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Discussion Starter #1 (Edited)
Hello guys.. was hoping to get some explanation/help before i take my car to a shop or eve if i need to take it...

Give you quick background -- I recently moved to LA, where it's 100+ degrees right now, and before that i lived in Seattle, where it was 70-80 on a good day.

My car had an engine swap due to blown gasket and failed cooling system. When the engine got swapped out, all the hoses, gaskets, water pump and the like got swapped out. Not the radiator tho.

After that, for awhile my car was spewing coolant out of the coolant cap, so I was adding coolant little by little to the overflow tank.. and then I replaced the coolant cap and that stopped.

Here comes the oddities --
While I lived in Seattle, any time i looked and whether the engine was hot or not, the coolant was always below the MIN line. I didn't worry about it too much because it was always there, never empty and I didn't want to overfill in case the coolant went back into the overfill tank.

Whenever I would open the coolant cap, the coolant would be to the top of the radiator and I read that it was OK.

Oil is not frothed or white, bubbles don't come up when you take off the cap on the radiator and rev up the engine, exhaust is not white. So i dont think my head gasket is blown again.

I always monitored my coolant temp and it usually was inbetween 82 and 91, so never worried. Driving to LA on I5 never made the temp gauge go over 94.

After I moved, I've been driving here and the temperature is usually still under 92 degrees, even driving up to griffith park.

However, I looked at my overflow tank today about 3 hours after the engine was turned off (so still pretty hot) and it was above the MAX line.

So now I'm worried - should it be above the MAX line, is it going to get sucked in back into the radiator, what is going on?:hmm:

Could someone please advise..
 

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what is going on?:hmm:

Could someone please advise..
When the radiator fluid heats up, it expands, causing pressure to build up in the system. The pressure is relieved via the radiator cap which allows the coolant to flow into the expansion tank. When the coolant cools back down, a vacuum is created in the cooling system that sucks the coolant back into the radiator from the expansion tank.

Assuming all is ok with your cooling system, the volume in the expansion tank will fluctuate. Nissan states in the owner's manual to check the coolant level in the expansion tank / reservoir when the engine is cold, and to service it to the MAX level if it is below the MIN level (again, when the engine is cold). Edit: to clarify, a hot engine will likely show above the MAX line, which is why they want you to check it cold.

If you constantly have to add fluid, then it is likely that you have a small leak somewhere. If your expansion tank appears completely empty, then it would be a good idea to check the level in the radiator first, and then service the expansion tank.

Hope that answers your question.
 

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Discussion Starter #3
Thanks for the reply.

To clarify - I checked the fluid this morning, when the engine was cold, and it was over the MAX line. In the past the coolant was always below the MIN line when engine cold, but I stopped adding fluid after I replaced the radiator cap.

I'm 99% sure I don't have anymore leaks in the system.

Based on what you said, my understanding is that for the longest time the pressure wasn't high enough in the radiator to cause the cap to open up and spill the fluid over into the expansion tank and only recently has it opened up and expanded the fluid.

That makes me think that something (?) caused the pressure to rise?
 

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The system pressure is controlled by the radiator cap. Make sure you have one that is correct for your system. If your system overheats, it can also cause it to consistently vent large amounts of fluid into the catch tank, but it should all go back in when it cools off, unless you vent so much of it that it spills out.

You may have had a bunch of air in your system (which is very common after system maintenance). If the cold level is above MAX, you probably have slowly eliminated all the air and it can't take anymore coolant.
 

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Discussion Starter #5
But it used to be that the coolant was at MIN in the past .. with engine cold.

Wouldn't it be that if all air left and it sucked the rest of the coolant in, my overflow tank would be completely empty?

If I understand the system correctly, the pressure cap is there to relieve pressure... and the only way pressure builds up is due to heating... so if the PSI gets too high (my cap is at 13 i think), it would spill over -- but then suck it back in.

It is almost as if there is air in my system... or exhaust gases?

If I do open up the radcap on a cold engine, would should I expect - should I see coolant to the top of the radiator or not?
 

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But it used to be that the coolant was at MIN in the past .. with engine cold.
That's normal operation. As long as the cold coolant is between min and max you have no problems. Even in a tight system, you will eventually have to add some to replace what is lost due to evaporation.

Wouldn't it be that if all air left and it sucked the rest of the coolant in, my overflow tank would be completely empty?
No. Not necessarily. The min max overflow design keeps more than is needed in the catch tank to compensate for slight quantity variances in the radiator / system. It's essentially a closed system. It only holds so much coolant. If you are constantly having to add fluid you either have a leak or you have air that is slowly being expelled and replaced with the fluid you are adding. But since air is compressible, it is possible to have trapped air in a system for a very long time.

If I understand the system correctly, the pressure cap is there to relieve pressure... and the only way pressure builds up is due to heating... so if the PSI gets too high (my cap is at 13 i think), it would spill over -- but then suck it back in.
It will spill over regardless. That's normal, and that's what the catch tank is for. The radiator cap is there to increase the boiling temperature of the water (like a pressure cooker) because recip engines work best when operating around or above the boiling temp. The different caps are set to accommodate different system designs.

It is almost as if there is air in my system... or exhaust gases?
If you have air or bubbles in your system, then you still have a leak or lots of trapped air, even if it's not leaking on your driveway. Gasses leaking in your system from your engine can cause an overflowing reservoir tank according to the FSM.


If I do open up the radcap on a cold engine, would should I expect - should I see coolant to the top of the radiator or not?
Nissan uses a special venturi tool to fill the radiator under pressure. Most people won't have one. You are supposed to fill the radiator, install the radiator cap, service the reservoir tank, run the engine with the heater on full hot, then adjust the reservoir level as required to maintain the min max level when cold. The radiator itself will seek and maintain its own level, and once all the air is out of the system the level will stabilize. The only level you need to be concerned about is the catch tank min max.
 

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Discussion Starter #7
Hmm ok. Thanks for the info - quite detailed :)
honestly, i'm still confused tho - anyone else might be able to chime in?

Also, this morning, after letting the car sit overnight to cool down, I opened the radiator cap - saw the coolant in the radiator up to the top. Turned on the engine to check for bubbles, but within a couple of seconds i saw the coolant moving and starting to rise. In the past, i've been able to keep the cap open for 30-40 seconds and never had the coolant rise. I'm not sure if that is normal...

The starting temperature of the truck was around 40 degrees C, as measured from the ODB. In the past it usually was in the 20s. Went from 40 to 80 (operating temperature) in about 3-4 minutes of city driving.
 

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honestly, i'm still confused tho - anyone else might be able to chime in?
It might help if you provided us with more information.

What is the year model of your truck?
If it's a first gen: What engine do you have?
Does your engine actually overheat?
Is it blowing out white smoke?
Is your reservoir overflowing?

I haven't checked every manual, but the servicing procedures, parts, are likely to be slightly different (cap relief pressures are different) and on my second gen, the radiator cap and reservoir caps are different and not interchangeable. The 2000 V-6 has an air relief plug that has to be removed while servicing. etc etc.
 

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Discussion Starter #9
It's a first-gen, 2000.
VG33E
The engine doesn't overheat - the temp stays between 80-90 degrees C.
No white smoke.
The reservoir hasn't overflown yet, at least I dont see it.

But like I noted before - it went from almost MIN (a little below even) to over MAX. And it was at MIN for the 4 month since the engine swap/coolant system service. So something - i'm not sure what, and that's why i'm here - caused it to fill up the overflow tank. It has stayed at the same position (over max) for the last week - not less, not more.
 

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It's a first-gen, 2000.
VG33E
The engine doesn't overheat - the temp stays between 80-90 degrees C.
The thermostat doesn't even open until 82C / 180F, so if those numbers are correct, then you aren't overheating. Operating temps will vary with conditions, but it should be in the neighborhood of 200F / 90C.

Servicing procedure is here:
http://www.nicoclub.com/FSM/Xterra/2000/ma.pdf

scroll to page MA-28

Edit: File this in the "for what it's worth" category, but my second gen has been slightly over the max line since I bought it, and I can't see fluid in the top of the radiator when it is cool. It runs just fine and has never had any maintenance at 50k miles.
 

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Discussion Starter #11
On MA28, step 4

4. Warm up engine to normal operating temperature without
radiator cap installed

So it is assumed the coolant won't rise with the cap open (and in the past, it never has - i used to be able to keep the cap off). Now if I start the engine with the cap off, the coolant will start rising and will spill out of the radiator head.
 

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In your first post, you said "the engine got swapped out, all the hoses, gaskets, water pump and the like got swapped out."

Swapped out with new parts? Thermostat too? Was the relief plug removed when serviced?
 

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Discussion Starter #13
Yes, new parts, new thermostat. Not sure about the relief plug - but I trust my mechanic he did a good job.
 

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Ok then, let's move on to your statement:

"so it is assumed the coolant won't rise with the cap open (and in the past, it never has - i used to be able to keep the cap off). Now if I start the engine with the cap off, the coolant will start rising and will spill out of the radiator head."

First off, hot coolant will rise in the radiator as it expands with the cap on or off. The radiator cap is supposed to keep it inside the radiator under pressure until the relief pressure is reached (and then it escapes into the reservoir).

What Nissan is assuming here is that you are starting off with an empty system (refilling engine coolant). Typically the radiator level will remain constant until the engine temp rises enough to open the thermostat. When that happens you will usually see a slight drop in the level as the air in the system is replaced with coolant, followed by a rise as the fluid heats up and expands. I would interpret Nissan's instructions to mean that they want the expanded hot fluid level to be at the level of the radiator neck while you are servicing it at first. In steps 6- 8, they tell you to fill the cold engine and repeat the process with the cap installed until the coolant level in the reservoir no longer drops. If you ran it with the cap off at that step, it is likely to overflow, which is why they want the cap back on.

If you start off with fluid bubbling out of the neck on a cold engine, that's typically an indication of a blown head gasket. However, you stated that you have no other indications of that, so let's say that's not the case.

You may just have too much coolant in the system. Your engine isn't overheating and there doesn't appear to be any driveability issues. If you are really concerned, then service the system per Nissan's instructions from beginning to end to make sure you don't have air in the system and to correct the level.
 

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Ok I seem to be having a similar problem with my 2006 exterra. When it is cold I take cap off and start it is immediately pushing coolant out no bubbles not hot at all never seen anything like that before on any other vehicles iv had. But if I have it filled and bleed when I'm driving it will blow out the coolant threw collection tank then cools takes back all from collection tank and I open radiator and it will still except 3/4 gallons of coolant. Any help please I'm puzzled.
 

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Do you have a belt driven fan or an electric unit? A belt driven fan may well have a bad clutch. Check rubber hose clamps from radiator expansion in/outlet and expansion tank in/outlet lose clamps may well allow very small leaks as you drive and you may well not notice the loss. Does it smell like coolant after you have driven it for a while and stopped?
 
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