hey lady's and gent's, it's been a while since i've been on here, but i have a conundrum that i simply cannot figure out.

okay, so a while back i had a check engine light--thermostat, i replaced it and filled up the coolant and the check engine light went away (NON-OEM thermostat). next, i decided to swap the spark plugs--i went with denso 5353 iridium (I believe im getting better throttle response IMHO; but it could also be that i'm burning more fuel) while i did the plugs, i also decided to pull the trigger on a VOLO chip (a device that splices into your ODBii that is supposed to increase fuel efficiency--i did it because a potpourri of people said that they had better throttle response: and i do agree. in combination with the plugs, i get way better throttle response around the 2.5K-2.75K range.) plugs went first--no problems. next came the volo chip-- i didnt unplug the battery and blew fuse 22: 15amp (diagram said "engine electronics"). i went out to buy another fuse; swapped it, then checked it later on in the day--it was blown. like an idiot i plugged in a 25amp just to see if the check engine light would go away but instead it blew fuse 73. i checked most of the fuses thoroughly but only glanced at the fuses under the windshield--go figure it was one of those that was blown. i call around to a couple shops (my fuse 22 is no longer conducting electricity: i plugged in a 5amp thinking it would blow and it didn't) and the shop told me that that the fuse either relays to another fuse and i blew that one or i shorted out the motherboard on the car . at this point i'm thinking it's the motherboard because i didn't see any other blown fuses. so i take it to mercedes benz and they spend 2 hour of inspection (400.00) only to tell me it was FUSE 73!!!! the car is almost back to normal, now but the car over heats when i'm at higher speeds. the car is fine at idle, and driving on the streets--i even redline the car when i'm on the street and it doesn't overheat. i don't have any check engine lights, coolant levels are good, cooling fan comes on at running temperature i have no clue what else it could be... but here's the kicker part!!!! when i get on the freeway, the temperature spikes all the way to the top (120ish degrees) within seconds--2 seconds, HOWEVER when i turn the heater on (NOT EVEN FULLY BLASTED--76-80 degrees) the temperature drops back down to normal within SECONDS--2-3 seconds. so I'm thinking there's a problem with a thermometer somewhere in the engine bay? the cluster is fine, cause everything else in functioning properly?

does anyone have any suggestions? this is driving me crazy. i've been trying to use deductive reasoning to figure it out, but i have hit a wall. i am not, in any way, shape of form a mechanic, but i do enjoy working on my car and figuring things out on my own.

thank you MBWORLD!

any help or suggestions would be much appreciated !

 

I would be looking at exchanging temperature sensors. Some one on site may have a drawing.

Maybe the non OEM thermostat is not up to scratch but the sudden temp. changes may rule this out.