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 Vn V6 Series 1 Overheating - replaced everything... no leaks and still running too hot  

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sirskid
  • sirskid
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  • Member No.: 39,669
  • Joined: 8-January 06
  • Posts: 290
  • From: Australia
Post #1 post 8th November 2010 - 05:06 AM
hey guys i have a vn v6 that has been mechanically looked after all its life and last week it overheated on me. so on the weekend i changed the thermostat, thermostat housing, rear pipe, radiator, radiator pipes, tranny cooler pipes and water pump all with brand new parts, flushed the system with proper flush crap and put new anti-boil coolant in, changed the oil and oil filter and there are no leaks anywhere, coolant or oil.

and it's still running up to and over 120 degrees C, even with the thermo bypass switch i installed running from start up. i ran the diagnostic on the ecu and it came up 12 (system fine)

but the water temp warning light on the dash flashes at me sometimes, so i'm thinking maybe dodgy ECU water temp sendor??? but would this actually cause it to run so hot?
i also have a couple of small dings in the exhaust due to speed bumps and fat mates, could this be restricting hot gas expolsion and heating the engine from the rear???

I'm not new to mechanics but this has got me stumped.... when she cools down i'll check out the wires from the ECU water temp sendor and check that the continuity is okay, but i still can't see how that would make it run so hot.

so i'm asking what you guys think? possible causes/solutions. any input would be greatly appreciated as i'm not ready to give up and give it to a mechanic.
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lil_bobby_260
Post #2

Done a compression test or anything to see if it might have a head gasket issue? Have you pressure tested the cooling system? If youve touched wiring for the fans, theres no way they have been wired up reverse polarities (ie trying to push air back through the radiator towards the front, instead of pulling air through)?
Have you put a hand on the front of your radiator while running to see if there are any hot/cold spots?
Just grasping at straws really but thats all i can come up with.

Wraith
Post #3

Ok first thing you should check. When it get's hot is it actually getting hot? Can you hear the water being close to boiling point. The gauge sender can some times become faulty and give a false reading.

If it is getting hot then another suggestion. Is it using any coolant? Some times the inlet manifold gasket can leak and cause coolant to enter the intake ports. The only sure sign it's doing it is if coolant is dropping.

boot_it
Post #4

QUOTE (sirskid @ Nov 9 2010, 12:06 AM) *
hey guys i have a vn v6 that has been mechanically looked after all its life and last week it overheated on me. so on the weekend i changed the thermostat, thermostat housing, rear pipe, radiator, radiator pipes, tranny cooler pipes and water pump all with brand new parts, flushed the system with proper flush crap and put new anti-boil coolant in, changed the oil and oil filter and there are no leaks anywhere, coolant or oil.

and it's still running up to and over 120 degrees C, even with the thermo bypass switch i installed running from start up. i ran the diagnostic on the ecu and it came up 12 (system fine)

but the water temp warning light on the dash flashes at me sometimes, so i'm thinking maybe dodgy ECU water temp sendor??? but would this actually cause it to run so hot?
i also have a couple of small dings in the exhaust due to speed bumps and fat mates, could this be restricting hot gas expolsion and heating the engine from the rear???

I'm not new to mechanics but this has got me stumped.... when she cools down i'll check out the wires from the ECU water temp sendor and check that the continuity is okay, but i still can't see how that would make it run so hot.

so i'm asking what you guys think? possible causes/solutions. any input would be greatly appreciated as i'm not ready to give up and give it to a mechanic.


ok just some thing 4 u to know

1... all v6 engines up to vy the thermo fans wont switch on till 106.c .,.. now if u have the rad cap off the cooling system will boil over... if the car is overheating is there still a airlock in the system are the fan switching on ..... has the water pump still turning ie not siezed ... is the water pump fairly new does it still have the blades on it still .....is the radiator blocked this will also cause overheating ...... is the thermo fan comming on ....has it blown a fuse...has it siezed ....is the radiator cap holding pressure...these things you havnt told us about......

how do u know the engine is getting up to 120.c ???? temp gun????scan tool????
sirskid
Post #5

i took the cat converter off today to reduce back pressure, left the thermo fan off, re-routed the heater hose straight back into the engine and held my hand on the top radiator hose and waited while it idled. and after quite some time due to the above additional elements i felt the hot water start getting released into the radiator popped round to check the temp gauge and it was at 115 C, and boy did it feel like it. so pretty sure i have a dodgy brand new thermostat (which stupid me forgot to check before installing)

so the new 81C (compared to the stock 92C) is on the way and i now have the fun job of removing the throttle body and thermostat housing again, aswel as the fresh gasket goo i so carefully applied.

fingers crossed it works.
lil bobby, double checked the fan and it's running the right way and the heat was pretty evenly distributed accross the radiator and started getting cooler as my hand got near the outlet pipe.

wraith, it is definately getting hot, you can feel it standing near it and its a new gauge sender that i tested in boiling water that read right on the money. as for the using coolant i'll have to drive it to and from work a few times before i can know the answer to that. not really game to do that untill the new thermostat is in.

thanks for the input guys, it was nice to ask a question on here and not have kids suggesting i hit it with a hammer.
i'll post up the result in case anyone else searching something like this.
once again, thanks guys.

Wraith
Post #6

Should of kept the standard temperature thermostat. A colder thermostat won't do much except push the engine out of it's peak efficiency range.

sirskid
Post #7

i've still got the old one...in the bin that is. i tested it in boiling water and it didn't open at all. i went for the cooler option after doing an awful lot of research and talking to several mechanics. see, i live in brisbane and it's summer. it cannot run cool. i did the idle test last night and everything was good though i think my gauge is reading 10C over. about to take it for a drive and see what happens.

sirskid
Post #8

hmmmm okay the temp is now stable but that stupid temp warning light on the dash is still flashing. and the car is shifting at 2800rpm. when i put the foot down to test it it didn't smell good, like the tourque converter wasn't felly engaged or something. so i tested the resistance of the ecu temp sendor and it's fine. time to now test if the circuit is complete. if it is then it would have to be the computer right? which are about $50 off ebay.

sirskid
Post #9

circuits are good from the clip on the back of the sendor to the clip onto the ecu, then i put the multimeter on the according pins on the back of the ecu and got nothing. i'm no computer guru, but a circuit should be a circuit wether through a wire or on a board. so maybe the ecu has died. does this sound likely to any of you?

sirskid
Post #10

okay new ecu went in today aswell as a home made agi pipe cold air intake and everything seems to be running well. flogged it for about half an hour and there were no bad smells or heating issues, didn't lose any coolant either. don't want to get ahead of myself, but i think it's fixed smile.gif

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