Fuel Thermostat leak causing air in the fuel line?
 

Just installed a greasel kit in my 84 190d and there is a ton of air bubbles in the fuel line. I noticed the Thermostat is leaky and am wondering if this may be introducing air to the system. I'm not sure if the hoses are hooked up properly on the thermostat to begin with. It it has several hose outlets on it, unlike the straightforward 2 outlets on the 123/124/126 chassis'. Any advice?

A leaking thermostat won't cause air in your fuel lines. They are two totally different systems. If you just put in your veggie system it may take a while to purge all the air out. I had to drive more than 100 miles to get all the air out of my veggie system. Check and tighten all your hose clamps and then drive it some and see if the air purges out.

No, a leaking fuel thermostat on a W124 WILL cause air to enter the system, and the heater and thermostat are on the suction side of the lift pump. Common problem, along with all the hoses getting holes in them with age and exposure to biodiesel and veggie oil after 20 years of soaking in diesel fuel!

Usually only the o-rings, if you can get it apart. Replace all the hoses while you are at it.

Peter