# How to determine if car is actually overheating or not



## Christian360 (Sep 17, 2016)

Title may sound weird..lol but I am kind of stumped here on this one.

I am not sure if my newly purchased '93 Altima is actually over heating or if the gauge or sending unit just went bad.

Is there a way I can check this with a cooking thermometer or infrared laser thing? I don't know what the temps should be or proper way to go about this.

*Here is the list of why I am confused on if it's overheating.*

1. It had no signs of it over heating at all on the trip home with it..BUT that drive was on the highway and at night so with no sitting for long periods etc.

2. The first sign of it over heating was the day after I cleaned the engine bay..AND the same day I gave it throttle via the linkage to keep it running as it was wanting to die (separate issue)...AND the first day I had to have it sit for any period of time running...so triple whammy.

3. Thermostat was recently replaced (genuine Nissan) but I took it out and tested it in pan on stove..worked fine.

4. Compression reading is good (183, 178, 183, 180)

5. No signs of steam...no bubbles in coolant..no milky oil..coolant looks like new and nothing out of tail pipe.

6. All radiator hoses feel hot including radiator..and seems to have good amount of pressure on the hoses when running.

7. Even after the car sits for five hours in middle of the night..once I get in and drive two-three blocks the gauge reads in the middle and warm air comes out already..odd but maybe normal on these cars? It's been so long since I drove my 96 I cant recall on time it took to warmup..but this is SUPER fast compared to either of my trucks.

8. The fans do kick on but only after the gauge reaches the H line..I let it do this once just to test as I watched under the hood for signs of over heating and saw none.

9. The gauge seems to stay in the middle during the evenings and if not sitting for long periods of time...fast food would be a problem (ouch..lol) but in the day the gauge will go up to the H line when driving in the city.

10. After driving and parking I hear the metal ticking as it cools...another thing that may be normal..I just don't know.


I guess that's about it...lol

Oh I also bled the system via the bolt under distributor already.

Thank you for your time reading this...I really hope I can get this figured out so I can have a nice commuter car again.


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## rogoman (Dec 16, 2004)

A good way to diagnose your coolant system is with a noncontact infrared thermometer such as the Raytek Raynger ST that measures heat energy radiating from the thermostat housing; the Raytek is available from Ebay. An ordinary contact thermometer relies on surface conductivity to take a temperature reading. Consequently, it is slow and may not give an accurate measurement if there is poor contact between the thermometer and thermostat housing. But a noncontact infrared thermometer does not rely on direct physical contact. It measures infrared heat energy radiated from the thermostat housing and gives you instant results. Note: The accuracy of an infrared temperature reading depends on the reflectivity (emissivity) of the surface. Using a noncontact infrared thermometer also eliminates the danger of coming into contact with hot surfaces, high voltage plug wires or moving parts such as fans, belts or pulleys.

To check the opening temperature of the thermostat, aim your infrared thermometer at the thermostat housing as the engine warms up. The thermostat housing will rise in temperature as the engine heats up. When the thermostat opens, the temperature will level off. If the thermostat checks out okay, make sure the cooling fan is coming on when the coolant temperature reaches 220 to 240 degrees F. No fan would tell you there is a problem with the fan motor, wiring harness, relay or coolant temperature switch.

If the fan is working properly but the engine is still running hot, scan the entire surface of the radiator to check for clogs. Temperature readings should decrease evenly from one side to the other on a crossflow radiator, or from top to bottom on a downflow radiator. If you find an area where there is an abrupt temperature change, the radiator is plugged and needs to be flushed, cleaned or replaced.


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## Christian360 (Sep 17, 2016)

Thank you very much for this..now all I have to do is go to storage tomorrow and find my laser looking thing (infrared thermometer).

If you have any other tips on where to check temps for and what temps are o.k. or bad please let me know.

I will probably be shooting that infrared thing all over the place knowing me...lol but I will write down my findings and report back tomorrow (hopefully).

Thanks again 




rogoman said:


> A good way to diagnose your coolant system is with a noncontact infrared thermometer such as the Raytek Raynger ST that measures heat energy radiating from the thermostat housing; the Raytek is available from Ebay. An ordinary contact thermometer relies on surface conductivity to take a temperature reading. Consequently, it is slow and may not give an accurate measurement if there is poor contact between the thermometer and thermostat housing. But a noncontact infrared thermometer does not rely on direct physical contact. It measures infrared heat energy radiated from the thermostat housing and gives you instant results. Note: The accuracy of an infrared temperature reading depends on the reflectivity (emissivity) of the surface. Using a noncontact infrared thermometer also eliminates the danger of coming into contact with hot surfaces, high voltage plug wires or moving parts such as fans, belts or pulleys.
> 
> To check the opening temperature of the thermostat, aim your infrared thermometer at the thermostat housing as the engine warms up. The thermostat housing will rise in temperature as the engine heats up. When the thermostat opens, the temperature will level off. If the thermostat checks out okay, make sure the cooling fan is coming on when the coolant temperature reaches 220 to 240 degrees F. No fan would tell you there is a problem with the fan motor, wiring harness, relay or coolant temperature switch.
> 
> If the fan is working properly but the engine is still running hot, scan the entire surface of the radiator to check for clogs. Temperature readings should decrease evenly from one side to the other on a crossflow radiator, or from top to bottom on a downflow radiator. If you find an area where there is an abrupt temperature change, the radiator is plugged and needs to be flushed, cleaned or replaced.


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## Christian360 (Sep 17, 2016)

Ok..so I finally found my infrared thermometer and have some results..plus a little more info / questions.

Today was a semi warm day here (as warm as it gets this time of year anyway) and I took the car on the highway for 16 miles then up a hill for five miles to let it get as hot as I could before checking the temps.

By the time I pulled over the temp gauge on the cluster was almost pegged...
the fans had not come on yet though..
and when I took off the radiator cap (as soon as I pulled over) it did actually release a lot of pressure and coolant came out...(kids don't try that at home..lol) 
I have not done this in so long that I don't remember if this is totally normal or not on a car that's been running for awhile or if this is a sign of over heating.

And here are the temps...

Top of valve cover from left to right next to each plug.
173, 157, 155, 170

Radiator hose outlet (left hose)
194

Radiator hose inlet (right hose)
180

Shorter hose next to inlet (not sure what this is yet)
184

Radiator cap
194

Engine head, left side directly above exhaust heat shield and just under valve cover
281

Engine head, right side directly above exhaust heat shield and just under valve cover
267

Unfortunately I forgot to take a water temp reading this time..but the first time I did these readings when the temp gauge was almost to to H line it read 172

Also some more info to add...

After it sat for an hour or so I took the clip off the temp gauge sensor and the fans immediately kicked in as they should..they also work with A/C on..and they have come on before when the temp gauge was pegged...so I am assuming these work properly.

BUT what I found kind of odd..and again maybe this is normal but when the clip is unhooked form the sending unit my temp gauge still reads right in the middle like where it should be after driving all day...I would think that it should go to it's lowest point...so wondering if this is a sign the gauge itself may be bad?

I know this is a lot to read but I really want to figure this out so I can start making this my daily driver without constantly fearing I am going to over heat the engine and after doing so much research online I see others with similar problems so maybe this can help them or others in the future.

Thanks for reading and as always input is appreciated


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