Temperature gauge acting funny

[MRacer]

Seems like my car is breaking down faster than I can enjoy it...not having a fun time at all.

Has anyone experience any temperature gauge problem(s)? From a cold start on a flat surface, it take FOREVER (I mean 30 minutes) to warm up); on an incline it doesn't take long but still longer than usual. And for the first time, the gauge drop dead while I was turning. My first instinct was 'thermostat going out', but the dealer's service manager says I don't need one and that there might be something else.

 

[nsxtasy]

http://www.nsxprime.com/FAQ/Troubleshooting/SlowWarmup.htm

[This message has been edited by nsxtasy (edited 21 November 2000).]

 

[MRacer]

I went there already before I took the car to the dealer and before I posted.

 

[nsxtasy]

Sorry.

I guess you have a choice. You can either (a) ask the dealer to continue to analyze whatever they think might be the problem, or (b) tell them to replace the thermostat anyway (keep in mind, it only lists for $30, so you won't be out a whole lot of money if that doesn't fix it).

 

[nsxman]

It is not clear to me if your problem is an engine that is not warming up promptly, or a temp guage that is slow to react to increasing engine temperature after a cold start. Please elucidate.

 

[MRacer]

I always leave the car idling for at least 5 minutes or so. And with the engine cover up, I can feel the heat from the engine. But the gauge still sits at ground zero. So this rules out the chance of a faulty engine. Then it could be a faulty gauge (sounds too good to be true) but that doesn't explain how the gauge could drop from hot to cold while the car is running. All points back to the thermostat.

As 'nsxtasy' puts it, I'll replace the thermostat and see where I stand.

 

[bill]

A faulty thermostat will NOT cause the temp gauge to "drop" from hot to cold after the car is warmed up and running. What you are describing indicates a loose electrical connection between the temperature sensor and the gauge. Especially, the scenario where the temperature drops as you round a corner. I would start by checking the connection at the back of the gauge. Also remember to focus on area that was last worked on if applicable, ie if you just had your dash apart.... Then I would look at the connection at the engine temperature sensor which I have no idea where it is located. Hope this helps somewhat.

 

[nsxman]

Ach so...

Your problem may be a faulty connection behind the dash, but I doubt it.

It is likely that the temperature sender on the engine has failed. Your empirical observations point to a failure in the thermistor (a variable resistance device that responds to temperature). The resistance across the temperature sender should be 142 ohms at 133 degrees F. The resistance drops to 49-32 ohms between 185-212 degrees F.

If you have an ohm meter (a $10 radio shack unit would be fine) you can check the sender yourself.

If you have a meter, let me know, and I can direct you to where to make your measurements.

 

[MRacer]

Replaced the thermostat and everything work fine again. As for the 'dropping' temp gauge, I couldn't repro that any more so I assumed it got fixed somehow.

 

[Larry Bastanza]

The reason you cannot reproduce the "dropping" guage is that the engine is running at a steady temperature now. If the thermostat is wide open (which is usually what happens when they go bad), and you change the incoming water temperature to the engine block, the engine temperature will change accordingly. Since the water from the radiator is cooler, and the thermostat was wide open, the damn thing got cooler!! Thus the gauge dropping syndrome. When the thermostat is working properly it will actually regulate the flow quantity based on the water temperature. This is also why a bad thermostat causes long warnups, since the water is ALWAYS flowing, not good.

To see this close and personal, take a good thermostat (from any car)and put it in a pan full of luke water on the stove and heat it up. You will see the thermostat actally open before your eyes. Cool it off and it will close.

Glad to see you were able to repair it without spend alot of $$$$$$$$$$.

HTH,
LarryB

 

[Nsxotic]

O.K. I had a similar problem that I posted separately..... Mine did not drop around corners though... mine just gradually went down as I drove through the cooler than normal wind... (45-60deg) I talked to my NSX mechanic and he says that the thermostat is fine and, in fact, says that a dropping gauge is perfectly normal.. I've never seen it before! I thought the therm. was stuck open but he says that therm. will NEVER close while the engine is running. It closes when you turn the car off and will only re-open again after the next start up once it has reached the operating temp. So, in essence, being stuck open would only make for a slower warm-up but NOT make the temp drop.... He swears it's normal. I still feel weird about it cos I've never seen it before on any car and I used to live in very cold temps. Now in Fla. By the way, here's another mistake I've seen people make... They think a good test for the cooling fan to see if it is working is to just turn on the air cond... NOT true. This works on most other cars because the condenser for the air is usually located right in front of the radiator, but the NSX condensers are in the low front corners so there is no reason for the fan to turn on with the air.. thought I'd share..

------------------

Todd Arnold
http://www.geocities.com/nsxcessive/index.html

 

[Andrie Hartanto]

Todd,

I experienced the same thing on my BMW. The temp goes up and down like u described. Changed the thermostat and everything went normal )the thermostat was broken and stuck open). Longer warm up perios. And yes!! the temp does goes down even after the engine is hot.

 

[nsxman]

MRacer's experience points out the difficulty of trying to diagnose problems via email. It appears that his thermostat was faulty, but based on his observations one could reasonably reach a different conclusion. An accurate test is the methodology described by Larry Bastanza... It would interesting to know if MRacer conducted this test on his old thermostat.

In the desert Southwest, we routinely have 30-40 degree air temperature swings. After warmup, my NSX water temp. gauge is stable through this periodicity.

Maybe we have a difference of opinion in what constitutes a drop.

 

[Larry Bastanza]

Folks,

I still contend that the thermostat does not act like a switch. It is designed to expand and contract to regulate the flow of water from either circulating in the engine block or allow water to mix from the cooling system. One thing that I always liked about Honda engine design (any one) is their ability to regulate temp very well. My NSX temp gauge comes up and is rock steady at the same point regardless of what temperature outside as well as how hard I drive the car. I live in NYState and experience temps outside from 0 - 100F degrees over the course of a year and my gauge is ALWAYS EXACTLY in the same place once it is warm. A thermostat that acts like a switch cannot do this. If you examine the thermostat you will see they usually have a spring type diaphram that changes length as temperature changes. Again, put on your cooking apron and do the thermostat boil!!!

One more thing...It is obvious that the NSX has significant reserve cooling capacity. I have the Dali "Stoned Shield" on my car. For those of you not familiar with it, it is basically a screen of perforated aluminum to protect the radiator from rocks, etc. By virtue of what is does it resticts airflow to the radiator. It makes absolutely no difference in the runnung temp of the car, even in the hot summer.

Food for thought....

LarryB

 

[Nsxotic]

I have the ston'd sheild also... I agree with you about the thermostat.... could my mechanic just be plain wrong that it is normal for the gauge to drop? It drops all the way to the bottom if I don't stop at a light for a while. Once I do stop, without the wind rushing through....the gauge goes right back up to normal operating position.. oh well, I think I'll just change the therm. anyway.

 

[Lud]

Originally posted by Nsxotic:
could my mechanic just be plain wrong that it is normal for the gauge to drop? It drops all the way to the bottom if I don't stop at a light for a while

Yes, he is wrong. That is a textbook case of a bad thermostat.

 

[dswartz]

As LarryB pointed out, the thermostat does open and close periodically to regulate the temperature. With a good thermostat, the temperature will remain constant regardless of driving conditions or outside temperature. As Lud said a dropping temperature is a sure sign of a bad thermostat.