74 Grand Prix radiator level

Oliverd642

New member
28
0
1
Hello! I’m new to old cars and struggling to find the information I need.

Where should the coolant level be in the radiator on a cold engine? (400motor)

Someone has added a kind of “overflow” tank to my car I guess so excess coolant doesn’t just fall on the floor.. I will fill the radiator up to the neck, after driving and letting it cool completely the coolant level will be around 3/4 up the radiator and the rest will be in the tank, I pour what’s in the tank into the radiator and the same happens again, is this normal? What should the level be on a vehicle that doesn’t come with an overflow tank?
 

melsg5

Staff member
SUSTAINING MEMBER
21,089
172
63
4 PSI is that a typo and it says 14 PSI?
You should have a 16 PSI cap that has a seal around the outer perimeter see the example cap below, look at the picture showing the bottom of the cap .
The overflow from the radiator neck should flow to the bottom of the tank so that as the engine cools it can be sucked back in.
The radiator when fully cold should be filled to the top.
 

Oliverd642

New member
28
0
1
4 PSI is that a typo and it says 14 PSI?
You should have a 16 PSI cap that has a seal around the outer perimeter see the example cap below, look at the picture showing the bottom of the cap .
The overflow from the radiator neck should flow to the bottom of the tank so that as the engine cools it can be sucked back in.
The radiator when fully cold should be filled to the top.
It might be my eyes.. but I’m pretty sure it said 4psi. So these cars are supposed to have an overflow tank? Mine has an aftermarket tank just kind of laying there behind the headlight with the tube from the filler neck of the radiator going into it. The radiator is always 3/4 full when fully cold, each morning I pour the coolant from the loose tank back into the radiator.
______________________________
 

melsg5

Staff member
SUSTAINING MEMBER
21,089
172
63
Look at the engine compartment picture in this link. You can see the tank next to the radiator. It goes to the top of the tank and there is a hose inside that goes down to the bottom to suck the fluid back in when cold.
I explained to you above how it is supposed to work with the correct cap, 16 psi, and the correct tank.
 

Oliverd642

New member
28
0
1
Look at the engine compartment picture in this link. You can see the tank next to the radiator. It goes to the top of the tank and there is a hose inside that goes down to the bottom to suck the fluid back in when cold.
I explained to you above how it is supposed to work with the correct cap, 16 psi, and the correct tank.
Ahh right, I see and understand now. Wow what a great looking GP.

So it’s possible for me to properly mount the aftermarket tank I have, modify the cap so the overflow pipe goes into the cap and to the bottom of the tank? That should work right?

The tank I have, the pipe goes to the bottom of the tank, none at the top. Would it also work if I got proper fittings and fit the overflow pipe at the bottom
Of the tank? Or does it have to go from the top?

Also, is it supposed a pressurized tank or not?
 
Last edited:

melsg5

Staff member
SUSTAINING MEMBER
21,089
172
63
The tank is not supposed to be pressurized.
It is common for aftermarket tanks to run to the bottom.
Not sure what you are trying to modify regarding the cap, do you have type of cap I provided the link to?
It would be a lot easier if you posted clear pictures of the top and bottom of the cap you are using and pictures of the tank.
 

Oliverd642

New member
28
0
1
The tank is not supposed to be pressurized.
It is common for aftermarket tanks to run to the bottom.
Not sure what you are trying to modify regarding the cap, do you have type of cap I provided the link to?
It would be a lot easier if you posted clear pictures of the top and bottom of the cap you are using and pictures of the tank.
Hello again! I just got finished with fitting the tank, replacing the cap and so on. I purchased a 16psi cap. My eyes didn’t deceive me.. the cap on the rad was really 4psi only!? Don’t have time to drive it and see how it goes until tomorrow but here are a few pictures.
______________________________
 

Attachments

melsg5

Staff member
SUSTAINING MEMBER
21,089
172
63
Wow, that cap psi is incredible.
Hope they weren't covering something up by running such a low pressure.
As long as tank has a vented screw on cap you should be fine.
If not vented drill a very small hole 1/16.
Does the new cap have a full rubber seal on the bottom?
 

Oliverd642

New member
28
0
1
Wow, that cap psi is incredible.
Hope they weren't covering something up by running such a low pressure.
As long as tank has a vented screw on cap you should be fine.
If not vented drill a very small hole 1/16.
Does the new cap have a full rubber seal on the bottom?
Hi yes, the new cap as a full rubber seal. The cap on the tank I’m using also has a rubber seal, I suppose I better drill a small hole in it. What could they have been trying to cover if the previous owner purposely bought a 4Psi cap? I drove it to work this morning with no problems (none that I could notice) I do not have a temperature gauge. Maybe I should get myself an aftermarket one.
 

melsg5

Staff member
SUSTAINING MEMBER
21,089
172
63
Typically you run a lower pressure cap when you make a repair to something like a radiator and you have doubts about the quality of the repair.
Just keep an eye on the tank fluid level.
When totally cold the radiator should be totally full and the tank about 1/4 full.
 

Oliverd642

New member
28
0
1
Typically you run a lower pressure cap when you make a repair to something like a radiator and you have doubts about the quality of the repair.
Just keep an eye on the tank fluid level.
When totally cold the radiator should be totally full and the tank about 1/4 full.
Right, okey. Thanks for the help. I drove on the highway today and I noticed a slight leak from under the upper radiator hose. It did leak very slightly from the same place before. I’m going to replace the hoses anyway so I’ll check the neck. Is there any downside to running a low pressure cap? It did fine with it for several hundred miles.
______________________________
 

melsg5

Staff member
SUSTAINING MEMBER
21,089
172
63
The 4 PSI cap creates a very low boiling point which causes the system to eject the coolant from the radiator.
If you see a crack in the neck the best is to repair the radiator.
The next best thing is the chemicals such as Bars Stop Leak.
 
Top