Originally Posted by jr_ss

Correct, however, you should not have air bubbles in the coolant system what so ever. If its idling, and he is seeing air bubbles coming out, there is an issue some where and it's pressurizing the system.

Originally Posted by Mikester

Sorry- I realized that I hadn't completed my thought after "because" up there lol...

Edited last post.

Originally Posted by Kingtal0n

Nothing like a hot debate about hot fluids.

Many radiator caps are set to open around 15psi. Why not open at 1psi instead? Or 25psi? The whole point of having pressure in the coolant system is mainly to increase the boiling point of the fluids- thereby keeping it in a liquid form and not gaseous, which would potentially create hot spots. Imagine if a bubble of gaseous vapor forms around the combustion chamber? No more water can reach that spot and it turns into a "hot spot" capable of causing preignition.

So we need the pressure if the temperature is going over the atmospheric boiling point of water- about 212*F right?

Lets stop right there and draw a conclusion. If the water temp never hits 212*F, then technically, it never needs to be pressurized, because it will never change state (vaporize). But technically, we are wrong! Because most liquids, including water, have a partial pressure, meaning that water molecules are constantly escaping the surface of the liquid exposed to the pressure keeping it in a liquid state. That is why water evaporates from an open cup despite it being well below 212*F. SOME of the molecules near the surface of the liquid are moving fast enough to escape to gaseous state.

So, there is also a NEED to keep the water contained. That is, to prevent it's escape to the atmosphere. We can contain it in the coolant system if we seal the coolant system up, right? Well, we can try. Even a very tight coolant system is going to lose some water molecules over time.

But now we have an objective: keep the water molecules contained, and keep them in a liquid state by applying additional pressure when necessary to keep it from boiling.

Also, circulate it, such that it may exchange heat with the surrounding. Heat from the engine enters the coolant and raises the temperature. Heat gradually escapes to the atmosphere as the coolant is moving, not directly because it is moving, heat is transfering from not only the radiator but also the hoses and lines and even the engine block itself is losing heat of course. But we are expecting to get alot of heat in the coolant system and we are expecting the radiator to exchange enough of it with the surroundings to keep the engine's coolant temperature at a specific temperature.

WHAT temperature? While this is not part of my originally planned discussion, it makes sense to mention, heat is energy and more heat is more energy. Technically speaking, the more heat we keep around the engine, the better its efficiency will be, as long as the heat does not interfere with it's anticipated chemical reactions and processes. In other words, excessive temperature is bad because it does many horrible things to an engine, such as ruining the oil, causing detonation, excessively expanding metal parts and it can even deform them and cause engine failure.

But some heat is necessary. SO I ask again, what temperature? If you read around, you find that many recommendations will land you between 175-215*F. And choosing what temperature from that range is based on the engine you currently own. For a turbocharged engine (ours) we might anticipate a temperature rise during a full throttle run, perhaps 10-20*F rise in coolant temps on a drawn out 5th gear highway run. So it makes more sense to start low, around 180*F, and let it rise to around 200~

Lets start there. 180*F coolant temp. Yes, water is better than ethylene glycol at absorbing and storing heat without gaining temperature, that is, water's heat capacity (Joules of heat absorbed compared to increase in temperature) is very good, better than actual coolant. So run the most water you can for the best temperature stability. In Florida I run less than 20% coolant. Also, use DISTILLED WATER (or reverse osmosis). Never run tap water in anything you care about unless you need to limp home.

Last, these reasons already mentioned for the problem stated (blown HG, bad radiator cap) I agree with to start here, then branch out from there to more exotic possibilities.

Originally Posted by Mikester

Respectfully, the cap is not a factor- OP also has an open barb right under his radiator cap that should have a line connected to it going to the overflow reservoir... Between expansion/contraction of the coolant and revving the engine up & down, the system is going to "burp" out fluid and ingest air until he puts a hose on. Please watch the video and look where the fluid is coming out:



I am not sure if I posted the video correctly (at work, slow computer) so here is the link just in case: Sr20 coolant problem - YouTube

He needs an overflow hose... If you still don't believe me, then please go out to your car, pull the overflow hose off your radiator, start the car; give it some throttle and see what happens. I know from trolling that you are one of the smart guys on here; and I am thoroughly convinced that you will laugh (or at least see what I am saying) when you see the video. I am not trying to argue.

Originally Posted by Mikester

Dude, I mean absolutely no disrespect to you when I say I laughed my ass off when I saw that vid. you NEED a hose to the overflow reservoir. The reason it shoots out when you give it throttle is the pressure in the system increases when the water pump rotation speed increases... Anything under pressure (whether it be from the pump or heat or both) is going to migrate thru the path of least resistance. In this case, it's out the hole that should be connected to an overflow reservoir.

And then there's what Darren said below:



^^This is the fix. You don't need to do a leak-down test or check the head gasket for this one... The reason there are bubbles is because you are allowing air directly into the system via the very hole water is shooting out of... Every time you rev up, water shoots out... on rev down, air gets sucked in to take the place of the water... After doing it so many times, there is going to be air bubbles all throughout the system. If there were an overflow reservoir like there is supposed to be, only coolant would be able to flow in/out of the hole... keeping the system bubble-free.

It doesn't matter what the pressure rating of your cap is when there is a wide-open hole right under it. The overflow reservoir allows coolant to flow into it when its hot; and back into the radiator when it cools and/or the pressure subsides.

Originally Posted by Darren

the coolant in the system expands and contracts with different temps... the coolant overflow is not just for overheating, it's for expansion and contraction.

Just put a hose on the thing and call it a day.....

Originally Posted by cotbu

I'm taking the challenge!

I'll edit this post when I get back to the lab, but please comment.

Originally Posted by Mikester

Fair enough. So fair in fact that I felt compelled to go downstairs and unpack my radiator to figure out exactly why... I'm sure it's no surprise to y'all that it took all of 2 sec of taking the cap off and really "looking" at it to see

No excuses... The issue is elsewhere like jr_ss already said. I still hope by some chance it's a shit Vatozone [or incorrect replacement] cap; or the Isis radiator being Chinese crap...

I will now be quiet and follow