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

5.0 cooling system problems

  • Thread starter Thread starter yukonstang
  • Start date Start date Apr 21, 2011
Y

yukonstang

New Member
Apr 13, 2009
11
0
0
Apr 21, 2011
#1
  • Apr 21, 2011
  • #1
i found a 5.0 when i was looking for transmission for my 2.3L. Needless to say i bought it because it was dirt cheap. This car had been sitting for five some odd years and had a broken window so i just swapped the interior due to black mold. I did a few other things, put a new fuel pump in, a new thermostat and thermostat housing, i also changed all the fluids in the car. the reason i changed the thermostat housing was because the previous on was warped and didn't seal, it was crome colored and cheap so im assuming the previous owner bought it from canadian tire or something. The car seems to have a loss of power when i step on the throttle but only when it is hot. at first i assumed it was because of bad gas from sitting for so long but now realize it is from to much heat. Now today the cars cooling system has started pressuring up and building too much pressure and sending all of the the coolant into thye overflow until it leaks it out. it is not just a little leak either it pours out almost a gallon jug then the coolant is too low in the rad. We took it into our shop pulled the plugs checked them and also put pressure into the system (leak down test) assuming it was combustion air leaking into the cooling system but still nothing. The water pump seems to be pumping also. So i come here to find out what you guys figure. Possibly an airlock? how about a plugged up radiator? Post what your take is on this, thanks guys
 

1bad67sbf

Active Member
Nov 24, 2010
674
1
29
N. VA
Apr 21, 2011
#2
  • Apr 21, 2011
  • #2
so you did do a leak down and all cylinders passed? sounds like a head gasket letting blowby go into the water passage or a cracked head maybe. just my thoughts
 

f8tlfiveo

My wife likes my spool and blow-off valve.
Aug 8, 2007
1,585
102
64
Lancaster, PA
Apr 21, 2011
#3
  • Apr 21, 2011
  • #3
+1 on that
 

Rick 91GT

Mustang Master
Nov 29, 1999
9,692
95
99
PA
Apr 21, 2011
#4
  • Apr 21, 2011
  • #4
Air can be a pain to get out of a fox, jack up the front end while starting leave the cap off to help get the air burped.

Are you sure the thermos ta t is opening

Are u sure
 

wiski

Member
Jun 24, 2003
68
0
6
Pittsburg, CA
Apr 21, 2011
#5
  • Apr 21, 2011
  • #5
I've never had problems getting air out of my cooling system. I just start the cold car and run it for a few minutes with the radiator cap off, topping off as needed. As for a blocked radiator; its possible; how did the old coolant look when you drained the car? I'd be more concerned about your t-stat though. I'm with Rick91GT, are you sure its opening? Did you put it in correctly? I've put them in backwards (don't work on your car while tired.) Do you have an electric water pump? If so are you sure its working?

One way to tell if coolant is flowing through your engine is to (using gloves cuz it can get HOT) squeeze the upper radiator hose when the car is running at normal temps. When you release the hose you should feel a surge of coolant flowing through the pipe.

Good luck. I battled with cooling problems with my 5.0 and finally swapped out the black"tragic" 5.0 fan for a nicer electric model.
 

tmoss

Gettin Wired
Founding Member
Jun 28, 2001
7,153
32
128
Saint Louis, MO
Apr 24, 2011
#6
  • Apr 24, 2011
  • #6
good chance he put the t-stat in backwards. The sensor "bulb" need to go on the engine side.
 
You must log in or register to reply here.

Similar threads

M
Electrical 93 5.0 No Injector Pulse
  • machinermac
  • Jul 26, 2026
  • Fox 5.0 Mustang Tech
Replies
15
Views
210
Fox 5.0 Mustang Tech Aug 1, 2026
Willybill32
K
86 GT Water Pump
  • Kade5114
  • May 11, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
3
Views
101
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- May 11, 2026
nickyb
Fox Help
  • 93fox85
  • Mar 22, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
5
Views
223
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Mar 23, 2026
Noobz347
A
1987 5.0 speed density Foxbody crank no start
  • Alan2204
  • May 23, 2026
  • Fox 5.0 Mustang Tech
Replies
10
Views
317
Fox 5.0 Mustang Tech May 30, 2026
Mcmahst
S
Fuel ‘88 GT Runs Rich Cold — Fixes Itself When I Unplug Sensors (ECT, MAF, O2, etc.)
  • Sufarry
  • Nov 6, 2025
  • Fox 5.0 Mustang Tech
Replies
12
Views
883
Fox 5.0 Mustang Tech Nov 9, 2025
Mustang5L5
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?