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How to stop (hopefully false) random overheating condition?

2K views 5 replies 5 participants last post by  bcohen 
#1 ·
This is in regard to a 1995 Caravan with a 2.5L 4-cylinder engine.

I have done a lot of work on this van recently (discussed in another thread) and now it is running great, and no leaks anywhere that I can see. However, one problem has apparently continued, which is that approximately once every 15 to 20 times that I drive the van, I see what I assume is a false overheating condition.

What will happen is that the engine temperature gauge will start creeping up over a period of 1 to 3 minutes, get to the tick mark just under the maximum, then the "check gauges" light comes on, and an alarm sounds. It will stay there for a minute or two, then it just drops back to the normal position, which is just below the middle tick mark.

Since I don't believe that the engine could really overheat that fast, and certainly if it was overheated, it wouldn't cool off to normal so quickly, I assume this is a wiring or computer issue? I have already replaced both coolant temperature sensors, and I used the MotoRad thermostat which has a small orifice to allow a small amount of coolant flow at all times, even when the thermostat is closed. There is no evidence of air or other gases in the coolant lines or radiator. There is no loss or contamination of the oil or coolant, either.

Any ideas? Is this something that a shop with the factory scan tool could pinpoint, based on information stored in the PCM? This is a very intermittent problem, i.e. I could take a 50+ mile round trip with mixed freeway driving and city driving and not see it, and then it could happen on a short 2-mile trip to buy groceries. It has happened while driving at speed on a freeway, it has happened while driving in stop-and-go traffic, and it has even happened while idling at a busy intersection.
 
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#2 ·
Radiator cap new or old?
I had a late 90's v6 Nissan Maxima new rad, tstat, water pump, fan working, basically all cooling system majors were new. Would overheat, especially after a run with out stop n go, coming to a slow down or stop.
Finally changed the radiator cap, problem solved. $12.
Pressure in the system effects the performance as well.
 
#5 ·
Not sure if 2.5 similar to 3.3 fan but I just found that my fan blades spin independently of the fan motor, weird as that sounds, so that might be worth a check.
 
#6 ·
The radiator cap is new, as well as all hoses, the water pump, thermostat, both coolant temperature sensors, and many other parts. While I cannot test the fan other than by letting the engine idle, and seeing that it does come on, I suppose there could be an issue with the fan coming on too late? The air conditioner is currently empty, so I cannot use that for test purposes.

Yesterday, I drove the van to a job interview early in the morning before I started work. The interview was approximately 5 miles from home, and this was city driving. When I was about a mile away, the engine temperature gauge moved from its normal position of just under the middle tick mark to just over the middle tick mark, then crept up to just under maximum, stayed there for a little bit, then went back to normal like nothing had ever happened.

Then, after work, I drove the family to the in-laws' house, which is approximately 15 miles away, part of which involves freeway driving. When I was approximately 2 miles from home, driving in dense traffic, I observed the phenomenon again: the temperature gauge suddenly started moving up, reached the tick mark under the maximum, stayed there for maybe 30 seconds to a minute, then dropped back to normal as if nothing had ever happened.

Then on the way home, as I was getting on the freeway, I saw the temperature gauge start creeping up, but when I hit the accelerator to speed up, it dropped back to normal (just below the middle tick mark).

Whatever is causing this is seeming to become more frequent, and it never happens more than once in the same trip. It also seems to only happen if the engine started out cold. Also, at no time does the performance or noise level of the engine change.

I am going to take the van to a mechanic today for another unrelated problem, which is that on the way home last night, I lost brake pressure, and the brakes barely work. Due to the risk of being in an accident which would be legally my fault, I am not going to mess with this, and will pay a professional to (hopefully) fix it properly.

Any advice would be appreciated.
 
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