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Old 06-24-2015, 06:16 PM
CoyoteStarfish's Avatar
(Bio)diesel enthusiast
Join Date: Jun 2008
Posts: 167
2000 ML430, overheating in a strange way.

Just picked up the above vehicle for practically a song and a dance, knowing the previous owner was having issues with the cooling system and high temperatures.

So it goes like this, PO said it overheated, had a shop change the rad, fan clutch, water pump. Still overheating, so he left the car alone and unloaded it on me.

Now, I wanted to reproduce the overheat condition to get an idea of what is going on. Took it for a spirited drive around town for about 15 minutes and the temp never climed above 85-90c. With AC on.

Electric fans are operating, fan clutch sounds like it is engaging, no bubbles or pressure in the coolant system when idling cold. Cool beans.

Now I go to drive it home (about 1.5hr away), watching the temp gauge like a hawk and everything seems fine until about 45 minutes in the temp rises to about 110 suddenly, then drops to 95 within seconds, then back up to 120, then 100, then pegs at 120 and stays there. So I pull over, no discharge from the overflow. No tell-tale overheat "smell." No ticking of lifters. No post-overheat ticking or gurgling after shutdown.

Not sure what direction to go in for diagnosis. Any tips?
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Old 06-29-2015, 12:02 AM
JimmyL's Avatar
Rogue T Intolerant!!!
Join Date: May 2004
Location: Sunnyvale, Texas (DFW)
Posts: 9,673
An infrared thermometer to see if engine is really that hot next time, or if its a gauge problem......
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John
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Old 08-30-2015, 04:17 PM
dkveuro's Avatar
Sword of Damocles
Join Date: Jun 2003
Location: Here an' there.
Posts: 2,548
Possible iffy thermostat. Mercedes says "Coolant temperature in RED sector is okay as long as coolant does not overflow..... and as long as resumed driving, coolant returns to normal."....or words to that effect.

Have had bad 'stats out of the box several times. Check the lower hose is not collapsing at high rpm too.

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