How many lbs radiator pressure cap is optimal?

[vector1]

i talked to howe because i had a car show up with a ruined radiator (howe brand) and they recommended a 22-24 lb. cap. the radiator actually had the cooling tubes expanded so no air could flow through. i asked them how this could happen and he explained that when an air bubble is ran through them it is real easy to do. i should have asked how but he didn't elaborate. the radiator had a 16 lb. cap installed and the puke hose was ran to the top of the catch can which is prob why the head gasket was leaking and blowing the coolant and filling the system with air, because the coolant was being expelled and not recovered. by the way my jbl was doing the same thing because the catch can was also hooked up incorrectly by the po, blowing coolant and not recovering which led to a leaking head gasket.

the cooling system i am currently running on the jbl is using a 22# cap. the puke tube is running to the bottom of a catch can with the catch can filled 1/2 full. the top of the catch can is prob inline with the top coolant hose. i am running a stewart high flow 180 thermostat with three drilled holes purchased from speedway already drilled. there is no air in the system, none, nada, zilch. when the system heats up the coolant is pushed into the catch can and when it cools down the coolant is drawn back into the main system. after the system cools i can take the cap off and it is filled 100% with coolant. this is on an all aluminum engine so i would think if the pressure was too much it would show on this setup.

i think unless you have air in the system because of hydraulics the cap is going to let go no matter what. my top tube is inline with the top of the engine, so its either going to contain quite a bit of air in the top hose, engine, and radiator, or 100% coolant, i went with the latter.

i had an oem 195 thermostat with two holes installed and the temp would fluctuate too much, i like the stewart high flow 180 much better for holding temp and should work well for racing.

hth

[1985 CCX]

I use water and wetter with about 10% antifreeze. 16lb cap

[RICK LAKE]

DocDirk Doc you shouldn't need anything more than a 15# cap. What thermostat are you running in the motor? Run a 180 temp would be about the best for your area. Do you have a shroud on the coolant fan? You want to pull as much air through the rad to control and lower the coolant temp. Water pump, who's do you have? Here's the best one, are you running UNDER DRIVE PULLEYS???from March?? They don't spin the water pump over fast enough to cool the motor and control heat. If the car sat for a couple of months you might want to replace the thermostat first. Drill a couple of 1/8" holes in the edge of the thermostat to help remove air from the coolant system. Make sure that is not alot of debrie in the fins on the radiator. One more check is to make sure that the rad has no cool spots. This could mean that the tubes are not flowing. Anything more than 16# cap you are looking at possible loosing on a hose to this much pressure. How low has the motor been built and running. Do you hear and bubbling or gruging sound coming from the motor when hot? Before you start playing with anything, get a infrared temp gun and check to see what the coolant temps are around the motor and rad. It is VERY POSSIBLE that your coolant gauage could be 10-20 degrees off and there is no problem. Let's do the basics first before we go hunting for a nightmare. This has happened before to other guys here. Rick L. Ps you have PM.

[DocDirk]

Originally Posted by RICK LAKE

DocDirk Doc you shouldn't need anything more than a 15# cap. What thermostat are you running in the motor? Run a 180 temp would be about the best for your area. Do you have a shroud on the coolant fan? You want to pull as much air through the rad to control and lower the coolant temp. Water pump, who's do you have? Here's the best one, are you running UNDER DRIVE PULLEYS???from March?? They don't spin the water pump over fast enough to cool the motor and control heat. If the car sat for a couple of months you might want to replace the thermostat first. Drill a couple of 1/8" holes in the edge of the thermostat to help remove air from the coolant system. Make sure that is not alot of debrie in the fins on the radiator. One more check is to make sure that the rad has no cool spots. This could mean that the tubes are not flowing. Anything more than 16# cap you are looking at possible loosing on a hose to this much pressure. How low has the motor been built and running. Do you hear and bubbling or gruging sound coming from the motor when hot? Before you start playing with anything, get a infrared temp gun and check to see what the coolant temps are around the motor and rad. It is VERY POSSIBLE that your coolant gauage could be 10-20 degrees off and there is no problem. Let's do the basics first before we go hunting for a nightmare. This has happened before to other guys here. Rick L. Ps you have PM.

Rick,

My current radiator cap is 16#. I'm running a 180 top quality thermostat but have not drilled holes in it yet. I saw one from Speedway that has them already. My engine is relatively new, less than 15 hours on it. There is no debris on the radiator. I'll check for radiator cool spots. I shall get the infrared temp gun as I want to check across my tires for best inflation pressure too. No bubbling or other strange sounds from the motor when it's hot that I can tell (lumpy cam and loud exhaust excluded). I have relocated my temp gauge to the block because of a complicated setup with the surge tank line to the thermostat housing and I'm told by some that's fine and by others it's reading too low there. My radiator is shrouded to the fan but not in front from the opening of the car. The water pump is rated 20% over stock output and it's OVERdriven by a pulley smaller than the crank pulley. Up until the hot weather spell the car was running at a steady 185 with a 180 thermostat so I figured the temp gauge was probably accurate. Some have suggested I'm pushing too much water through the system. I'm soon going to reroute the fill hose exiting the surge tank away from the intake side of the radiator to the low pressure side of the water pump as it may currently be providing a way for the radiator to be partially bypassed through the surge tank:. I"m sure I'll have this all sorted out and enjoying trouble-free worry-free driving by 2012 Thanks for your thoughtful analysis!

Regards,

Dirk