack with 185 stat.

Hey man, all the power to yea, and good luck, Im wondering how this will play out in the long run.
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Unread 04-14-2013, 10:50 PM   #6
Charley3
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Many new cars run at 205F to 210F.

Do they have platic radiator tanks?

My LJ had plastic tanks. Never bothered them. My XJ has metal tanks.

All I'm doing is making it run at normal Summer temps year round to get Summer gas mileage year round.
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Unread 04-15-2013, 07:02 AM   #7
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Jeep stat is the same as many GM products.
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Unread 04-15-2013, 12:56 PM   #8
Charley3
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Quote:
Originally Posted by cruiser54 View Post
Jeep stat is the same as many GM products.
Do you mean I can shop GM stat inventory? If so, that might be a solution for me to find a 205F stat that will fit my XJ without having to grind or otherwise modify it.
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Unread 04-15-2013, 01:08 PM   #9
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What do you think of FailSafe thermostats? Good stuff?

A JF forum member posted that he bought a Fail Safe, a Stant, and an OEM for his XJ.

Then he boiled each in a pot with a thermometer.

He said:

Stant opened at 190F (to cold to let engine get to full op temp in Winter, IMO)

OEM opened at 195F (good, but not ideal, IMO)

Fail Safe opened at 205F (perfect, IMO)

So apparently I could just use a Fail Safe brand stat for 4L, or I could buy several brands and test them with a thermometer in pot boiling water. Either way, a perfect fit with no mods required.

Or I could shop for a brand advertised as 205F for other cars until I find one that phyically fits.

Your recommendations?

Edited in Later: Fail Safe does not make a 205F for 4L Jeep. They do make a 192F, which allegedly really opens at 205F. So that could possibly work, but I am going with an ACDelco 205F stat.
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Unread 04-15-2013, 02:38 PM   #10
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Factory stat from the dealer.
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Unread 04-15-2013, 10:35 PM   #11
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Try these for 205* stats

Stant 13352
Gates 33010
NAPA 383
AC Delco 12TP1F
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Unread 04-15-2013, 11:24 PM   #12
Charley3
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Quote:
Originally Posted by jnicewan View Post
Try these for 205* stats

Stant 13352
Gates 33010
NAPA 383
AC Delco 12TP1F
You think they'll fit?

I'll check those ^ 205F for fit.

I'll also check the Delco ones Cruiser mentioned.

I might also buy a few brands of 195F made for 4L because some of them (like Fail Safe) might actually open arounx 205F.
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Unread 04-15-2013, 11:36 PM   #13
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Quote:
Originally Posted by Charley3 View Post
You think they'll fit?
You can research it yourself, I did a little google-fu for ya out of curiosity. In fact on the RockAuto site it lists the A/C Delco as a match for Jeeps, but the thermostat Jeep uses is used in many GM and Ford apps too.

205 stats are hard to find and/or get info on, probably because most of them never had an OEM application. Either match it up at the parts house or compare the dimensions online, the most I saw different on the above part numbers was overall height which was very little between all of them.
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Unread 04-15-2013, 11:44 PM   #14
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If anyone else wants to try this on a 4L engine, I predict you'll gain about 1 to 2 mpg in Winter, if you have mechanical fan; or 2 to 3 mpg in Winter, if you have one mechanical and one electric fan; or 3 to 4 mpg in Winter if you have all electric fan(s).

There would be mpg gain in Fall, Winter, and Spring, especially Winter.

No change in Summer since it'd be at same temps range in Summer as stock.

A cold air intake would also help.

Ideal setup for efficiency year round is hot engine, cold intake air, and electric fan(s) that only comes on when needed (214F to 216F engine temp) on hot Summer days.

Even without a cold air intake, running between 205F to 215F is most efficient.

The only way to keep engine at full op temp (range of 205F to 215F) in Winter is 205F thermostat and electric engine fan(s). This setup typically runs around 205F to 210F in Fall, Winter, and Spring. In summer between 205F and 215F. i.e. - perfect temp ranges for efficiency.

The Summer engine temps aren't really any different than stock, but the rest of the year engine is warmer, more like it is in Summer. You get more gas mileage in Fall, Winter, and Spring, and cleaner sparkplugs, valves, and motor oil stays clean much longer.

This is exactly how new cars get better gas mileage.

With these mods you can get surprisingly good mpg (for a 4L Jeep). Especially if you run skinny tires. I run 30x9.5R15.
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Unread 04-16-2013, 02:02 PM   #15
Charley3
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Quote:
Originally Posted by jnicewan View Post
You can research it yourself, I did a little google-fu for ya out of curiosity. In fact on the RockAuto site it lists the A/C Delco as a match for Jeeps, but the thermostat Jeep uses is used in many GM and Ford apps too.

205 stats are hard to find and/or get info on, probably because most of them never had an OEM application. Either match it up at the parts house or compare the dimensions online, the most I saw different on the above part numbers was overall height which was very little between all of them.
Thanks a bunch!

I'll use that info to find em at auto store and then physically compare them.

I'm excited! I love cheap, easy mods that work!
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