I have a coolant leak in my 1985 CA 300D and I cant find the source. Nothing from the visibles in the engine bay, includes hoses to and around thermostat. The leak hits the pavement right below the engine block, just forward of the firewall. My engine temp popped up to 110C and I realized the reservoir was nearly empty. Upon refill the temp corrected. I have messed with the coolant system a little for a veg conversion i have not used yet, but those two joints are leakless. I replaced the thermostat 2 months ago. And the monovalve 1 month ago.

Any suggestions?