603 Thermostat Question - PeachParts Mercedes-Benz Forum

oilslick · #1 08-23-2007, 01:13 AM

I have been eliminating a few issues on my newly aquired '87 300D Turbo. Temps have been in the upper 90's here for the past two weeks and out on the open road the car runs warmer than I would prefer, usually 100C and will creep higher at idle(no higher than 110C and all this with the A/C operating). I am not comfortable with these temps.

I have checked the fan clutch for proper operation and according to information gained through the search feature here I have ruled it out as the cause.

I had the radiator "boiled" out by a qualified rad shop. The rad tested great for airflow and coolant flow after the service but didn't solve the problem.

Aux fan works but I need to replace the 3-pole high speed switch because it is no good. Switch is currently grounded and works continuosly.

I couldn't find exactly what I was looking for so I must post this. My thought is that the t-stat is possibly stuck open or broken and the system cannot properly cool the coolant fast enough. I went out tonight and was looking around the engine compartment and squeezed the upper rad hose and could hear a clicking noise from the t-stat housing. Should I be hearing a noise from that area? I know anything is possible but could the t-stat be broken and causing the engine temps to be higher? Sure sounds like something is loose in the t-stat housing.

Kevin

Hit Man X · #2 08-23-2007, 08:36 AM

Expansion tank cap good?

oilslick · #3 08-23-2007, 08:54 AM

Brand new cap and expansion tank. Brand new!

No pressure overnight in the system and no oil visible in the coolant. Just runs too warm for my liking. Thanks for the reply.

Kevin

JimFreeh · #4 08-23-2007, 08:54 AM

If your 'stat is not opening fully, temps will reaally climb when running down the hiway at speed on a hot day. Your symptoms sound like the radiator is not rejecting sufficient heat.

Even "boiled out" radiators may not allow sufficient heat transfer.

I chased both problems you have on my 83 300SD and 300D, by swapping parts back and forth, and a new radiator was the cure.

OM617 and OM603 systems have similar flow characteristics, as the 'stat needs to be fully backseated to prevent short circuiting the radiator.

Remove the 'stat and place it in a pot of boiling water and see if it is opening up enough to backseat. I had a new one recently that failed to fully backseat, so it's possible....

Jim

oilslick · #5 08-23-2007, 09:22 AM

I will try the t-stat. I don't plan to spend any more major money on the car since I bought it to sell. I would like to be able to rule out all the lower cost items so I don't end up with more in car than I can get out of it. The rad was my first inclination that's why I had it serviced but $40 verses several hundred or more was worth a try. Maybe the new owner can try the rad

.

She hasn't gotten over 110C in all the high temps we have been having around here. She runs GREAT!!! Lots of power! High temps are giving me concern. I can cruise the interstate at 70mph with A/C on and it will hover around 100C. Stop in traffic too long and she will climb to 105C or a tad above. Turn on the heat and temp will drop noticebly. That too causes me to think it is still a flow problem but I am too dang tight to by a new rad

.

Kevin

Johnhef · #6 08-23-2007, 12:27 PM

I just put a new behr radiator in mine after one of my endcaps split, I had replaced the thermostat two years before and had a small leak from the housing ever since (pinched the seal), after replacing the seal and refilling I think I need a new thermostat again, temps run a little high, but never over 110C. coming down a mountain at the gtg back in PA earlier this year, the temp actually dropped from 80 to 60C. I've never seen one drop before!