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2002 nissan 2.5 se overheat
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dannypo
New User
Jun 10, 2008, 12:26 PM
Post #1 of 7
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2002 nissan 2.5 se overheat
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i have a 2002 nissan altima 2.5 se that has overheating problems. when i am on the road for an hour or so and doing above 60 mph with the a.c. on, the engine temp climbs and the a.c. starts blowing warm air. if i slow down to below 60 mph the engine cools down and the a.c. will blow cold air again. both cooling fans are operating and i have had the ssystem flushed and a new thermostat and control switch replaced to no avail. any ideas. this only occurs in the summer, of course.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 10, 2008, 3:54 PM
Post #2 of 7
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Re: 2002 nissan 2.5 se overheat
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Wow - a challenge! Ok - this is interesting as the A/C quits as the engine creaps up in temp at only highway speeds. One would think the airflow would be more than adequate even without fans.
Funny thing about air and the force it has. Forces of air at speed are "exponential" meaning the force triples with each doubling of velocity and aerodynamics come into play at speeds over say 50ish.
With that there's an airflow problem which could be a missing air dam under front bumper. The design is such that air makes a vacuum behind those which directs air of motion thru grille. If there's pressure under the bumper it could try to push back out the grille in a little battle of who wins. Don't know what this car uses exactly but those things get broken off on those cement parking things all the time and they are there for a reason. If that's missing or any shrouding around the fans it needs to be as originally intended. If you have a bug "bra" or one of those - try removing it.
Check that fans are pulling air thru the grille towards the engine just at idle. If that's backwards somehow it probably would still cool backwards until air speed and fans had a little dispute over who was boss and the effect might be like cardboard was covering your condenser and radiator?? Dunno - this is a good one!
The A/C part makes this interesting because designs have it that A/C gets first crack at cooling the condenser and the hell with the engine - most engines would still cool YOU while the thing was boiling over but if just so there could be "radiant" heat not allowing the condenser to cool and thus no A/C.
Check above things and note basic cleanliness of rad and cond for bugs, any dirt, plastic bag get up there - whatever.
If nothing wrong is noted, does just shutting off the A/C make engine temp come down?
T
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hermesco
New User
Aug 9, 2008, 7:49 PM
Post #3 of 7
(9315 views)
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Re: 2002 nissan 2.5 se overheat
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Any luck figuring out this problem? I'm having a very similar problem with my '02 Nissan Altima 2.5 SE with 84k mi. Some additional details I can provide are that the temperature gauge rises quickly (1-2 miles after starting) to and then hovers around the mid-point. When I start climbing a hill, the gauge rises up to the 90% level, depending upon the steepness of the grade. The AC cuts out at about the 75% level. Going down the other side of the hill, the gauge returns to the mid-point just about as quickly as it rose and the AC cuts back in at about the 70% level. The cooling/AC fans run most of the time, so I know they're working hard trying to cool things down. The engine temperature doesn't return as quickly on hotter days (> 85 deg.) and the overheating happens with and without the AC on (just more quickly with the additional AC load).
When this first started happening, I checked the coolant level. It was low, so I added about a quart or more of anti-freeze/water mix. Same problem heating quickly and overheating the following day. The coolant level is down another quart after ~500 mi. I've not seen any obvious signs of coolant leaks either on the garage floor, in the exhaust or in the oil. Oil level hasn't changed, so I'm thinking/hoping it's not a problem with the head gasket. So I'm not sure if the coolant loss is the cause or a symptom of the overheating problem.
Since the "Service Engine Soon" light is also on (constantly, not intermittently), and since I've been getting 10-20% better gas mileage (34-35 mpg highway instead of 29-30), I assumed that the problem was a bad O2 sensor causing the engine to run lean and hotter. However, when I took the car to AutoZone to check the codes, it only came up with P0217 - "Engine Overheat Condition". There were no O2 Sensor related codes listed, so I don't which sensor is bad. Replacing one sensor wouldn't be bad, but I'm not sure I want to replace both on a just a hunch.
The radiator seems OK - some bent fins, but not too many, and the fans are moving air to the engine. I don't see a black air dam, but don't recall if there ever was one or not. The problem also occurs in heavy in-town driving on hot days as well, when the car isn't moving that fast when an air dam wouldn't make much difference.
I'm stumped, so am open to any additional ideas.
Don
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Aug 10, 2008, 7:18 AM
Post #4 of 7
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Re: 2002 nissan 2.5 se overheat
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You say the fans run "most" of the time. If it's showing hot they should be on all the time and if not sensors may not be providing accurate info to them. Shutting down when hot is no doubt a fail safe mode.
Verify radiator is free and clear to exchange heat - flush as needed note what comes out as the whole system may be a bit dirty??
T
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hermesco
New User
Aug 24, 2008, 7:50 PM
Post #5 of 7
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Re: 2002 nissan 2.5 se overheat
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The fans run when the engine heats up to about 40% and above on the coolant temperature gauge - below that the fans do not run.
Last weekend I drained and removed the radiator and the coolant was clean. My coolant tester showed freeze protection to -20 & boil-over protection to 262 deg F. I then removed the radiator and cleaned the fins with water from the household hose/nozzle. It was quite dirty! I then sprayed the air conditioner cooling fins the same way (but in place). Next I used the hose/nozzle to back flush the radiator. It appeared that the water flowed more freely (more volume) through the radiator towards the end of the flush than at the beginning, but I'm not really sure. I then reassembled the radiator and added coolant/water mix.
As before, the coolant temperature never got above 50% while driving in the city (but the fans ran anytime the temperature gauge was above 40%). I took the car to the mountains again this weekend, and the temperature gauge rose to a max of ~65% at the crest of a long hill, but quickly returned to ~45% halfway down the other side. It previously got to ~90% on the same hill the weekend before the radiator cleaning (about the same ambient temperature both weekends), so I believe the cleaning helped.
I'm not sure if the radiator cleaning completely resolved the problem, since I don't recall how high the temperature gauge would rise before the Service Engine Soon light came on (which, by the way, turned off on it's own prior to the radiator cleaning). Although the coolant temperature gauge rarely gets above 50% now, it seems that the fans are still running more than before the problem was first encountered.
I still think that the engine is running hotter the usual. I'm also getting better than usual gas mileage  , which makes me think that it's running lean (which would also explain the engine running hotter). However, I haven't detected any pinging/knocking and the code reader doesn't show anything related to a lean condition. I still don't feel like replacing parts just to test this theory, so will continue to closely monitor the engine temperature. I may take the car in for an emissions test to verify/refute the lean theory - they're not mandated any more, so it will be interesting to see if the testing cost has gone up?
Don
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Aug 25, 2008, 3:12 AM
Post #6 of 7
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Re: 2002 nissan 2.5 se overheat
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Hi,
Wish we had split this thread back when as it starts with another's car.
Just some ideas and comments:
*I doubt if it's running well the engine is running lean and getting better MPG because of that. What will really make some measurable MPG difference is how much ethanol is in the fuel you buy perhaps. I notice it when I buy fuel in another state - specifically New Hampshire!
*Cleaning the flushing just the radiator seemed to make a substatial improvement! What kind of dirt are you getting? Bugs, plain road dirt, leaves of some sort? This may need to be a routine for you. Check that A/C (condenser) as it gets hit first AND they carry oil and leaks will clog those with dust dirt much faster if oily from a leak - common here with sand on roads used in Winter for traction to get leaks in those. Never mind that for fixing the leak if one is found but clean that with a degreaser like Westley's White Wall tire cleaner - carefully.
*Also check that the radiator cap or pressure cap is holding pressure. It can be tested or simply squeeze a radiator hose cool as reference and when warmed up (careful please) when fully warmed up. It should decidedly hold pressure or boiling point will drop dramatically especially in high atlitude use! (see next note)
*Anti-freeze testers and coolant: Many are off and always best to really know the % concentration by quarts used from known system capacity or try a couple different testers - shocking how bad they can be. Side note: Freeze protection is also related to poor cooling??!! The stronger the mixture (will read lower freeze #) the less efficient the coolant mix is and will boil more easily because of poor heat transfer. Never mind the boilover protection on guages as that is always referencing use of a 15# pressure cap. Ethylene Glycol itself is a poor coolant for cooling and doesn't raise boiling point much at all by itself but we need it not to freeze and it comes with anti-corrosives which are needed so it's a game. You said -20F was noted which should be fine for most. The recommended for most vehicles is 50/50 which yields -34F but doesn't cool as well as a weaker (more water) mixture but be careful of this and weaker is ok but changes should be increased corrosion protection. Some vehicles will specify much less concentration on purpose as heat exchange space/ability is limited so you would only find that for rare high performance cars and especially closed systems in auto-engined marine use!
Altitude notation: Water boils at 212F as we know at sea level. At altitudes it will boil significantly lower temps (mixed or not with anti-freeze) without pressure and there's a % loss of air density to cool the radiator so it's a double whack at a cooling system. All that and the load of going uphill as mentioned are pushing limits of automotive cooling systems. For most cars temp should stay stable once at operating temps. Load, altitude, and climbing a grade I'll allow some noticed higher operating temps but still within "safe" area on temp gauge. Higher speed increases airflow but higher speeds up grade at altitude ever increasing with thinner air is a factor as the speed is a load itself increasing engine heat. Depending on conditions of the day and situation it will be advised not to use "overdrive" in autos or the highest gear in standards (depending on each car)
************8
T
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Aug 25, 2008, 3:23 AM
Post #7 of 7
(9243 views)
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Re: 2002 nissan 2.5 se overheat
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You've noted such a change with just cleaning and flushing of just raditator that all needs consideration. Higher concentrations of anti-freeze also work against you for heat transfer. Boiling points listed include a working 15lbs pressure cap (check that) which is misleading as stronger anti-freeze mixes are more likely to over heat! EG anti-freeze by itself is a terrible heat exchanger.
Many factors of load, density of air for heat exchange come into play climbing hills in high altitude such that overdrive use would also hamper RPMs for water pump's flow rate and so on.
A/C's condenser (cooling fins in front of radiator) might show oil and collected dirt which would take a cleaner to remove and indicates a leak in A/C not relevant on it's own (the leak) for overheating but would hamper total air flow for engine's radiator. A/C use certainly adds to the heat load too,
T
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