Engine Bad radiator cap?

91GTstroked

15 Year Member

Jun 14, 2007

503

281

93

Nov 27, 2021

#1

• Nov 27, 2021

• #1

Hey guy,

First hiccup with my new 93 mustang. Previous owner said coolant was low. And he said that he believes he overfilled the reservoir. Which it is. It is past the hot mark when the engine is cold.

So I let the car sit overnight and take the radiator cap off. It still has pressure and leaks coolant all over.

I believe the cap is the culprit. That valve at the end just dangles. It should be spring loaded correct?

I also can't figure out why they used red coolant? Unless it's that dirty, but it looks more red than brown.

Below is a picture.

Thanks!

 

Attachments

• IMG_20211127_064637949.webp

  99.8 KB · Views: 320

KRUISR

10 Year Member

Apr 16, 2015

1,804

903

143

Nov 27, 2021

#2

• Nov 27, 2021

• #2

That lowest disc I believe is to allow coolant from overflow back into rad. I would replace the cap if it is in any doubt.

Then to get the coolant level right, I start the engine and let it idle and warm it up (with the cap off) until the coolant starts flowing out of the cooling tubes. The coolant level in rad should drop half way or more in the rad tank. Start topping it up until it fills and keeps rad full. After a while, with the engine still running, the coolant will want to burb out of rad. This is when I put the cap back on. At this time I usually fill the overflow to the cold full level and call it a day.

 

General karthief

wonder how much it would cost to ship you a pair

5 Year Member

Aug 25, 2016

27,868

10,542

203

polk county florida

Nov 27, 2021

#3

• Nov 27, 2021

• #3

If there is pressure when opening the cap I'd say it works can't tell what is loose.
Red coolant??
GM used a red coolant, I wouldn't use it, the guys at the shop btched about it alot.
Of course we need a pic, by we I mean me

 

90sickfox

Wasn't a pretty sight...and I've got big hands

SN Certified Technician

Mar 2, 2015

6,945

5,816

213

Nov 27, 2021

#4

• Nov 27, 2021

• #4

A cold system shouldn't have any pressure. When the system heats up the valve in the cap allows coolant to overflow into the bottle. As it cools down that valve is supposed to allow the coolant to pull from the bottle and into the radiator.

Radiator caps are cheap. I prefer the lever vent ones by Stant. It's got a red lever so if it hot you can flip that lever and bleed the pressure out before opening the radiator.

 

Reactions: General karthief

KRUISR

10 Year Member

Apr 16, 2015

1,804

903

143

Nov 27, 2021

#5

• Nov 27, 2021

• #5

Could the pressure you are seeing when the car is cold be vacuum as opposed to pressure? That would mean your system is not allowing the coolant from overflow bottle back into rad. Replace the cap.

 

Reactions: General karthief

91GTstroked

15 Year Member

Jun 14, 2007

503

281

93

Nov 27, 2021

#6

• Nov 27, 2021

• #6

KRUISR said:

Could the pressure you are seeing when the car is cold be vacuum as opposed to pressure? That would mean your system is not allowing the coolant from overflow bottle back into rad. Replace the cap.

Click to expand...

Possibly. Hard to tell, both the radiator and overflow tank were full. But previous owner added fluid.

I'll buy another cap, but I forgot I can use the cap off my 90 coupe and test it. I know that cap works.

 

Last edited: Nov 27, 2021

Reactions: General karthief

91GTstroked

15 Year Member

Jun 14, 2007

503

281

93

Nov 28, 2021

#7

• Nov 28, 2021

• #7

Update:

I put a new radiator cap on, seems to be working. Unfortunately, now I might have a leak at the water pump gasket. I suspect to much pressure in the radiator and it caused a leak at the weakest place.

The whole radiator needs a flush. I'll basically be getting all the fluids changed.

 

Reactions: 90sickfox