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  1. #1

    Default 205 Degree Thermostat?

    So, I'm given to understand that SEFI engines operate most efficiently at temps around 205-210. In an effort to get myself closer to that, I am running a 190 thermostat. My stupid engine never gets above 180-185. I have my fan set to come on at 205, and the thing hardly ever runs! I've also come to learn my understanding of how a thermostat affects your engine temp is a bit off in thinking it will run warmer than the thermostat open temp. Educate me, please.

    Second problem. If I were to go to a higher temp thermostat, where would i get it? The highest temp one I can find is 197.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  2. #2
    FEP Super Member gr79's Avatar
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    Anything to get it at least to the 190's
    T-stat too. OEM 192-195 spec close enough.
    One that works properly is key.

    Temp. block off some of the radiator?
    Or set the fan sensor trip a little higher.
    Prob would run hot if 1/2 rad was blocked off.

  3. #3

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    First of all, you live in Shakopee... You have like two months a year above freezing...
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, catted BBK H-pipe, full custom duals. 3.73 rear. CS5 225/60/15 on 10 holes.
    Everything else stock and fully functional.

  4. #4
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    I'm running a A9L EEC,so when temperature gets to 190°F the A9L EEC pulls 2° of timing, so a 180°F thermostat is probably the best performance choice but maybe not the most efficient.

    www.veryuseful.com/mustang/tech/engine/EECIVInnerWorkings/
    '86 Med.Canyon Red Met.(original paint) T-top,5 speed,3.55 rear,MAF conversion(A9L).MM adj. RLCAs,T/A,Panhard Bar,and adj MMRSB-3,rear T/A springs 375#-440#,MM C/C plates,MM 1.125" dia.swaybar,STB,4pt KMB,FLSFC's,'03 Cobra rack-n-pinion w/ Saginaw pump conversion.Bilstein MM coilover conversion and A-arms,front spring rate:250#.

  5. #5

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    Quote Originally Posted by OldManRiver View Post
    I'm running a A9L EEC,so when temperature gets to 190°F the A9L EEC pulls 2° of timing, so a 180°F thermostat is probably the best performance choice but maybe not the most efficient.

    www.veryuseful.com/mustang/tech/engine/EECIVInnerWorkings/
    That's interesting, I had no idea! Maybe I'll just stop thinking about it! I'll probably slap a Motorcraft 195 in my new engine when it shows up. Summit has those.

    Here in MN, we have what's called "continental climate". That means it gets colder than anywhere else, yes, but it also means it gets HOT. From late June to mid-August, we get some seriously hot weather. Humid too, so worse than the desert. What do you think makes all those tornadoes? We have the widest range of temps in the country.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  6. #6
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    The thermostat sets the minimum engine temp more often than the maximum, which is governed by the cooling capacity of the radiator, cooling fan, air flow, etc. (An engine which overheats with a 190* thermostat will overheat just as badly with a 160* thermostat, assuming equal flow through both. The temp of the coolant hitting the radiator would be the same after a very short time.)

    Except for very low ambient temperture conditions, like where ZephyrEFI lives. 70's Ford pickups with the 300-6 would freeze you in the winters here without the radiator being partially blocked.

    Edit for clarity and grammar.
    Last edited by darkd0r; 07-07-2018 at 04:52 AM.

  7. #7
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    Another thought or two, perhaps more to the point.

    1. Is your temperature gauge accurate? If you're only getting to 185*, the 205* fan should never come on.

    2. Is the fan switch actuating temperature accurate? You might disable the fan entirely for a test.

    3. Have you tested your thermostat to check if it really opens at 190*? Considering the quality of parts these days.

    4. What is the ambient temperature when you hit 185*?

  8. #8

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    I started really noticing this odd behavior when I went to install my A/C system. That happened to coincide with installing a new aluminum radiator. Just thought I should note that.

    Temp gauge is just the factory one, so who knows if it's accurate. I've often considered adding a small aftermarket one under the hood somewhere. Maybe when I have the engine out that will be a good time to do that.

    No, I haven't actually tested temps in comparison to thermostat opening or the fan turning on. I do have a cool laser thermometer to play with though.

    The thermostat that's in there (if I'm right) is a Motorcraft, but it's been through an overheating so who knows if it's working right. It does open though, I know that.

    I haven't tested the fan switch compared to actual temp either.

    Ambient temp has been mid '70s mostly. The real test will come for Street Machine Nationals. It's always hot as hell for that.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  9. #9
    FEP Senior Member Matt J's Avatar
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    I'd definitely add an aftermarket temp gauge, I like the cheapo sunpro mechanical deal you can get at any auto parts store for about 20 bucks. You can run the sender through the existing holes in the firewall, and I mounted mine temporarily under the dashboard on the passenger side of the console. I just clipped it to the bottom of the dash hull with a big paper clamp. You need to get a number to what temp it's running so you can see when the thermostat opens, when the fan comes on, etc. It works a lot better to do it when you're actually driving it without having to get out and check the temps with a handheld thermostat. You might find out that you don't actually have a problem, if the car is otherwise running well.

    If it's already got a 195 in it, assuming that it's working correctly, then if the temp only gets up to 185 it won't open anyway; it would only open at that base rated temp. Same would go for one rated at 205. If your engine is set up stock I'd definitely run the one that's proper for your engine. These cars had different thermostats in different years and for different setups. My 84 with CFI called for a 195 as I recall. Others call for a cooler one.

  10. #10

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    Quote Originally Posted by emerygt350 View Post
    First of all, you live in Shakopee... You have like two months a year above freezing...
    Too Funny!
    Project "WinBacK" 1986 LX Hatchback
    - CA car, 5.0 w/5 speed
    -Cheap 5 Lug Swap w/Cobra 17x8.5's + Modded Mach1 Chin Spoiler + 83-84 Hood & Scoop/85-86 "Blackout"+ FMS Mass Air Kit+ MM Clutch Cable & Quadrant + Fiore Cable Adjuster + MM SFC's+ Wild Rides "Battle Boxes" + Explorer Intake, Converted TB & Injectors, 70 mm Mass Air Meter + BBK Ceramic Shorties + 2.5" Bassani O/R X-Pipe & Cat-Back Exhaust w/ 3" Tips + 3L27 w/ Carbon Fiber Clutches​(out of retirement) + Pistol Grip Shifter

  11. #11

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    I've got an old 4 core BBK radiator circa 1994 and a Motorcraft 195° thermostat in the '86 and the running temp seems fine no matter how hot the ambient temp is.
    Project "WinBacK" 1986 LX Hatchback
    - CA car, 5.0 w/5 speed
    -Cheap 5 Lug Swap w/Cobra 17x8.5's + Modded Mach1 Chin Spoiler + 83-84 Hood & Scoop/85-86 "Blackout"+ FMS Mass Air Kit+ MM Clutch Cable & Quadrant + Fiore Cable Adjuster + MM SFC's+ Wild Rides "Battle Boxes" + Explorer Intake, Converted TB & Injectors, 70 mm Mass Air Meter + BBK Ceramic Shorties + 2.5" Bassani O/R X-Pipe & Cat-Back Exhaust w/ 3" Tips + 3L27 w/ Carbon Fiber Clutches​(out of retirement) + Pistol Grip Shifter

  12. #12

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    Quote Originally Posted by Matt J View Post
    I'd definitely add an aftermarket temp gauge, I like the cheapo sunpro mechanical deal you can get at any auto parts store for about 20 bucks. You can run the sender through the existing holes in the firewall, and I mounted mine temporarily under the dashboard on the passenger side of the console. I just clipped it to the bottom of the dash hull with a big paper clamp. You need to get a number to what temp it's running so you can see when the thermostat opens, when the fan comes on, etc. It works a lot better to do it when you're actually driving it without having to get out and check the temps with a handheld thermostat. You might find out that you don't actually have a problem, if the car is otherwise running well.

    If it's already got a 195 in it, assuming that it's working correctly, then if the temp only gets up to 185 it won't open anyway; it would only open at that base rated temp. Same would go for one rated at 205. If your engine is set up stock I'd definitely run the one that's proper for your engine. These cars had different thermostats in different years and for different setups. My 84 with CFI called for a 195 as I recall. Others call for a cooler one.
    The only receipt for a thermostat I can find says that I have a 190. And it IS opening, so 185 might be a little off for the actual temp the engine runs.

    When I have my engine apart coming up, I will add another temp gauge. The main thing stopping me until now was having to drill into the water jacket for the sender.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  13. #13

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    Quote Originally Posted by banzaibullitt View Post
    I've got an old 4 core BBK radiator circa 1994 and a Motorcraft 195° thermostat in the '86 and the running temp seems fine no matter how hot the ambient temp is.
    Good to hear. I think you might live in a similar climate.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  14. #14

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    I was looking at one of those radiator caps that has the gauge built in. Pretty slick. But... of course it's not as simple as grabbing one that fits a Mustang. The SVE radiator has a different size cap THIS IS WHY I DON'T LIKE TO DEVIATE TOO FAR FROM STOCK!!
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  15. #15
    FEP Senior Member Matt J's Avatar
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    If you buy one from the parts store, it will have its own sender, it simply screws in where the electric sender for the stock gauge is. I took my stock sender out, but kept it so I could plug in the original later if I chose to, and screwed the new one in its place. No need for drilling!

  16. #16

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    Oh, yeah, I suppose no need for both.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  17. #17
    FEP Supporter 4-barrel Mike's Avatar
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    Quote Originally Posted by ZephyrEFI View Post
    THIS IS WHY I DON'T LIKE TO DEVIATE TOO FAR FROM STOCK!!
    WAY to late to worry about this!

    Mike
    1985 ascMcLaren 5.0 SC Roadster
    My '78 Fairmont build - http://vb.foureyedpride.com/showthre...539-78-Big-Red

  18. #18
    FEP Super Member gr79's Avatar
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    Drill into the water jacket? Wow.
    Easier way is to tee sender off existing temp sender.
    Or add a tee in a heater hose.

    Have teed oil pressure with iron pipe fittings from big box home stores.
    Do not use brass pipe. It cracks. Brass tee part ok but more costly than iron.

    On my Ranger, have mechanical temp gauge teed directly to heater hose.
    No cutting. Is active all the time as would be in block.
    Removed heater core inlet hose from existing tee (factory sensor on KT-82).
    Added 2nd tee. OE spring clamps work fine. Worm clamps dig into rubber.
    Completed hose routing by adding a new section of heater hose from tee to tee.
    Been working perfectly for 20 years.
    The tee is a Motorcraft KT82/F2TZ18B402A HVAC Heater Pipe from Rock Auto.
    Is little costly, but paid for itself many times as part of the temp gauge package.
    Can be found on salvage yard 92-97 Ranger 2.3.
    Mech temp gauge kit sending tube connects gauge to the tee.

    Name:  heater tee KT82.jpg
Views: 108
Size:  121.8 KB

    Reference only no endorsement of Amazon:
    https://www.amazon.com/Motorcraft-KT.../dp/B00809UQ48

  19. #19

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    Quote Originally Posted by 4-barrel Mike View Post
    WAY to late to worry about this!

    Mike
    Well, you know what I mean. Stock SOMETHING. Certainly not Zephyr though.

    GR, good idea. Only problem with that is, my heater hoses are the VERY short SEFI engine style. Made even shorter when I moved the engine back. Not much room for a tee in those. Might be able to find a place though!
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  20. #20
    FEP Super Member gr79's Avatar
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    Extend (add) hose? A longer loop.
    Route new longer hose to accessible area, install tee.
    Make it pretty.

    Seeing the factory one already there gave me the idea.
    And since its a PCM temp sensor, figured water temp would be accurate enough in the hose for the mech gauge.
    And it is. The water is always circulating there, even when t-stat is closed. Using heater hose circuit works.
    Was hard to find out what the tee's number was and even what it was called.
    My mod on the truck is reversible if anything happened.
    Remove added tee and short hose 'bridge', reconnect heater hose to oe sensor where it was.
    Last edited by gr79; 07-08-2018 at 05:05 PM.

  21. #21

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    Quote Originally Posted by gr79 View Post
    Extend (add) hose? A longer loop.
    Route new longer hose to accessible area, install tee.
    Make it pretty.

    Seeing the factory one already there gave me the idea.
    And since its a PCM temp sensor, figured water temp would be accurate enough in the hose for the mech gauge.
    And it is. The water is always circulating there, even when t-stat is closed. Using heater hose circuit works.
    Was hard to find out what the tee's number was and even what it was called.
    My mod on the truck is reversible if anything happened.
    Remove added tee and short hose 'bridge', reconnect heater hose to oe sensor where it was.
    Thanks for digging that up! I was looking at the engine and the hose that goes from the water pump to the heater hose pipe is plenty long and could be used for this.

    I was looking at thermostats around the web, and it appears that the thermostat I have in mine is the OE recommended one. It's listed as both 190 and 192. It has 192 stamped right on it though. I do not see a Motorcraft one anywhere with a temp of 195 except for different applications. I think I might go to a different brand for that reason just to see if I can get my operating temp up a bit. Anyone have experience with a Stant "Superstat" of a Motorad "Failsafe"? They both have gimmicks, so that turns me off about them, I guess. If I can't use a fairly pricey Motorcraft, I guess I gravitated to these brands' more expensive lines.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  22. #22
    FEP Senior Member
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    Robert Shaw should make a 195* t-stat.

    Does your t-stat housing have a boss you can drill and tap? I think most do.
    I installed the factory sender there so not to have a dead gauge in the cluster after installing an aftermarket gauge sender in the stock location.
    '86 Med.Canyon Red Met.(original paint) T-top,5 speed,3.55 rear,MAF conversion(A9L).MM adj. RLCAs,T/A,Panhard Bar,and adj MMRSB-3,rear T/A springs 375#-440#,MM C/C plates,MM 1.125" dia.swaybar,STB,4pt KMB,FLSFC's,'03 Cobra rack-n-pinion w/ Saginaw pump conversion.Bilstein MM coilover conversion and A-arms,front spring rate:250#.

  23. #23
    FEP Super Member gr79's Avatar
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    KT82 installs in 5/8" heater hose. Believe heater outlet hoses to wp are 3/4".

    I see one aftermarket t-housing has a tapped hole with a hex plug.
    https://www.rockauto.com/en/catalog/...r+outlet,10337
    Looking at the sensor section, appears the 5.0 uses same sensor as my 2.3 does in the KT82 tee.
    3/8" pipe thread.
    Assuming that is the same size in the t-housing too.
    Ranger in later years got rid of the tee and installed the temp sensor in the t-stat housg/water outlet.
    Has a tapped hole for it, like the later 5.0 housing has.
    The sensor will install in the tee or housing. Same thread.

    Bought the newer style while back and trial fit a new sensor.
    Am going to move the mech gauge tube or PCM sensor to the hsg.
    Current OE t-housing has seen better days. So have the two KT82's. Bought one new one.

  24. #24

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    Good call on the housing. The boss is there on mine, no threads or plug, but I should have the proper drill and tap around somewhere. It would be funny if I decided to get a new pre-threaded housing just for simplicity because that would be the FOURTH one to go on the car (fifth if you count the one on the original engine). The original broke, then i got a steel one to replace it in a pinch, then that one got all rusty, so i replaced it with a proper aluminum one.

    Okay, if that hose is a different size. I'll measure it though just so we know.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI T-5 (Mustang LWB)
    '17 Ford Transit Connect Titanium LWB
    '14 Ford Fusion SE Manual

  25. #25
    FEP Super Member gr79's Avatar
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    We have the same climate in Detroit= Köppen Classification Dfa. Humid Continental.

    Mech temp gauge on truck yesterday was 185-205. High 80's ambient.
    Autometer/Autogage 2313 shows 185 is in normal zone below the factory gauge N.
    195 is just below or barely on the N. At 200-205, cluster gauge pointer was on the middle of the N.
    200 was trolling thru parking lots or idling. 185-195 would be moving faster.
    Unknown how accurate the mech gauge is but is consistent and no lag. 270° sweep.
    The two temp gauges pretty much follow each other but not always.
    Seem to recall 220-230 had the pointer past the mid point of the stock gauge.

    Now that i look at it, did use an adapter to install gauge capillary tube to fitting.
    Also raises the probe up from the coolant stream instead of blocking it.

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