'83 500SL Thermostat Location

[meltedpanda]

Oh I see Then yes id say it could be the port. Can you soak it in parts cleaner

[Diseasel300]

I think my next step is going to be to remove that casting and boil it out in some dilute citric acid to get anything and everything in that port cleaned out. I know the water pump is working, the radiator doesn't have any symptoms of being blocked, and the thermostat is new.

It just reeks of an airlock to me and I keep focusing on that burp port as my culprit. Since that thermostat sits up on top of the engine, and the block is higher than the radiator, it seems logical (to me anyway) that if that port is blocked up with scale or something that the thermostat will be airbound.

[Diseasel300]

Invested some time in the car this evening (and made a HUGE mess on the warehouse floor, but that's another story).

The thermostat housing is clear and clean. Burp port is free and the little ball is freely rattling. I went ahead and boiled out the housing in citric acid just to make sure it's spotless.

Moving on, I pulled the radiator and gave it a good flush. Good flow and nothing but water and coolant came out of it. No rust, no corrosion, no flakes, no calcium. Fins are straight and the A/C condenser is clean.

Starting to run out of options, I decided to test the thermostat by throwing it in a pot of boiling water. Before I tossed it in the pot, I attached a thermocouple so I could monitor temperature. I think we have a culprit... I measured 97˚C on the thermostat body, and it was only open ~1mm. I left it in the pot at full rolling boil for ~10 mins, the temp on the body was 100˚C and still no further open. We're talking a gap barely big enough to get a fingernail under. I don't think that's right for an 84˚ thermostat...

Ordering a new thermostat and trying again. Shame, it was a Wahler too.

[Diseasel300]

New thermostat came in yesterday evening, it's a Mahle/Behr compared to the OEM and replacement Wahler. New one is wide open in boiling water, and still cracked open ~2mm at 84˚C. Big big difference from what the "new" Wahler is doing. In the same pan at the same temps, the Wahler is barely open. Fingers crossed this cures the overheating. We'll know this weekend.

[Diseasel300]

Just to wrap up and close out this thread:

The Mahle thermostat works fine, but the temp gauge on the dash still showed the car was overheating. It would climb up to 110˚ and stay there, then lazily come down, then go up, etc. Problem is that the temperature of the water outlet to the radiator hose was nowhere close to that. I started tapping the temperature sender with a screwdriver handle while having a buddy watch the dash, and the temperature would move around as I struck it. One new temperature sender later and it seems all is back to normal. I put 40 miles on the car today and the needle was in the middle or slightly below the whole time.

[meltedpanda]

I like happy endings