sr20de...old radiator (i guess) popped like a balloon, new one hisses. Not (specifically) the thermostat. Wut do?

[plaguedoct0r]

Hey guys, thanks for reading.

STRAIGHT TO IT, from Aus (Jap model cars) manual Nissan NX-r 1994, sr20de 2.0 (NA)

Got a new, all aluminium radiator (rated for fit in my exact model) because the old one got a leak (probably popped like a balloon). The old one could never drive on highways because it would overheat, but would never overheat if it didn't get above 80km/h (50mph-ish???).
ANYWHO, replaced it, now I get a hissing noise emitted from the radiator cap after I drive for 10 minutes or more. (How many minutes in an american minute??? --)
It's a backlash of pressure from the pump, obviously. But I don't know where the issue is and I need a step-by-step of how to troubleshoot my problem.

- I have recently replaced the thermostat, which wasn't the problem at the time, though I did put stop leak in it after... And it's not likely the issue now because it still hisses when I have the heater on. Plus, previously I ran the car without a thermostat at all and it still overheated without loosing much coolant volume (barely a single handful on 1hour+ drives). Perhaps it's whatever actually physically contacts the motor and detects the heat, or whatever powers the thermostat itself, but it almost definitely isn't the thermostat.
- I replaced the radiator but didn't get my system flushed (properly, that is... I put a hose in one end and blasted it till it came out clear. The back-pressure didn't seem so severe to my limited knowledge of cars. It's not like it was just rushing through like a hose pipe, but it didn't seem to be like...CLOGGED clogged either).
- I didn't use the radiator cap that came with the radiator, though the cap I use is a perfect and snug fit (radiator is rated to fit my model car and the cap hole looked and felt the exact same). Otherwise I wouldn't have used it at all, of course...
- There doesn't appear to be any leakages (even around the cap itself) despite the hissing (system is definitely full of fluid though)
- Took it to a mechanic recently because of what turned out to be a fuel pump issue (I guessed it. Through all of this, at least I got that :P). They didn't say anything about a radiator issue (they may not have had reason to though. Driving less than 10 mins and what not). I have a sneaking, perhaps paranoid, theory that he put the wrong spark plugs in my car at this time. He definitely replaced them, and my car can take both 1.1mm and 0.8mm gap plugs, and it felt a lot less responsive when I got it back from him.

Stuff that I'm unsure of it's importance:
- The steering felt a bit resistant when I got it back from the mechanic.
- ABS was playing up shortly before all this, though it was likely the gunk that got cleaned from my brakes (still...electrical problem???)
- Battery replaced very recently too.

Thanks again for reading. Hope you can help. I'm poor but capable and logical!!!

[shorod]

For starter, have you checked to ensure the electric cooling fan runs? The electric fan should run as the engine gets up to temperature to maintain the system temperature. If the fan does not run, the car will overheat and that overheating creates excess pressure in the cooling system.

Typically cooling fans not running will NOT show as an issue at highway speeds. When vehicles overheat at highway speeds that's usually due something restricting airflow through the radiator such as a piece of cardboard or leaves/bugs that clog the fins of the radiator or A/C condenser.

I certainly would not say your hissing is due to excess pressure from the pump. It would be more likely due to too little flow from the pump causing the coolant to overheat. If the cooling system has not seen regular maintenance, there's a reasonably good chance that the water pump is starting to deteriorate. Maybe the fins have corroded to the point where they no longer circulate coolant with enough volume. And this lack of flow could also explain why you have overheating at highway speeds. I'm assuming if there was something restricting air flow through the radiator you would have noticed this when replacing the radiator.

Finally, the pressure cap needs to maintain the vehicle's rated pressure in order to provide correct boil-over protection. The pressure of the system helps raise the boiling point. You mention the cap is not the one that came with the radiator. Is it new, or could it be worn out and not functioning properly?

-Rod

[plaguedoct0r]

Fans definitely run. They're electric and do so periodically, so it's difficult for me to know if its correct timing or not. However, since it maintains a decent temperature within somewhat normal use over a period of 45 mins plus, I don't think it could possibly be the fans.

Also, you keep saying "airflow". It should be "waterflow" or "coolantflow" or some variant. Probably irrelevant... Sorry...

The issue cannot be from reduced flow from the pump, otherwise there would be no hissing. If the pump couldn't flow, then there wouldn't be any pressure inside the system to create the hissing noise in the first place.

Also, the fins likely cannot be clogged because the radiator is new. The symptoms presented immediately after installing the new radiator.

- The issue is DURING or BEFORE the thermostat, but almost definitely does not involve the radiator or thermostat itself.

I greatly doubt that the cap is the issue. As I said it fits VERY snugly. As though it was made for the radiator (though it's definitely the other way round).

This is more than likely some sort of blockage or electrical problem.

I welcome troubleshooting advice, I have no ego, but still I bear no baseless illogical criticisms. I included things like the radiator cap MORESO to ellude to its irrelevance. How often is a radiator cap related to a car consistently overheating?

Not that I won't test this conclusion, but it just seems too detached from the real problem, is all...

[plaguedoct0r]

Like I said, I will listen to almost anything. Please put in your 2 sense

[shorod]

Originally Posted by plaguedoct0r

Also, you keep saying "airflow". It should be "waterflow" or "coolantflow" or some variant. Probably irrelevant... Sorry...

Nope, I mean airflow. The radiator is a water to air heat exchanger. In order for it to cool the engine coolant, it needs air to move through it. That's what the electric fans do, they move air through the radiator. However, in order for the fans to do their job, the path for air through the radiator needs to be open and not obstructed by leaves, cardboard, etc.

Originally Posted by plaguedoct0r

The issue cannot be from reduced flow from the pump, otherwise there would be no hissing. If the pump couldn't flow, then there wouldn't be any pressure inside the system to create the hissing noise in the first place.

Yes, it can be from reduced flow. Think of a teapot heating up. As it heats, it whistles from the water boiling. There is no "pump" or mechanical movement of the water in the teapot, yet it still whistles. That's similar to what is happening in your cooling system when you hear the hissing. The hissing is the coolant boiling and the steam from the boiling exiting the system through the radiator cap and overflow tank.

Originally Posted by plaguedoct0r

Also, the fins likely cannot be clogged because the radiator is new. The symptoms presented immediately after installing the new radiator.

Ahh, now we're getting somewhere. If you didn't have this issue before installing the radiator, there's a good chance you have an air pocket in the cooling system. Before you respond that "it can't be an air pocket because you didn't install any air, only coolant" remember, if coolant was getting out, it was being replaced by air. So with the leak from the old radiator, air was getting in. When you drained the system to install the new radiator, air was getting in. And if the air pocket ends up at the top of the radiator, it will not suck in coolant from the overflow tank as the level drops. Also, if the air pocket is at the top of the engine block, the thermostat may not open to allow the water pump to pump the coolant through the radiator. The thermostat opens based on the temperature it's immersed in. If it's immersed in air, the air may not be as hot as the coolant or the thermal mass of the air may not be sufficient to open the thermostat.

Originally Posted by plaguedoct0r

- The issue is DURING or BEFORE the thermostat, but almost definitely does not involve the radiator or thermostat themselves.

Read above.

Originally Posted by plaguedoct0r

I greatly doubt that the cap is the issue. As I said it fits VERY snugly. As though it was made for the radiator (though it's definitely the other way round).
And besides, the differing cap would present a major problem that was not present before, rather than a continuous pressure problem.

The form factor of the radiator cap is somewhat irrelevant to whether or not it is working properly. The cap is not simply a cap, it is a "pressure" cap. Somewhere on the cap it will likely say something like "15 psi" or whatever pressure units are standard in your region. It needs to be able to maintain the system pressure to a level specific to the system. If the cap is worn out, it may not allow the system to build pressure which will lower the boiling point of the coolant. If it does not allow the system to bleed off excess pressure, it could allow the pressure to build high enough to cause leaks. What did you say the failure mode of the previous radiator was? Oh yeah, "popped like a balloon".

Originally Posted by plaguedoct0r

This is more than likely some sort of blockage or electrical problem.

I welcome troubleshooting advice, I have no ego, but still I bear no baseless illogical criticisms. I included things like the radiator cap MORESO to ellude to its irrelevance. How often is a radiator cap related to a car consistently overheating?

Not that I won't test this conclusion, but it just seems too detached from the real problem, is all...

You're welcome to ignore my comments and experience all you want. I think I've provided rationale above, and I think with some researching on your part you'll find that greater than 90% of what I've suggested above is sound and of good troubleshooting procedure. As far as I know 100% is accurate, but I realize I'm not always right. In order to determine what the problem is it can be just as helpful to rule things out. But please don't just rule the easy and free things out because they don't seem to make sense to you, ask questions, do research.

-Rod

[vgames33]

- Overheating on the highway with the old radiator, leaking (likely from the side tanks).

- Hissing sounds suggesting a build up of pressure in new (all aluminum) radiator.

- Overheating without losing coolant, even with the thermostat removed, only at high speed.

Sounds like the pump lost its fins or you may have a leaking head gasket (likely from repeated overheating). Does it still overheat?

The hissing could very well be from a bad cap not sealing well and venting pressure.

[shorod]

Plaguedoct0r, in response to your "ps" notes now on your first post, please see your Private Message. I pasted in two sentences from your original post which clearly shows why I made the original edits. There is no "point" system for moderators, but we do try to keep the forum family-friendly.

-Rod