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02 Altima overheats w/ full coolant

I have an Altima that has gone through a routine of nearly overheating several times over the past couple of summers. From what I’ve read online, it could be a problem with the thermostat, head gasket or water pump, but so far the mechanic has found nothing to explain it. Here’s the full story:

02 Altima, mileage in the mid-100s. Temp gauge rises quickly all of a sudden after staying around the middle for the first 20-30 minutes of driving. Temp rises during city driving, not highway (maybe thanks to air flow?). When temp rises, turning heat on brings the needle back down for a while (not fun in 80-90 degree heat). The problem persists typically until I get the oil changed, but the oil level is good, and then goes away only to return months later (this part perplexes me). Coolant also is full, but level seems to drop more quickly than it should (I refill every 2-4 months). No obvious evidence of leak. I’m not certain about the timing, but it seems that the overheating problem is usually presaged by the sound of liquid swishing around somewhere under the hood while driving. The sound is most noticeable when car first moves after being parked; sounds like there are gallons of water directly under the dashboard rushing from one side to the other. Coolant maybe? Coolant is visible in the radiator, but I’m not sure whether there’s sufficient flow through it. Running AC causes overheating more quickly. Lately, perhaps unrelated, at ignition there is some hesitation to start, like it’s not getting enough gas. For now, I’m assuming this is a separate issue with the carburetor, fuel filter, etc. but I’m including the info just in case.

The Radiator Should Be Full When The Car Is Cold.

You state, "Coolant is visible in the radiator . . . ", but Is it full?

You have some air trapped in the cooling system (causing the swishing sound in the heater core under the dashboard and probably erratic temperature swings).

You could try a new thermostat and having the air purged from the system, but you should have the cooling system pressure tested to see if it holds pressure over time. There could be a leak somewhere that introduces air into the closed cooling system.

I wouldn’t keep operating the vehicle without finding out where that coolant is going. You could go from a minor problem to a major problem by doing so.

Let’s worry about the starting problem, later.


The coolant level in the reservoir is full. Is there a way to check the level actually in the radiator?

Oooo, Maybe not. All My Cars Have Radiator Caps. Your’s May Not.

Has the cooling system been pressure tested? I’d still go that route.


First of all, if you have to replace coolant there is a leak somewhere, either external or internal. Under normal circumstances you should NOT have to add coolant every few months.

This loss of coolant accounts for the “swishing” sounds you hear. There is air in the cooling system, and the noise is the coolant rushing in to fill the empty space when you start the engine. The heater core is under the dashboard, which is where the noise is coming from.

Air in the cooling system will make the temperature gauge spike, exactly as you describe. You need to bleed the air out of the system and make sure it is full of coolant all the way through the system. The coolant level (checked when cold) in the radiator should be right up to the cap. No empty space at all.

Then you need to figure out where the coolant is going, and why you have to keep adding more.

The starting issue is separate. You didn’t tell us anything about the maintenance history of this “mid 100s” vehicle, so there are multiple possible causes for this problem. The carburetor, however, is not one of them. Your Altima is fuel injected. There is no carburetor.

When I open the radiator cap, I can see down only about an inch or two. Coolant sits in that portion of the radiator when cool, maybe a quarter of an inch deep.

Thanks for all the input. I think I have a starting point now. I’m not certain of the history. It’s not “my” car but my girlfriend’s. I meant fuel injection… just accustomed to talking about my Gremlin I guess and not these new-fangled machines.

You have a Gremlin AND a girlfriend?


On a related note, given that she had provided all of this info to her mechanic a couple of times before and his response was that the swishing sound is probably due to the drop in coolant level but that she should bring it in if it happens again because he couldn’t find the problem, and he didn’t bleed the air from the system or even mention it as a possible fix, is it time to find another mechanic?

Gremlins (especially those greenish ones) Are Chick Magnets!


The same mechanic looked at it this morning. His diagnosis:
The catalytic converter needs to be replaced and there is a clog, leading to the frequent overheating. $1200 to fix. Sound reasonable? (I’m hearing this second-hand, so I apologize for the limited info).

Further issues now - I’ve been reading online that there was a recall for this year/model regarding the catalytic converter. The symptoms victims of this problem have experienced are different (e.g. burning through lots of oil). But could this be the culprit, since the CC was never replaced per the recall? Reading through threads regarding this issue has me scared that the car will soon die a slow and painful death, but only after we waste thousands of dollars trying to fix it.

How a catalytic converter can contribute to oil burning is beyond me.

I would get a second opinion. A radiator shop should be able to diagnose a clog, if it exists. The rad can be removed and flow tested. A shop that has a hydrocarbon sniffer can also detect if combustion gasses are getting into the cooling system by holding the probe at the open radiator cap. I think there are chemical test strips that can detect HC in the coolant, too. If HC is detected, a blown head gasket is the most likely cause.

A good mechanic should help you do first things first. Don’t spend money on a converter until the engine is in good shape. After overheating and losing coolant, a head gasket job may be all that’s needed, but more serious problems like a cracked head or block, or worn bearings, may be lurking.