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I have a 2003 Mitsubishi Galant with a 4g63 SOHC 2.0l engine. I have noticed that when at highway speeds the heat gauge drops almost close to C indicator and if I accelerate hard I get a burning smell from the air vents. I see no reduction in oil or coolant. Also the engine runs at optimum temperature at normal city driving and no burning smells.

What can cause such a behavior? I have read that a stuck open thermostat would behave the same way as well. But is this true? Also, I have closed 3 leaking cores in my radiator if that has any effect on this. I have scheduled a test run with Mitsubishi, but that's in a few weeks and am afraid if the issue is a critical one to drive around.

Any idea on this is very much appreciated.

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You have a clogged radiator. The fact that you've closed three leaks in the core is indicative of a bad radiator. A stuck, open thermostat would not produce this scenario because the thermostat is supposed to be open at highway speeds.

The burning smell through the vents indicates potentially serious damage to your engine. The head temperatures are climbing much too high, while the temp. indicator gauge is starved of coolant and, ironically, drops to "C". The excessive heat is burning oil, plastic, wiring, etc. in the engine compartment. Meanwhile, the internal metal parts of the engine are over-expanding, warping and wearing.

By the way, the 2003 Galant did not have a 2.0l engine option (only 2.4l). The 4g63 engine was used in early 1990's-era Galants, so you may want to check your specifications.

The dealership is the most expensive repair option. Once you've verified your car's make, model, year and engine size, go to rockauto.com and order the radiator yourself. Call local shops, tell them you have your own radiator, and ask how much to install it. I have cut the cost of repairs by 1/3 using this method. You can also verify that the total cost for such a repair should be about $300 by going to repairpal.com.

  • Thanks a lot for the response. To clear the confusion, I am in Sri Lanka, and the Europe and Asia/ Pacific/ Australia regions had a 4g63 2l variant till 2003 along with a 2.5l vt6 twin turbo version. I will check on what you have mentioned and look into this matter asap. – Hasitha Shan Aug 27 '18 at 13:52
  • to add, the burning smell is not consistent..it only comes during rapid acceleration and cruising, the smell goes away. – Hasitha Shan Aug 27 '18 at 13:55
  • Hi, I took the car to my motor mechanic, he took a look and gave some diagnosis, 1. tapet cover was a bit lose and oil was slightly leaking 2. the ac reciculating button does not close the vents properly so any smell in the engine enters inside 3. the previous owner has removed the thermostat and the engine was being constantly cooled wihtout being regulates after that, 1. installed a new thermostat 2. tightned the tappet cover did not attend to the ac re ciculating issue as the dash needs to come off. now need to test run on the highway and check the temp gauge and for smells – Hasitha Shan Aug 31 '18 at 11:35
  • Thank you for the feedback. You have obviously found the problems. Good luck with the repairs and be sure to keep us posted! – Carguy Aug 31 '18 at 16:05
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You should check the coolant temperature sensor and its wiring. If the heat gauge drops, it looks like there's a fault there. As for the burnt smell it may be a consequence of it (fan not actuated, etc.)

  • Welcome to Motor Vehicle Maintenance & Repair! Nice answer! I'd disagree that this needs to be a comment: comments are actually for improving the question, whereas this does directly address the question. – Cullub Aug 22 '18 at 12:17
  • I will look into this too. I ave read that it can be the fan belt wearing off at high accelerations. thanks alot for the answer – Hasitha Shan Aug 27 '18 at 13:53
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I took the car to my motor mechanic, he took a look and gave some diagnosis,

  1. tapet cover was a bit lose and oil was slightly leaking
  2. the ac reciculating button does not close the vents properly so any smell in the engine enters inside
  3. the previous owner has removed the thermostat and the engine was being constantly cooled wihtout being regulated after that,

So the mechanic,

  1. installed a new thermostat
  2. tightned the tappet cover did not attend to the ac re ciculating issue as the dash needs to come off.

tested the car on the highway and seems the issue is resolved.

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