'69 280sl Overheating

[cjpoulos]

Hey! I've been having some issues with my 280sl running too hot. I've replaced the thermostat, water pump, and radiator. I bypassed the heater core temporarily and made sure that the accessory belt was tightened enough. I've also done countless block flushes with vinegar/neutralizing baking soda flush. The car runs for a few minutes and comes up to temp, but it continues to rise up into the 230 range. I'm sure it would continue to rise if I let it. The fan spins as it should and as far as I know the whole cooling system is set up to function properly. I've tested for blown gaskets as well and we're all good there. Any idea why it may be getting so hot? The car sat for over 20 years before I bought it in June, and I figured there may be a blockage inside the block? Maybe the WRD? I've removed the (22mm?) block drain plug and flushed through it as well. This is one of a few issues I'm having, the car likes to stall at idle. Sounds like a single cylinder misfire (the car stumbles). Could be related? I've searched the forums but I can't figure it out! Thanks!

[Tom]

Couple of questions, thoughts:

On the new radiator, was it truly new or rebuilt?  Did the rebuild include upgrades like an extra coil?
Have you replaced the fan clutch?
Have you considered replacing the fan with one that has more blades (plastic, not metal)?

Bypassing the heater core will make overheating worse as, when the water flows through the heater core, it acts like a supplemental radiator.

If all else fails, consider aftermarket electric fans.  It's a tight fit but can be added.

I have a similar issue with the engine miss and stalling.  Hope someone can post a few ideas on that fix.

[rwmastel]

Would it be a proper troubleshooting step to remove the grille and use a thermo sensor gun to look for cold spots in the radiator when the engine is hot?

[cjpoulos]

The radiator was a brand new aluminum radiator. I haven't replaced that fan clutch but it seems to function properly. I rebuilt the WRD. I had to bypass the heater core temporarily as its plugged, and I'm not quite ready to pull the dash apart yet. I want to test the car after reapiring the WRD, but now I need to replace a fuel line that just started leaking!

[ctaylor738]

Somewhat of a long-shot, but are you filling the cooling system through the heater hose?  If you fill it through the overflow tank, you can get an air bubble that will prevent the thermostat from opening.

Also, for less than $30 you can get an infrared gun that will let you look for hot and cold spots.  And check out your barbecue grill!

Cheers,

CT

[AndrewB]

Are you sure your temperature gauge is correctly calibrated ?