I recently installed one of the Aluminum Spectra CU165 radiators. All new hoses, new 180* thermostat, and coolant.

It's full, and the car seems to be running at 175/180* all the time(at idle, at 40, at 80mph+).

My problem is, the system doesn't seem to be pressurizing. At first, I thought it was just an air pocket, but the radiator is full, the coolant comes up to temp, but I don't think the cap is sealing on the plastic tank. I've tried two caps, a Mr. Gasket ThermoCap and a Stant Pressure Release Cap. Each cap, when I squeeze the top radiator hose, I can hear air coming out the overflow hose. So I put a plug on the overflow) just to test) and it's still not building pressure.

There are no visable leaks, and the cars runs 180* max all the time. Which, even though it was only 48* ambient today, is really good. I even blocked the grills with cardboard, and the temp didn't rise much at all.

I don't know what to do. The caps are on all the way. The system used to build pressure just fine before the radiator swap.

What am I missing?

 

Get a cooling system pressure tester and figure out where the leak is.

 

X2^^^
I don't think 2 rad caps can be faulty, especially the Stant cap. Even with an air lock it would build pressure, just overheat quicker.

Eric

 

Okay. If it was anywhere other than the cap, anti-freeze would be be leaking, and it's not. I'm going to call Spectra tomorrow when they are open and see if they recommend a specific cap. The neck looks fine, I don't understand why it isn't sealing.

Maybe I'll duck tape the cap hole, and pressure test the system.

 

If its not up to pressure then you wouldn't see the leak I know 200MPH tape works for alot of things but... Stand back if she blows. Ohh, that kinda sounds good!!

Eric

 

If you heat coolant to 180 and its 48 outside, you should see moist at the cap if it is leaking.

 

You could check the depth on the filler neck, check the travel on the cap spring to see if it has the travel to seal, but I doubt that is the problem.

 

Just do like Joe said and test the cooling system and the cap.

Go to any chain auto parts store, "free rent" a pressure tester (pay for it, then they refund you when you bring it back), and test it.

It's the only way you'll know what's going on.

- Eric

 

^^^^ that's a deal ^^^^
Can't beat a free pressure tester to use, they aren't that cheap to buy so if you local parts store lends it out then that's the way to go for sure.
You'll see the problem immediately, no guess work.

Eric

 

Doesn't "seem" to be pressurizing? There are no outward signs that the cooling system is pressurized during normal operation unless you have a gauge somewhere.

Why do you think it is not pressurizing? As noted, if it wasn't, you'd have coolant leaking somewhere.

More importantly, you say that the car seems to be running fine. I guarantee you that if your cooling system were not pressurizing, the car would not be running fine as you sped down the highway at 80 miles per hour.

One of the effects of a pressurized system is an increase in the boiling point of the coolant. If the cooling system were at atmospheric pressure, the coolant would be boiling over, you'd have steam coming out from under the hood, you would have a mess on your hands, and you would definitely know that the system is not pressurized.


This has all the hallmarks of trying to fix something that ain't broken.


I'd be very curious to hear your conversation with Spectra. "My car is running fine with your new radiator installed. Please tell me what's wrong."

 

That's not necessarily true about boiling over. If he is not getting up to 210+ degrees it won't. The added pressure raises the boiling point well above the 210 degrees. Also if he is not building pressure due to a leak in the cap, he may not lose coolant just pressure.

 

If he's going 80 mph, it will get over 210.

He still hasn't given any explanation as to why he thinks the system isn't pressurizing.

 

Are you sure the cap is on all the way, there are 2 positions. First when you turn the cap a partial turn, second when you push down on the cap to turn the rest of the way?

 

There is no valve in the radiator cap that permits only gases or vapors to pass and not liquids.

If the cap is not sealing, there is a pathway for coolant to leak out. It won't leak just sitting there on a cold engine, but at 80 mph, and assuming the coolant level is full, the increase in coolant temperature will cause the level in the radiator to rise and leak out around the cap. That's why we have overflow tanks. The rising level of the coolant passes through the valve in the cap and into the recovery tank.

If he's not seeing evidence of a leak around his radiator cap, there is no reason to suspect the cap.

 

Because the upper radiator hose isn't getting firm/stiff. Before the radiator swap, if I squeezed the radiator hose(after running) it was firm, hard to squeeze. The new one isn't doing that. So the upper radiator hose isn't pressurizing. When I squeeze the upper radiator hose, I can hear air coming out of the overflow nozzle and into the overflow jug.


Yup. On both caps.



I did. It certainly seems like it should be bottoming out.

 

This isn't evidence of anything. You said you also put on new hoses. Hoses get stiff and hard to squeeze as they age. New hoses will in general be easier to squeeze, and at the elevated temperatures an engine operates at, they will become even more pliable. As high as the pressure gets in a cooling system, and it isn't all that high at 15 psig, which is just one atmosphere above ambient, it doesn't get high enough that the radiator hose could still not be compressed with a bit of effort between thumb and fingers.

As I said earlier, I don't believe you actually have a problem. If your only evidence is the easy to squeeze hose, you have no problem at all.

 

I'd say you have an "AIR LOCK" myself.
But that doesn't explain the 80MPH holding 175-180 temps without coolant either pushing out the overflow hose or into an overflow bottle if equipped then spiking your temp , reguardless of your 180 t-stat. Than your upper rad hose would be soft for sure

 

It most certainly doesn't. If he can drive down the highway all day long at 80 mph with no problems, his system is pressurizing regardless of how the hose feels.

 

Ok, it sounds to me as thou the cap was installed to early. The system didn't have time/good enough flow going through the rad allowing the T-stat to open up properly to get the air locks out prior to capping the rad and taking it for a rip. JMO

Eric

 

Jaunty, stop. I'm sorry, but you're wrong.

A properly operating 15-20psi system, once fully warmed up, will have radiator hoses that feel pretty close to rock hard. When cool, they will be soft.

That's just the way it works. It isn't subtle and there's no mistaking it.

His cooling system is not holding pressure. He needs to find out why and fix it.

- Eric

 

No, I'm not. He can drive 80 mph with no problems.

He has yet to present any convincing evidence that he has a cooling system problem.

 

In a closed system such as an overflow bottle which you have, continue to top off the rad once cooled down, you will either
A) find the leak or
B) The system will eventually purge the air out itself.
OR, disregard this and "C" is your best bet to follow up with diagnosis.
C) read post #8 and #2 and at that point follow up with everyone.

 

This is what I thought. Other classiccars in the family, the top radiator hose is hard to squeeze if at all if it's running and warm. Mine used to. It isn't anymore.

No one locally have a coolant pressure tester for rent.
The coolant isn't going anywhere, the level it maintaining. I even added a little to the overflow, just in case.

 

You can't have a leak that looses pressure without also losing coolant. Either there is a leak or there isn't. If the radiator cap were not sealing to the filler neck, then you'd see vapor or steam there at a minimum. I'm still not convinced there is a problem.

 

Did you have heat coming through the defrost when you were almost done filling the rad and just about up to temp.? Do you have heat at the floor vents now?
The reason I ask this question is, you may have an air lock in the heater core or it could possibly be plugged up a bit or a little leak, not getting your system up to proper pressure.
Did you replace your heater hoses? You could have loosened the heater hose pipe, they loosen very easily when changing heater hoses that have been on for years.
Do your heater hoses have pressure?
I hope this helps
Eric

 

My second car, which I drove for ten years, was a 1970 Chevelle SS. Its original 4-core radiator had tanks made of swiss cheese, which I used to patch with pennies on a regular basis. That kept the water inside, and the level would barely ever go down at all, but it never used to make any pressure (there were a few times when it did, but they didn't last long.

No steam, no significant coolant loss, no overheating, ever, but the system would not hold pressure.

I ultimately left that old radiator in a garage when I moved out of a house and was glad to be rid of it. It was only later that I discovered that factory original Chevelle SS 454 radiators are themselves collectible and valuable. Who knew?

- Eric

 

Its possible he has no pressure as well, but good pressure at the hoses once warmed up to proper temperature = good flow .
I like to see good flow after install , working heat through the defrost so I know the thermostat is open and working, water pump is pumping , pressure at all hoses soon after the cap is placed on = good flow throughout the system.

I would be stumped as well with his findings.

Eric

 

I won't be stumped until I know how the pressure test went.

Since it's not my money, I say go ahead and spend the $150 for a new pressure tester. Once you've got one, you won't know how you lived without it.
I got mine at a flea market for $20, but I find it so useful that I've packed it for a trip we're going on - you never know...

- Eric

 

Yes, I agree at this point it would be worth the investment, the tester would nail it down immediately. It could be a small leak at the heater core and may take a few trips to notice the coolant going down. I don't think a call to Spectra will kelp in this case if he's waiting for a diagnosis, unfortunately.
We have helped him as much as we all could, its up to him now.

 

I think Joe and Jaunty have nailed it.
It doesn't overheat, doesn't leak coolant, gets to normal operating temperature.

I wish all my problems were this hard.

Roger.

 

I don't see anti-freeze or vapor. The only thing I can think of, is the cap isn't sealing where the spring/rubber gasket of the cap meet the bottom of the fill neck, but the seal on the cap itself does, so air on constantly spilling into the non-pressurized overflow tank. If I squeeze the top hose, I can hear air going into the overflow.


I do have heat. I only have floor vents for heat. It's as warm as it always is. (not hot compared to new cars, but warm). I did replace the heater hoses, but i cut them off with a razor blade. I went through the hell of replacing the heater core 2 summers ago, I wasn't going to risk breaking the new one.

Again, I hear air going into the overflow tank, as if the spring seal on the caps aren't blocking off that overflow hole.

I'll figure out something about a pressure tester. Even if I have to make one.

 

When you squeeze the top rad hose you will hear air going to the overflow tank, but when the car is up to temperature and the upper rad hose if firm, it will be harder to squeeze when running and shouldn't hear anything.
If their are any air locks they will work themselves out through the overflow, just check your overflow after a few trips and add if needed. If you are sure ther is no leak then you should be good to go.

Eric

 

Sounds like the incorrect rad cap or it's not turned completely to the neck. It needs to be pressed down and turned. It a two step process. Hope this helps.

 

My temp gauge is only reading 175*/180. If the thermostat is a 180* thermostat, I'm not sure it's really up to temp. It should be running slightly higher. I would think. But then again, it is cold out, cold air does help cool an engine.

My upper hose is never getting firm. thats what I noticed and caused me to write this thread.

 

Yes. The caps are put on correctly. Two notches in. This is my thought too. that's why I wanted to call Spectra and Ask about the Correct Radiator Cap. Because it seems like the ones that would fit my Original Radiator, aren't sealing for this new radiator. And I don't know which would be the correct cap.

 

What PSI cap did you buy?

 

16. Same as was on there.

 

That's weird, can you check the depth of the fill cap on your Old rad with the depth on the new plastic tank. Is it much different? Same with the locking lip cap thickness?
Perhaps they put a different plastic tank on by mistake?

 

If its different is 1/16" of an inch. I know that enough, but I can't tell with a tape.

The pressure tester holds pressure in the system, so it's def. the cap not sealing off the bypass, because it's not deep enough into the neck.

I called Spectra and they recommend a stant 10331. That's what I have. I also tried my old ThermoCap which is 2471s. I may try the 10231 which is the non pressure relief lever cap, just to see. The ThermoCap 2470 may fit, but it's not in stock locally.

This just seems silly.

 

Your guesstimate which sounds close,1/16 or .0625 isn't much of a gap, what if you took the rubber gasket out of the top of your old cap and out of one of the 2 news ones you have, also pry the lower gaskets off and put them on the better of the two new caps you bought, I would say the stant.
The lower gaskets will be more difficult to get out, so maybe just use a utility knife and cut them out as close to the centre.
Put them together and add them to the stant cap.
Or try to rig something similar up to get one cap to seal, if you feel the caps are the issue.
This may be a good test to see if it seals better, may be worth a try rad caps are cheap, what do you think, could you rig something up for a test? .
You may want to check it two different ways just thicken the gasket on the bottom, then just on the top, or maybe both at the same time. You will know what may work by how much pressure you need to push and turn the cap on. You may need a little lithium grease so that it slips easily with multiple gaskets without dragging
Eric