Temp gauge drops??

shimric · 08-13-2006, 12:49 PM

Is it normal for the temperature gauge to drop when I rev high??

docneon · 08-13-2006, 01:04 PM

It is not normal. It sounds like you have air in the system that is preventing coolant from circulating properly.

Follow the procedure for filling the cooling system found in the BGB http://www.mr2-tech.com/bgb.htm.

You could also have a failing water pump or stuck thermostat, but purging the system is the easiest (cheepest) place to start.

Good luck

shimric · 08-13-2006, 03:17 PM

Well I have noticed air bubbles in the coolant from time to time. Didn't think it was that big of a deal.. How could a failing waterpump cause the hand to drop?

docneon · 08-13-2006, 03:50 PM

Higher RPMs will force more coolant through the system temporarily overcoming a stuck thermostat or failing water pump. Not sure where the gauge is before/after you notice the drop, mine is normally just under half way (maybe a little lower then "just", but I put in a colder thermostat). If you gauge is half or above, you are running a little warm. Nothing that should cause any harm, but not 'optimal' either.

Weasy2k · 08-13-2006, 07:05 PM

does it drop and come back quickly and frequently? or does it just fail?

shimric · 09-07-2006, 04:25 PM

It only does it when the engne isn't fully warm. I was thinking it's just that more flow at the higher rpm's is causing the sensor to drop the hand back to cold. But it goes right back as soon as it drops.

Weasy2k · 09-11-2006, 11:54 AM

i wonder if the sensor is on its way out...sounds fishy to just drop....cause that means the entire coolant system has to be say 20 deg colder in a matr of seconds...

My guess is the sensor or bleed the system...I would just buy new sensor then bleed the cooling system.

Enthalpy · 09-11-2006, 11:57 AM

I would bleed the system to start with. It's the easiest. I'm with Weasy, the symptoms should be the other way around.

Could there be voltage anomalies in your system? It might be worthwhile to make a battery voltage measurement as you rev the engine.

Jason.MZW20 · 09-16-2006, 03:21 AM

It's normal when there are hot and cold pockets of coolant in the system, usually during warm up periods. The temperature is NOT homogenous, so as it passes very quickly through the temp sender when you rev high, it shows a dramatic drop in temperature. Because of the way the MR2's coolant system is designed, there is a vast majority of cold coolant sitting in the pipes and radiator until the thermostat opens. Once it does, and once you rev high, you push that colder coolant past the temp sender, and it registers a drop in temperature. It'll obviously never register totally cold, since it's passing through the water jackets of the cylinders, and the colder coolant is now mixing with the hotter coolant, eventually reaching a homogenous temperature.

If it's happening when the car has been running for quite some time, you have another problem, but you said it only happens when the car isn't fully warm.

Gallagher005 · 09-16-2006, 02:14 PM

i had similiar problems and it ended up being the thermostat, but i'd listen to these guys they usually have all the answers

BishopTTU · 11-24-2009, 12:47 PM

Is there a sticky on how to bleed the coolant lines?

I have a temperature sender (temperature gauge sender) ready to be replaced on the intake plenum. I've been hesitant because I don't know how to bleed the coolant lines.

thoughts?

08-13-2006, 12:49 PM	#1 (permalink)
shimric OT Ruler, Thread Hijacker Join Date: Apr 2006 Location: tom's moms house Posts: 1,510 Thanks: 42 Thanked 49 Times in 42 Posts Blog Entries: 1 iTrader Rating: (1/100% )	Temp gauge drops?? Is it normal for the temperature gauge to drop when I rev high??

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08-13-2006, 01:04 PM	#2 (permalink)
docneon former 2 owner :( Join Date: Apr 2006 Location: Round 'bout Chicago Posts: 287 Thanks: 2 Thanked 2 Times in 2 Posts iTrader Rating: (2/100% )	It is not normal. It sounds like you have air in the system that is preventing coolant from circulating properly. Follow the procedure for filling the cooling system found in the BGB http://www.mr2-tech.com/bgb.htm. You could also have a failing water pump or stuck thermostat, but purging the system is the easiest (cheepest) place to start. Good luck

08-13-2006, 03:17 PM	#3 (permalink)
shimric OT Ruler, Thread Hijacker Join Date: Apr 2006 Location: tom's moms house Posts: 1,510 Thanks: 42 Thanked 49 Times in 42 Posts Blog Entries: 1 iTrader Rating: (1/100% )	Well I have noticed air bubbles in the coolant from time to time. Didn't think it was that big of a deal.. How could a failing waterpump cause the hand to drop?

08-13-2006, 03:50 PM	#4 (permalink)
docneon former 2 owner :( Join Date: Apr 2006 Location: Round 'bout Chicago Posts: 287 Thanks: 2 Thanked 2 Times in 2 Posts iTrader Rating: (2/100% )	Higher RPMs will force more coolant through the system temporarily overcoming a stuck thermostat or failing water pump. Not sure where the gauge is before/after you notice the drop, mine is normally just under half way (maybe a little lower then "just", but I put in a colder thermostat). If you gauge is half or above, you are running a little warm. Nothing that should cause any harm, but not 'optimal' either.

08-13-2006, 07:05 PM	#5 (permalink)
Weasy2k What is an MR2? Join Date: Mar 2005 Location: Vancouver, BC Posts: 8,891 Thanks: 33 Thanked 82 Times in 68 Posts iTrader Rating: (9/100% )	does it drop and come back quickly and frequently? or does it just fail?

09-07-2006, 04:25 PM	#6 (permalink)
shimric OT Ruler, Thread Hijacker Join Date: Apr 2006 Location: tom's moms house Posts: 1,510 Thanks: 42 Thanked 49 Times in 42 Posts Blog Entries: 1 iTrader Rating: (1/100% )	It only does it when the engne isn't fully warm. I was thinking it's just that more flow at the higher rpm's is causing the sensor to drop the hand back to cold. But it goes right back as soon as it drops.

09-11-2006, 11:54 AM	#7 (permalink)
Weasy2k What is an MR2? Join Date: Mar 2005 Location: Vancouver, BC Posts: 8,891 Thanks: 33 Thanked 82 Times in 68 Posts iTrader Rating: (9/100% )	i wonder if the sensor is on its way out...sounds fishy to just drop....cause that means the entire coolant system has to be say 20 deg colder in a matr of seconds... My guess is the sensor or bleed the system...I would just buy new sensor then bleed the cooling system.

09-11-2006, 11:57 AM	#8 (permalink)
Enthalpy EMS Harmonizer Join Date: Feb 2006 Location: Denver, CO Posts: 1,226 Thanks: 8 Thanked 55 Times in 43 Posts My Google Map iTrader Rating: (2/100% )	I would bleed the system to start with. It's the easiest. I'm with Weasy, the symptoms should be the other way around. Could there be voltage anomalies in your system? It might be worthwhile to make a battery voltage measurement as you rev the engine.

09-16-2006, 03:21 AM	#9 (permalink)
Jason.MZW20 Pig Snout Join Date: Jul 2006 Location: Victorville, CA Posts: 1,373 Thanks: 15 Thanked 111 Times in 102 Posts Blog Entries: 6 iTrader Rating: (2/100% )	It's normal when there are hot and cold pockets of coolant in the system, usually during warm up periods. The temperature is NOT homogenous, so as it passes very quickly through the temp sender when you rev high, it shows a dramatic drop in temperature. Because of the way the MR2's coolant system is designed, there is a vast majority of cold coolant sitting in the pipes and radiator until the thermostat opens. Once it does, and once you rev high, you push that colder coolant past the temp sender, and it registers a drop in temperature. It'll obviously never register totally cold, since it's passing through the water jackets of the cylinders, and the colder coolant is now mixing with the hotter coolant, eventually reaching a homogenous temperature. If it's happening when the car has been running for quite some time, you have another problem, but you said it only happens when the car isn't fully warm.

09-16-2006, 02:14 PM	#10 (permalink)
Gallagher005 Watermelon Smasher Join Date: Mar 2006 Location: Arizona Posts: 566 Thanks: 10 Thanked 3 Times in 3 Posts My Google Map iTrader Rating: (1/100% )	i had similiar problems and it ended up being the thermostat, but i'd listen to these guys they usually have all the answers

11-24-2009, 12:47 PM	#11 (permalink)
BishopTTU Red Raider in ATX Join Date: Sep 2007 Location: Austin, TX Posts: 93 Thanks: 9 Thanked 2 Times in 2 Posts iTrader Rating: (2/100% )	Is there a sticky on how to bleed the coolant lines? I have a temperature sender (temperature gauge sender) ready to be replaced on the intake plenum. I've been hesitant because I don't know how to bleed the coolant lines. thoughts?