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| Engine temp gauge changing with idle http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=51051 |
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| Author: | Big Montana [ Mon Mar 15, 2010 10:28 pm ] |
| Post subject: | Engine temp gauge changing with idle |
So I established that my thermo must be bad because the needle doesn't go past the 152 mark (3/8th up). Yesterday, after the rig was already warm, I parked at my parents for about 20-25 min with the engine running (I got stuck inside talking) When I came out, the temp had gone up to half way. As soon as I began to go down the road, the temp went back down to 3/8ths. Now I don't think I'm stupid. I understand the idea of air flow once the rig is in motion... I understand that the water pump would be spinning faster and moving more water but... Does this seem normal? I figure that if the thermo is stuck open, would it really still heat up to half? We just had a heat wave here (it was 10 degrees above freezing Woooo WHOOO!!!), so that could have helped. Could such motion of the temp needle be an indication of a larger problem? |
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| Author: | LibertyFever [ Mon Mar 15, 2010 10:33 pm ] |
| Post subject: | Re: Engine temp gauge changing with idle |
It might be possible that you have the wrong or a malfunctioning thermostat. I discovered that problem in my YJ but only after replacing the water pump a couple of times. My Liberty once developed a problem where it would overheat when idling. That problem turned out to be a bad clutch fan. let us know what you discover... |
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| Author: | BVCRD [ Tue Mar 16, 2010 8:23 am ] |
| Post subject: | Re: Engine temp gauge changing with idle |
Sounds normal to me. |
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| Author: | RJM [ Tue Mar 16, 2010 10:33 am ] |
| Post subject: | Re: Engine temp gauge changing with idle |
Appears to be doing the oppisite of what it should. at idle it should run cooler and when under load should be heating up. This is not normal. x2 on the malfunctioning thermo. |
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| Author: | linewarbr [ Tue Mar 16, 2010 11:31 am ] |
| Post subject: | Re: Engine temp gauge changing with idle |
x2 on malfunctioning thermostat. On a diesel, temp should go down at idle and up while driving due to its thermodynamic efficiency. Either the thermostat is malfunctioning, or your viscous heater may be twerked so that it operates at idle but not while running. Check the fuses for the viscous heater before ordering a thermostat. |
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| Author: | ac5501 [ Tue Mar 16, 2010 11:37 am ] |
| Post subject: | Re: Engine temp gauge changing with idle |
X3 on possible defective thermostat. Also. I don't know if this applies to today's engines or diesels at all, but.... In past cars I've owned, if the coolant level got too low, the temperature started to get hot when idling. Then go to a more normal temp when driving down the road. |
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| Author: | linewarbr [ Tue Mar 16, 2010 11:52 am ] |
| Post subject: | Re: Engine temp gauge changing with idle |
Hmmm, good call. Low coolant or maybe a partially-blocked coolant line? Say, at the EGR cooler? |
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| Author: | BVCRD [ Tue Mar 16, 2010 12:23 pm ] |
| Post subject: | Re: Engine temp gauge changing with idle |
My thinking was/is that if it is sitting , and no air is moving except what the fan forces through the radiator, it is at it's hottest. Only when moving and air flow is increased will the temp go back down. |
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| Author: | linewarbr [ Tue Mar 16, 2010 1:09 pm ] |
| Post subject: | Re: Engine temp gauge changing with idle |
That is how a gasoline engine works. More of the energy (BTU's) inherent in a gallon of gasoline is expended as waste heat in the combustion cycle in comparison to a diesel. Also, because of the mixing of air and gasoline prior to combustion - as opposed to air and fuel being introduced seperately at different parts of the combustion cycle, as in a diesel - gasoline engine management systems are restricted in their ability to control the fuel ratio in individual explosions of the air-fuel mix. A gas engine cannot run too lean on fuel or it will stall - which means that more fuel is causing more heat at idle. In a diesel engine management system, very little power is required at idle. Therefore, at idle, a diesel uses very little fuel and so produces very little heat, while at WOT it is using an optimized level of fuel based on intake air, and more produces more heat - much of which is released in the exhaust. That is why EGT's are of such concern to diselers that do a lot of heavy towing. The engine management system sends more fuel in answer to your right foot's request for more power. More fuel = more heat. |
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| Author: | Big Montana [ Tue Mar 16, 2010 11:16 pm ] |
| Post subject: | Re: Engine temp gauge changing with idle |
Thanks for the input guys. My thermo is original, so it could be going. I have heard of the fan clutch being a prob though, so I was currious about those symptoms. My engine has made loud fan noises a few times the last two weeks as I first start up and drive from a parking spot. I have no idea why that would have started. It has been a little warmer, but the snow has been off of the ground for less than a week. I'm guessing that it's the fan. It goes away after a few minutes. |
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