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Old 07-11-2013, 01:54 PM   #1 (permalink)
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Default car overheats for like 20 sec, then goes back to normal

Hello.
So my suzuki reno had blown head gasket. I changed it, put new, shaved the head, put new thermostat, the cap on cooling bottle, radiator, two fans, water pump. After that it was still overheating. After that i changed the cooling temp sensor. And finally it was good. But then i was driving on highway, and needle suddenly past the middle on temp gauge, up to 3 quarters, then went back to normal and i drove after that couple month after that with no problem. No antifreeze leeaks, nothing. Yesterday same thing happend again, i heard a loud click tho from fuse box, and it started to overheat then went back to normal.
When i parked and waited the fans turn on on time but i still hear the click from the fuse box. Is it possible that the fuse or relay is nt working properly?
Because when i bring to mechanic its not overheating so he cant diagnose it.

ANy suggestions or ideas please?
Thank you
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Old 07-12-2013, 06:53 AM   #2 (permalink)
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sure *sounds* like a bad stat..
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Old 07-12-2013, 07:59 AM   #3 (permalink)
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Think about this - how long does it take for water to boil?
How much energy would it take to get an engine to "overheat"?
How much energy would it take to get an engine from "normal" to "overheat"?
How could you get that much energy in 20 seconds?
How could you get rid of that much energy quickly?

I think you'll agree that whatever the problem with the car is, overheating is a misleading description - why is this important - primarily because we're not there to see it.

Fuses are fire protection devices, they either work (allow current to flow) or don't (no current flows), there is no way for it not to work "properly", relays are nothing more than switches, switches that allow a low current controller to control a high current device, for example the ECU to turn the fan on/off, yes it is possible for a relay to not work properly - you could hear a relay click, but because of burned contacts, it doesn't switch on (or off).

As for a bad thermostat - I don't think so. My understanding of how a thermostat (on a gasoline engine) works is that it's closed (no coolant flow) when the engine is cold, and then as the coolant surrounding it warms up, it expands and starts to open (some coolant flow), and at some point when the coolant temperature is high enough, it will be fully open (max coolant flow).

Thermostat failure modes are going to be never closed, never open or never fully open - the engine is going to take longer to reach operating temperature - if it never closes, overheat rapidly (tens of minutes, rather that tens of seconds) - if it never opens, or overheat occasionally (and gradually), if it never opens fully - this last will be dictated by how the car is used.

What is it critically important in diagnosis of a problem like this, is what is the actual temperature of the engine when it "overheats" - and that may be different from what the gauge shows (dash gauges are not precision calibrated devices) - you mentioned replacing the "coolant temp sensor" - that's not going to stop from the vehicle from overheating, although it could stop the gauge from reporting an overheat condition (either actual or erroneous).

I hope you see where I'm going with this - you have presented no conclusive evidence of overheating - get yourself an IR temperature gun (something like
this this
) - check your local Lowes, Home Depot, or what have you, and use it to measure the temperature of the engine when you think it's running normal, and again when you think it's overheating - hold it about an inch away from the radiator top hose as close to the engine as you can get it.

Is the engine really overheating?
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Old 07-12-2013, 02:39 PM   #4 (permalink)
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hi thanx for reply.
When i was at mechanic he checke the temp and it was right. The fans were starting at right temperature.
And the thing is that car overheats for like 20 sec really needle passes the middle. And it happens when i drive on highway. SO there is no way for me just to stop and check the temp. I believe the fans dont turn on at that point.

Last edited by fordem; 07-12-2013 at 04:26 PM. Reason: remove unnecessary quote
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Old 07-12-2013, 04:35 PM   #5 (permalink)
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There really is no need to quote the last post in it's entirety (which is why I deleted it).

I know I said this before, but I'll say it again - there is NO evidence that your engine is overheating - I've already explained why the needle going over the mid point for 20 seconds is UNLIKELY to be an overheat condition - you're asking me to believe it heated up in the first 10 seconds and cooled back down in the next 10 seconds - it's a lot more likely that your gauge is not working properly, and if I link that with your having said that it was overheating before and you fixed it by replacing the coolant temp sensor, which as I have explained, cannot correct an overheat condition, then the probability of it being the gauge just increases - out of curiosity - did you use a genuine Suzuki sensor?

By the way - the probability of your cooling fans coming on whilst you're on the highway is almost non existent - the fans turn on, as necessary, to ensure adequate air flow through the radiator, when the car is moving forward, the forward motion itself forces air through the radiator, so once you're travelling at a reasonable speed, the fans don't turn on.
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Old 07-13-2013, 03:10 PM   #6 (permalink)
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That's a great explanation Fordem. The energy required to overheat and cool that quickly just isn't plausible in an automotive environment.

I 'believe' what causes the thermostat to open and close the way it does is a type of wax that surrounds a ball bearing. As the wax heats up along with the car the ball bearing moves, allowing the thermostat to do its designated function.

So ID have to agree that it must be an electrical, not mechanical problem.
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Old 07-14-2013, 09:57 AM   #7 (permalink)
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Have the mechanic check the coolant temperature sensor and its wiring for a possible intermittent connection or a short. The sensor itself could also be faulty, and is not terribly expensive (mine cost ~$15) so you could swap it out for a new one and test.

Our cars have 2 fans which run at 2 speeds, depending on coolant temperature and A/C operation. The speed control is via 2 relays next to the radiator on the lower frame of the car. They are configured so they run both fans in series for low speed and in parallel for high speed. Have the mechanic verify these relays are operational.

Remove the coolant reservoir cap, start the engine with the heater running on high. Let it warm up until the top radiator hose is warm and add coolant to the reservoir as needed. This will ensure the system is purged of any air pockets.

ETA: Disregard the rest of this post, but will leave it up... for justice!

The following may sound silly, and may very well NOT be the case in your, uh... case, but are the new fans turning the right way, blowing air towards the engine?

I recently worked on an Aerio where someone wired in an aftermarket fan backwards and had it blowing towards the front of the car. It would only overheat at highway speeds.

My theory is that when the car was stationary or at low speeds, it was OK. At higher speeds, the fan would work against the airflow enough to slow it down and thus overheat. ***It did NOT take just a few seconds to overheat, though.***

I rewired the fan and afterwards it was fine.

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Old 07-14-2013, 11:04 AM   #8 (permalink)
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Quote:
Originally Posted by P1NkY View Post
I recently worked on an Aerio where someone wired in an aftermarket fan backwards and had it blowing towards the front of the car. It would only overheat at highway speeds.
The only way that fan in the Aerio should have come on at highway speeds is if it's the a/c condenser fan.

Try this when you have the time - wire a couple of dash lamp bulbs (any low wattage 12v bulb will work) in parallel with the fans and mount them where you can see them - they will light when the fans turn on - and then take a drive on the high way - leave the a/c off and see if those fans ever come on.

I've run vehicles with non functional electric fans and the only time they will run hot is in heavy traffic, I've never once seen one overheat on the highway, because the forward motion forces enough air through the radiator.
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Old 07-14-2013, 11:42 AM   #9 (permalink)
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You're absolutely right, fordem; I now see the folly of my statement (I guess I AM getting old, after all! ).
I stated the car would only overheat at highway speeds, which was what the lady owner told me and I foolishly passed it on.
The reversed fan was, in fact, the condenser fan. I guess she probably only noticed it overheating while being stuck in traffic (on the highway, LOL).
Funny how she told me it didn't do it anymore? Kooky...

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Old 07-14-2013, 08:44 PM   #10 (permalink)
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Because it was the condenser fan, it would come on whenever the a/c compressor runs, so pretty much whenever the a/c runs - at low speed (or stuck in traffic), it'll probably move enough air through the radiator/condenser stack to keep things cool, even though it's fighting the draft from the forward motion, but get the forward speed up and the air flow will become inadequate, so that's when it will overheat.
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