Hi everyone. I have a 72 olds 350 cutlass. My engine is sill out of the car but I'm wondering if I made the right choice with the 195 degree thermostat and 16 lb radiator cap I purchased a new. I thought these were the OEM specs which is why I bought them. But the stat that was in the engine was a 180 and the cap was 13lbs. Any thoughts?
Thanks!
Chris

 

I would run a 180 thermostat with either cap.

 

Unless you are driving below freezing, 180 is fine. There are also more chances for leaks with higher cap pressures.

 

All your doing by running the 16#cap is extending the cooling systems boiling point capacity to 250+ degrees F. The system if in good shape will handle the difference.

 

The factory cap was 16 PSI. Use that one. The 180 t-stat is also fine.

 

Thanks guys!' Much appreciated.
Chris

 

1. Your engine has nominal 8.5:1 compression (probably actually a bit under 8), so you will not improve detonation with a cooler thermostat (you won't have any detonation no matter what).
There is no other reason that I know of to run the cooler thermostat if you cooling system is functioning as designed. Sometimes people whose cooling systems aren't working well will use a cooler thermostat to buy them some time before the car overheats, but that's all it will do if your cooling system is inadequate.

A 180° thermostat will not hurt anything as compared to a 195°, but your engine will run slightly less efficiently, and MAY get slightly worse fuel economy.
I have a 180° thermostat in my car, but that is because my engine has 10:1 compression, and I want to minimize the chance of detonation of pump fuel.


2. You should always use the radiator cap designed for the engine.
A lower pressure cap will not only reduce your potential boiling point, but it will reduce heat transfer at the interface between the head and the water flow, by allowing more areas of micro-boiling, where coolant is turned into a gas in a microscopic layer, which acts as a heat insulator. The higher the coolant pressure, the smaller this layer will be.


- Eric

 

Eric thanks so much for the info. So let me ask this. When the engine is running and the thermostat is open, where should the coolant level be in the radiator if I have the cap off and I'm looking inside? Where should it be with the cap off and the engine off ? I'm a long way off from this point but id like to be prepared. Thanks!
Chris

 

If the t-stat is open and the cap is off, the coolant level will be on the ground, because you will be boiling over at that point. The pressure cap is necessary to maintain the coolant below boiling point.

 

If you do not have an overflow tank, then you need to have a "pressure-only" cap (not "pressure-vacuum"), and you check the level with the engine cold and switched off.

The coolant should be at the level indicated by the embossed "——FILL LINE——" marking on the side of the tank, about 3" down from the filler.

- Eric

 

Thanks Eric and Joe. Joe- I remember when I first got the car back in 1993, the owner, Tony, would help me with the basics... I remember after we replaced the thermostat, he wanted to check for food flow so he would start the car, remove the cap, and we would watch the inside of the radiator and make sure that coolant was flowing through the small rectangular passages. When the coolant started to flow, I thought I remember the level dropping. Am I rembering this correctly?

 

Eric, how do I know if the cap is pressure only? I just bought an AC delco from rock auto, 16lbs with a safety lever. Is this correct? Thanks

 

One type of cap will say "Pressure" and the other will say "Pressure Vacuum."

Also the vacuum one has an extra rubber seal and valve in the center of the bottom of the cap.

- Eric

 

Yes, that is correct. If, however, you do have a true recovery system, the cap will allow coolant to be sucked back into the radiator from the tank as it cools. This eventually completely fills the radiator. If you open the cap on a newer car (when cool), you should see that the coolant is right up to the top of the filler neck.

 

Eric and Joe, so after reading both of your posts, is the pressure only cap used for a non recovery system whereas the pressure vacuum is for a recovery system?

 

Yup.

 

Ok. So I think I got the wrong cap. Mine is AC delco with 2 rubber seals 12r7s. Is there a number you reccomend? THanks!

 

The pressure-only cap has a one-way valve that only allows coolant to exit the overflow line when the system overheats. The pressure/vacuum cap has a second valve that allows the system to draw coolant back in from the recovery thank once the radiator cools down.



From http://www.allpar.com/fix/engines/cooling-caps.html

Note that most radiator cap listings show "open" or "closed" cooling system. The pressure/vacuum cap is for the closed type, with the recovery tank, however the reality is that pretty much all caps today are closed type, since these will work just fine on an open (non recovery tank) system.

 

Also assuming this is the cap for a recovery system what would be the repercussions by using it on a non recovery system? Would it suck air into the system?

 

Ok joe. I posted my last question before I read your post. So I should be fine with the recovery type cap on my open system correct?
Thanks!

 

It should work fine.

Interestingly, I just searched, and all of the common sources I could find listed only "Closed or Open" system caps, so it may be that, since these caps will work in the earlier systems, they've stopped making the Pressure-only caps.

- Eric

 

Thanks Eric! Thanks Joe!

 

Even the open style caps must allow air to be sucked back into the radiator. If they didn't the heated steam would escape when hot then the radiator would collapse under vacuum once it cooled. The primary difference is that the "open" system caps do not have the upper rubber seal to the top of the filler neck, "closed" system caps do. In addition, open system caps simply have a weighted disc that is normally open until pressure builds. This is the vent "seal". The closed caps have a similar vent but it is spring loaded closed so that a couple of psi of vacuum must be built up before is will suck the coolant back into the radiator. This level is low enough that it won't damage an "open" system radiator.

 

You guys are awesome!
Thank you!
Chris

 

Yes, but you must remember to not fill the radiator all the way. If you do, the cap will puke out the excess coolant, as it's designed to do. Which is fine, as long as you don't then refill the radiator to the top again and post here that your engine is "overheating" because it keeps "boiling over." With an open system, keep the fill level about 3" from the top, like Eric said. If it does puke anything out, just leave it be; it's telling you there's too much coolant.

 

Thanks Blackgold. Another question regarding the thermostat. The one I bought has a tiny circular opening with a piece of metal hanging in it, seemingly for coolant to always trickle through even when the stat is closed. Any insight to this?
Thanks,
Chris

 

I'm not completely sure what you mean. A picture would help.

- Eric

 

That thermo as an air bleed valve which allows air to bleed from the block as you fill. Some people actually drill an eighth inch hole in the thermo before installing.

 

Thanks guys. Ok so am I missing something? I tested the 195 degree stat by boiling water in a pot, and pouring it into a coffee can with the stat in it. It didn't open. I dropped my old
180 in and it opened. Went and got another 195 to replace it. Repeated the test and this one didn't open either. As I paraphrase what "Vincent Gallow"' in the movie My Cousin Vinny said " do the laws of physics not apply in my kitchen?"

 

Weird. I would expect a 195 to open. Mine always have.

Try just putting it in a pot and boiling it on the stove.

- Eric

 

Yeah, the boiling water (212 degrees) probably cooled down below 195 degrees after pouring it into the can.

 

A candy thermometer can be helpful in these cases.

- Eric

 

I agree with Kenneth. Why not just dip the thermo in the pot or set on something to get it off the bottom.

 

Yeah. I'll hang it from a wooden dowel stretched across the pot. Eric I do actually have a candy thermometer. I'll use that. Thanks!

 

I'm tagging on to a dormant thread-topic because I've got a Cooling System issue and this thread seems to be as close to my problems as I could find. I've read these posts with great interest but doesn't directly answer my concerns.
I've got a 70 Supreme with Rocket 350 and I can't seem to keep Coolant from Throwing-Up whenever I drive it for over 30 minutes. BUT It is NOT an "Over-Heating" issue. I have a New SW Temp gauge and my gauge never goes over 190 degrees. I'm running a new, good quality 160 degrees thermostat ..... with the 1/8" hole in the flange ..... a new water pump .... new hoses ..... new fan clutch ..... new radiator cap 16lbs ... correct mix of green coolant.
When I drive there is no indication of over-heating. BUT I'm constantly Barfing coolant. It seems as the only way it won't "throw-up" is if the radiator is only about 1/2 full. It seems to be "over-pressurized" ??
There is NO indication of smoke from the exhaust that would point to a bad head gasket.
Does anybody have advice as to what to try next ??
If there is not a bad head gasket ..... where else could "air" be getting into the cooling system ??
It seems to have started this problem after I replaced the original water pump with a New one. I did not buy a remanufactured water pump.
Thank you for reading, and hopefully steering me in the right direction!
Dave

 

Do you mean "1/2 full," or do you really mean "up to the Fill Line"?

- Eric

 

You are getting close to the procedure. The thermostat and water should be in an almost steady state condition where the thermostat's pellet heats up at the same rate as the water. The thermostat should not touch the container. You should monitor the process with a known good thermometer. Don't let the heat from the stove hit the top of the thermometer or you may get artificially high values. If you are near sea level the water should boil near 212F or 100C assuming it is relatively "pure" water. If the thermostat doesn't move near its rated temperature you probably have a defective thermostat. New doesn't necessarily mean good. Always verify performance.

 

I would need to officially measure tomorrow .... But I would say it's about 12" below the top row of cooling fins. Literally mid way down the height of the radiator.
Thanks. Dave

 

Okay, so not 3".

Have you checked to see whether the cooling system is pressurized by the engine before it warms up, as it would be from a head gasket leak?

Have you pressure tested the system?

Once the level gets to the point you mentioned, does it stop there, or does it keep going down?

- Eric

 

Are you running an over flow? It could be a weak rad cap.