• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

Car Won't Get Up To Operating Temp

  • Thread starter Thread starter AdrianM
  • Start date Start date Sep 13, 2015
  • Tags Tags
    fox body mustang radiator temperature thermostat water pump
A

AdrianM

New Member
Sep 13, 2015
5
0
1
Sep 13, 2015
#1
  • Sep 13, 2015
  • #1
im not really sure where to go from this point so i decided why not give this a try, maybe someone might have a clever idea. i have an 83 fox that i just put a new 2 core aluminum rad in as well as a new water pump. the motor is a carbureted 306 with a comp cam edelbrock heads an edelbrock intake and a holley spread bore. before the aluminum rad and water pump i had an stock 2 core radiator and a new water pump that was spinning the wrong way (the guys before me put a reverse rotation pump on a v belt system lol) anyways, i can't get the car up to temp and I'm not really sure where to go from here. at idle it'll eventually get up there but driving around it just won't. is it possible the rad is cooling too much? do i need a thermostat with a higher rating? mines rated at 180 degrees right now, and it was new about two months or so ago. I'm just not sure where to go from here.
 

CarMichael Angelo

my rearend will smell so minty fresh,
15 Year Member
Nov 29, 1999
10,641
8,909
234
Birmingham, al
Sep 13, 2015
#2
  • Sep 13, 2015
  • #2
AdrianM said:
im not really sure where to go from this point so i decided why not give this a try, maybe someone might have a clever idea. i have an 83 fox that i just put a new 2 core aluminum rad in as well as a new water pump. the motor is a carbureted 306 with a comp cam edelbrock heads an edelbrock intake and a holley spread bore. before the aluminum rad and water pump i had an stock 2 core radiator and a new water pump that was spinning the wrong way (the guys before me put a reverse rotation pump on a v belt system lol) anyways, i can't get the car up to temp and I'm not really sure where to go from here. at idle it'll eventually get up there but driving around it just won't. is it possible the rad is cooling too much? do i need a thermostat with a higher rating? mines rated at 180 degrees right now, and it was new about two months or so ago. I'm just not sure where to go from here.
Click to expand...

More than likely, your new thermostat is stuck open. Replace it w/ a new one, and you'll probably be good to go.
 

7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
7,387
2,745
194
Kearney, NE
Sep 13, 2015
#3
  • Sep 13, 2015
  • #3
If that does not do it, what gauge are you using? Cleaning the connectors at the sender changed the reading range in my dash, and a poor ground can peg all of them out. I hope Someone has posted the right multi meter readings.

To check out if the reading is close, you can use an infrared thermometer, a candy/cooking thermometer actually in the radiator, or a mechanical gauge. If you use your meat thermometer, remove the radiator cap cold so you do not get sprayed with hot antifreeze! You should be able to see a big difference in flow from a closed thermostat to when it opens up at temp.
 

7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
7,387
2,745
194
Kearney, NE
Sep 13, 2015
#4
  • Sep 13, 2015
  • #4
I like the balanced flow design thermostats like the picture. Robert Shaw sold them first in the area, but I see others copy or repackage them. It is supposed to have better open flow and not close under high RPM.
 
A

AdrianM

New Member
Sep 13, 2015
5
0
1
Sep 13, 2015
#5
  • Sep 13, 2015
  • #5
madmike1157 said:
More than likely, your new thermostat is stuck open. Replace it w/ a new one, and you'll probably be good to go.
Click to expand...

ill give this a try, i have a 180 but i think i might go to a 195 now that i have a bigger radiator it can handle a little more heat.
 
A

AdrianM

New Member
Sep 13, 2015
5
0
1
Sep 13, 2015
#6
  • Sep 13, 2015
  • #6
7991LXnSHO said:
If that does not do it, what gauge are you using? Cleaning the connectors at the sender changed the reading range in my dash, and a poor ground can peg all of them out. I hope Someone has posted the right multi meter readings.

To check out if the reading is close, you can use an infrared thermometer, a candy/cooking thermometer actually in the radiator, or a mechanical gauge. If you use your meat thermometer, remove the radiator cap cold so you do not get sprayed with hot antifreeze! You should be able to see a big difference in flow from a closed thermostat to when it opens up at temp.
Click to expand...

i have an new autometer sort comp 2 water gauge. i know it works and i know its accurate cause I've used one of those laser temp guns and its showed the same temp.
 

7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
7,387
2,745
194
Kearney, NE
Sep 14, 2015
#7
  • Sep 14, 2015
  • #7
Your computer (unless tuned) will appreciate the factory rated thermostat. I am not sure it will go into closed loop with the cooler one, especially if the thermostat is not working.
 

stykthyn

I want to measure mine. It doesn't look that tall.
15 Year Member
Jul 6, 2006
5,232
2,652
223
gainesville
Sep 14, 2015
#8
  • Sep 14, 2015
  • #8
Carb motor no computer, but still, I would think that the 195 is the way to go. If you're really hung up on your tstat you can put it in a pot of hot water abd verify it opens up but honestly by the time you've done that you may as well have purchased a new one.
 
Reactions: a91what

stang89bidges

Advanced Member
Mar 14, 2014
727
144
74
Fort Worth Texas
Sep 14, 2015
#9
  • Sep 14, 2015
  • #9
Just curious, why the 195° the way to go? Heat transfer better or something else? Been doing a lot of research into this and like to hear others opinions.
 
A

AdrianM

New Member
Sep 13, 2015
5
0
1
Sep 15, 2015
#10
  • Sep 15, 2015
  • #10
I put in the new 197(lol Ford) degree thermostat I got right from the Ford dealership. Costed me 27 bucks...yay canadian prices But it seems to be working so far. I didn't get much driving in today as I only went a distance but it got up higher than it has since the new rad/ water pump etc. I think my old thermostat was opening too soon, I guess that's what happens when you buy a quality part compared to a 6 dollar thermostat. I'm gonna check back in a couple days to confirm its fixed
 
A

AdrianM

New Member
Sep 13, 2015
5
0
1
Sep 15, 2015
#11
  • Sep 15, 2015
  • #11
stang89bidges said:
Just curious, why the 195° the way to go? Heat transfer better or something else? Been doing a lot of research into this and like to hear others opinions.
Click to expand...

Higher temp your motor is running at means the fuel is burning a little more efficiently = better mpg and better emissions, but if your motor runs a little cooler I believe you have a little bit more power. That's just my two cents anyways. It doesn't matter to me if a lose a couple ponies as long as my car is running good and I don't have any issues
 
You must log in or register to reply here.

Similar threads

Engine Themostat
  • Mindseye007
  • Jan 30, 2026
  • Fox 5.0 Mustang Tech
  • 2
Replies
21
Views
698
Fox 5.0 Mustang Tech Feb 1, 2026
86HO5.0
8
K
86 GT Water Pump
  • Kade5114
  • May 11, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
3
Views
83
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- May 11, 2026
nickyb
9
Engine Donor '00 Mountaineer meet '91 Fox
  • 91firecracker
  • May 11, 2026
  • Fox 5.0 Mustang Tech
  • 2 3
Replies
41
Views
792
Fox 5.0 Mustang Tech May 28, 2026
91firecracker
9
W
High Cylinder Head Temp - Not Overheating?
  • wtfwork12
  • Jun 26, 2025
  • 2005 - 2014 S-197 Mustang -General/Talk-
Replies
9
Views
2K
2005 - 2014 S-197 Mustang -General/Talk- Jul 1, 2025
wtfwork12
W
6
Hey all,I’m putting together a 302 for my 1968 Mustang and wanted to post the combo + some questions to make sure I’m not missing crucial
  • 68_Disgustang
  • Feb 22, 2026
  • 1965 - 1973 Classic Mustangs -General/Talk-
Replies
4
Views
801
1965 - 1973 Classic Mustangs -General/Talk- Jun 20, 2026
gray owl
G
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?