7T1vette: Is the thermostat the one which is located below the aux. tank on the hose that goes out of the tank?

Reggie Dunlop: By combustion gases you mean the cylinders blowing pressure to the cooling system = a head gasket problem? I was actually afraid of this before I bought this car and that's why I consulted with a couple of mechanics, including the one who pushed the hose He told that there is no chance of head gasket problems cause the oil is perfectly clean, there is nothing coming out of the exhaust, and I wouldn't have been able to drive around for an hour. He told that in order to break a Chevy 350 cylinder head you'd have to really work hard to achieve it - run the engine at higher RPM without coolant and then fill it with cold water.

Still, what about the radiator cap? Is the 330 lbs correct one? I read in other threads that there are two caps - used with aux. tank systems and without the aux. tank. Perhaps there is a wrong one installed? I don't get it anyway why can't I just have such a radiator cap which releases certain pressure when it goes too high and that's it... I mean, my cap has the manual pressure release handle and if I just release some of it while engine is running, the big radiator hose also goes much softer. Do it automatically and the problem is solved, isn't it?

 

Your radiator cap will release excess pressure on it's own. The handle is for you to manually relieve pressure [for whatever reason]; lifting the handle will vent any pressure so that you can safely remove the cap for adding water/coolant.

 

A few comments:

There's no such things as a 330 lb cap, they're usually 12-16 lbs. Can you post a picture?

No Corvette came with a manual pressure release handle so yours is not original, and may be incorrect.

The cap is designed to release/regulate pressure while the engine is running. The excess coolent flows into the plastic recovery tank under the passenger side fender. No need for you to release it manually. This act is actually conterproductive as the boiling point of the fluid is substantially reduced by lowering the pressure.

 

I took the cap to one of the US car services here and they told it's in just fine condition and should work without any problems. I cleaned it up a bit and found that it's 15 lbs not 330, ofcourse.

I also took the smaller hose off which goes from underneath the radiator cap to the aux. tank. I blew air through it and it seems to be clean. There didn't seem to be any blockage in the aux. tank inlet where the pipe connects.

Can someone please explain me a bit how the radiator cap / aux. tank system works? Is the cap acting like a valve which opens automatically when a certain pressure is reached? Is the coolant sent to the aux. tank because the fluid expands with heat and therefore won't fit into the closed cooling system anymore?

 

Here's a bad quality image of the radiator cap which I was able to cut out of my high resolution engine photo. If a closer photo helps, I will take it.

 

The radiator cap is pressurized because the coolant will boil at a higher temperature when the pressure is higher. Just like water will not boil at 212*F if under pressure. It will boil under 212*F if the pressure is less than sea level (that's why it takes longer to boil and egg in Denver then it does to boil an egg in Boston.).

If the pressure gets above 14# the rad cap will release the excess pressure into the coolant reservoir tank. Likewise, if the cooling system is overfilled and expands when hot it will purge the excess coolant into the coolant reservoir tank. Keep your coolant level in the reservoir at the specified level so the engine can take coolant when needed and put back in the tank when it has too much.

There is no need to have an original rad cap as long as the one you have is functioning o.k.

If you have the correct water pump matched to the engine and the radiator capacity, correct hoses, a working rad cap, a working thermostat installed correctly, 50/50 coolant and no restrictions you should have no problems with pressure if the engine is sound. If you think you might then just do a simple pressure test with a pressure guage rad cap.

Overheating issues involve more variables.

 

Thanks. Do you think the release handle on the cap acts exactly the same way as the overpressure valve on the cap? Should it release some of the coolant to the reservoir when I pull the handle? Cause it won't do it in my case...

I need to check the thermostat but do you have any tips on this?

At least there is no overheating involved with the cooling system, the temperature has always been perfectly normal and way below the red area.

 

Dont fiddle with the rad cap pressure release unless you need to take it off. Then just to be safe release any remaining pressure that might be in the system when the engine is cold. It relieves pressure and may not necessarily release coolant to the reservoir.

If the temp is o.k. and doesn't fluctuate a lot when the engine is warm I wouldn't mess with the thermostat. Since you just bought the car I would do these three things for sure.

1. Visually inspect the system for hoses, clamps, leaks and appearance of the coolant.
2. Test the coolant for protection to be suitable for your winters/summers. Don't check it at the overflow tank. Check it by taking a sample from the radiator.
3. Have the system pressure tested. Simple and cheap.

 

The hose is being blown off by excessive pressure in the cooling system. It is not hard to "break" the little Chevy motor. The heads often crack in the combustion chamber between the valves. The crack expands as the engine temp. and load increases. Just because you see no white smoke or cross contamination between the cooling system and oiling system does not mean all is well. You can purchase a simple diagnostic test kit to check for combustion gases in the cooling system at most auto parts stores, or you can put a radiator presssure tester on the radiator and do NOT pump it up, then run the motor and observe the gauge.

 

No thanks, I can see clearly enough.

Others have explained the theory of operation correctly.

I'm not convinced that this particular cap has the ability to release coolant to the overflow tank and then recover it when the motor cools.

 

So why does it not blow the coolant out the rad cap instead?

 

Run it with the cap off, you'll see the bubbles if the head gasket is leaking to the water jacket. You can also do a leakdown test to determine that, among other things.

 

Bingo ..


Test for cylinder pressure leaking into cooling system first.
There are a couple methods. Google for them.

The cap should have released and not the hose, unless you had so much pressure that it overcame even a good cap, and if that is the case, you have more serious problems.
The rad caps with the levers have always had a bad reputation of not working properly and consistantly. They were intended for the dumbass consumer that thought they just had to take it off while the system was hot. Just like the fuzzy spray paint to cover up a bald spot seen on the infomercials. People buy anything.
BTW You cannot judge a cap just by looking at it.

Get a real cap.


For a system with a recovery tank, there are 2 types available.
There are also caps available for a non recovery system, Be sure you have the right one.

With a drop center valve.




With a spring loaded valve



This disc valve at the bottom center of the cap controls the flow of coolant from the recovery tank.
The radiator should be full cold.
As the engine heats coolant expands and needs to go to the recovery tank.
As the coolant cools it is syphoned back into the radiator.
This keeps the radiator full of coolant for a number of reasons.

Buy the cap with the spring loaded valve rated at the proper 16psi and change it yearly. Around 5 bucks.

 

Thanks for all the help. I took the cap off my Jeep today and installed it on the Vette. The cap is rated at 18 LBS so perhaps slightly too high but should be still okay I guess. The cap looks somewhat different. The cap from my Corvette was by the way 16 LBS and it says 330 above it, probably some serial number for the product then.

I took some photos...






I added two exactly the same size green boxes to both caps. I used the left side handle-cap as reference (measured from the edge of the cap cover to the rubber sealing) and then placed the same size box to the Jeep cap, beginning from the cap cover. As you notice, the size of the handle-cap mechanism and also the blocking element is much larger. Maybe the end of the larger cap is just so big that even if pushed to the upper position by pressure, it won't move away from the small hole in the radiator that goes to the reservoir? Can you see a possible problem here?



Jeep cap fitted to the Corvette.


I ran the engine with the Jeep cap and it warmed up at high RPM for at least 5-7 minutes and then I let it run at normal idle for also at least 5 minutes. The hose went hard enough that I couldn't really push it completely together with my hand but I think it was a bit lower in pressure than it used to be. Unfortunately I cannot drive it anymore and perhaps it's impossible to get the engine warm enough at idle to test anything. Do you think it's supposed to release some of the coolant to the reservoir even when I just let it run on idle?

I don't know if it has any effect but just to test for the possible cylinder head pressure leak, I pushed the radiator hose together with my hand, held it and then gave remarkable throttle. I didn't notice any change in the hose pressure whatsoever.

 

Looks like your Jeep cooling system isn't in great shape either.

For it to blow into the resevoir tank start with a completely full radiator and warm it up with a towel or cardboard in front of the radiator fins. Watch the guage.

 

Haha, you are referring to the weird condition of the coolant on the cap? I was also surprised, I guess it could use a flush. Never had any visible issues with the Jeep cooling though.

Meanwhile I tested the cylinder head leak according to SH-60B's instructions. I ran it with the cap off, I placed a towel under the radiator hole to avoid the engine bay getting too "dirty" The coolant level was at the edge of the radiator, once then engine started up the coolant began to slowly drip out from the radiator onto my towel. There were no bubbles or anything whatsoever, the coolant was steady and smooth all the time. I ran it for 5 minutes like that, nothing changed.

I took the smaller radiator -> reservoir hose off from the reservoir and blew air through it. The hose seemed clean all the way to the top of the radiator, some coolant which was in the hose flew back to the radiator.

noonie: I will try warming it up like this in a minute. I will do it with the Jeep cap.

 

Hello fellas!

Time for an update. I finally borrowed my mechanic's cooling system pressure testing tool (Stant produced) and I tested it on the Vette. I think I did it wrong but I connected it with completely cold engine and then began to warm it up. The big radiator hose went very hard quite quickly and the pressure on the gauge also began to increase gradually. It was at 0 for a few minutes and then went up. I was firstly scared when the gauge was approaching the DANGER zone but then I turned it off, released some pressure by loosening the cap (a remarkable amount of coolant came out) and then started up the engine again. Now the pressure stayed somewhere in the middle of the scale and from that moment I filmed the testing as well. The gauge vibrates a bit at idle but is very solid when I add some gas. The pressure lowers a bit when I add throttle. I think the idle vibration is simply caused by the vibration of the engine and whole car, I couldn't even keep the camera steady when holding my hand on the car

So, here's the video:
http://www.youtube.com/watch?v=7VYz5iT8o54

Please check it out and see if you find anything weird...

I also bought a brand new 16 LBS Prestone radiator cap without the handle. Going to try how that works sometime soon.

Thank you!

 

Hi!

I've been doing some driving lately and I've kept my eye on the cooling system. Unfortunately it seems like I haven't solved the high pressure problem. Yesterday I drove more than 2 hours, new Prestone radiator cap installed, the upper rad. hose was relatively soft and the reservoir level was increasing nicely when the engine got hot. I checked the hose and level 4-5 times during the drive, I also drove motorway etc. No problems whatsoever and I was almost sure I fixed the issue.

However, today I went to drive again and after having driven about an hour, I opened the hood to check the hose and it was quite hard (not swelling though). The hose had moved a bit and would have probably become loose again if I hadn't tightened it over.

The reservoir level hadn't raised at all today, or perhaps a tiny bit (nothing compared to yesterday). When I loosened the rad cap by hand and let some pressure + coolant out, the upper hose instantly became soft.

I came home and I pulled off the reservoir hose from the radiator when the engine was hot. I wanted to see if it shoots some antifreeze out (to check if there is some blockage). Just a bit drained out and the upper hose stayed hard.

Then I took the Jeep's rad. cap and after running the car at idle about 15 minutes, the hose stayed soft but I didn't notice any increase in reservoir level. Again I thought that maybe the issue was now solved but apparently it wasn't. The hose became quite hard again, coolant level was same as cold in the reservoir.

There was another issue I told about that after driving around and doing some accelerations, the engine often begins to make a knocking noise from right front (related video here). I'm beginning to think that the cooling issue and that noise may be related to each other. Perhaps there is a blockage somewhere in the cooling lines in the engine block, one cylinder gets too hot, something swells up a bit with too much heat and things begin to make more noise? Perhaps the coolant doesn't flow properly because it can't make it through a channel in the block?

Still seems weird though... As far as I understand, if there is excessive pressure in the upper rad. hose, there is the same pressure in the whole radiator so the first place for the pressure to go would be the reservoir.

P.S.

When the knocking noise appeared and I then waited a bit + let out pressure and switched to the Jeep rad. cap, the knocking sound slowly began to disappear and then went away.

I am just completely mad at this situation. I'm not mad because the engine has a problem but I'm angry because I cannot figure out where it is. I hope you guys can give me some hints and what to check. Please help me get to the root of this problem. Thanks!!!!!!!!

 

Are you sure the cap is being installed FULLY each time it is removed? Turned fully clockwise till it hits the stops.
A cap that is not fully seated will not allow the coolant to reach the reservoir when hot. Thusly the pressure will build in the system and give a high pressure condition. I don't think the knocking is related to this problem IMO.
Sly

 

Keep at it Speedbird you will get it fixed. Sly Vette has a good point. You have to push down hard on the rad cap as you turn it to get it to the second detent and fully "on" position. Most caps have a stripe or an arrow that that, when aligned shows that the cap is fully "on". Remember you have to push down hard after the first detent to get the cap to the full "on" position.

Try doing a search on the CF or the Corvette Action Center knowledge base to see if anyone has had a similar issue. The "knocking" you hear might be purculating of the coolant. Here is a quote from one person trying to solve his cooling system issue.

cooling system:
after the car sat all night and it was nice and cold, the coolant lever should have been at the "COLD" mark on the expansion tank but it was WAY below that level so we filled up more coolant to bring it to the cold mark which took yet another almost 3/4 of a gallons. We let the motor run quite a while and she never went over approc 190* on the gauge and after shutting her down there was no more percoluating of the coolant like yesterday.
My buddy Tripp who was helping me out said the percoluting yesterday was just from air trapped in the system trying to get out and it was also keeping the coolant in the exp. tank from getting into the system and therefore it was percolating because of the air coming up thru the tank.

I noticed a lot of knocking yesterday during the drive down the road and back so knew we had to redo the timing and when we checked it it was way off so we brought it back to a good setting and I'm sure that is helping the car run at the lower operating temp we observed today - between the extra 3/4 of a gallon of coolant and the adjusted timing it's now running 15* or so cooler than it was yesterday.

P.S. Keep that pressure test cap handy.