103 engine 300E bleeding cooling system?
 

Hello


My 1987 300E does not have a bleed screw in the top of the thermostat housing. To bleed the cooling system there is a bolt on the top of the head.


I understand that the housing was updated with threaded hole and bolt / crush washer..


I am not sure which point is higher, the bolt in the head or the screw in top of the thermostat housing?




Why and when was the screw added to the thermostat housing?


I will soon be replacing my thermostat and was wondering if I should change the housing to the updated part while I am at it?

While I assume the original method would work fine, it's <$30 from the dealer to get the updated housing and banjo fitting, plus you'd need some hose for the line that goes across.

my setup is a bit different, there would be no fitting for a hose that goes across. the updated part just has a threaded hole in the top of the housing that has a bolt and washer, the bolt is loosened and or removed to bleed the system

I just went out and looked at the vehicle, the top of the thermostat housing is about two inches higher then then bleed bolt in the top of the cylinder head

The screw plug in the top of thermostat serves 2 points , one, to take a sensor , 2 to help bleed the system, on my 103 it has both one on thermostat and also one on the block rail and i use them both to purge the air .I must say it is hard to get all the air from the system. Just about to do this job again as the coolant needs changing and i am not looking forward to doing so .

Bleed from the coolant reservoir. What I have found that works amazing is to add the coolant and jumper the aux water pump. Keep adding the coolant and the aux pump will do the work in getting it circulated and pushing any air out of the system.

I still think the bleeder hose is the best option. You might need to update the coolant reservoir as well but I've never had any issues bleeding the system on my M103s.

If you're already replacing the t-stat then filling the block with coolant to the height of the t-stat will help getting it bled a little easier, though generally as long as there is a reasonable amount of coolant in the engine it will bleed without much trouble once the t-stat opens.

This is interesting .Do i need the engine running at the same time ? Can you give me more information please?. or be more specific .

No, you don't need the engine running nor do you need the car on. Just start adding coolant through the reservoir and when it starts to rise or look like its full (usually after maybe a gallon or less) jumper the aux wp pump and you'll see the coolant start to go down and you will hear it gurgling as it flows through the heater core because it's pushing the air out. You can listen as its circulating the coolant through the engine block and feel it moving through the hoses. Leave the pump running and keep adding coolant until it is full. The idea came to me when I was wiring my aux wp to use it as an aux wp :D to keep engine temps down after I shut the engine down. Usually the temps skyrocket to near 120 after driving in 115 summer heat and letting the engine sit. When I saw how quick the temps came down after shutting the engine off, I realized the aux wp really moves a lot of water within the system so I started to use it to help circulate the coolant during refills when I drained my coolant. It only takes about 5-10 minutes max. Here's a video of how well the aux wp works by quickly moving stagnant coolant from a heat soaked engine. https://drive.google.com/file/d/1ckmyET4KMGXuI8WkP5f1vSvz3muRdhO1/view?usp=sharing

Yes good idea , but i would think if the thermostat is closed then it will interrupt the flow of coolant through the system . I am interested and i will use this method just need to know as the thermostat is closed, and the water is cold in the system, will it still circulate .

Yes. The thermostat only prevents engine block to radiator, you're filling from the reservoir, the first thing you will fill up is the radiator.

ismalley well proof will be in the eating .The next time , in a few weeks time that will be after i fit my new wing . Then it will be time to do this coolant change And i will use your method ..I will then let you know just how the coolant refill goes .

Should be easy. Remember Make sure the system is all back together and everything is buttoned up. No need to turn on the car. Just start filling from the coolant reservoir and when it starts to get full, stop and jumper the aux wp and let it circulate coolant throughout system. Keep aux wp running while you add more coolant. When you reach the satisfied level, you're done.

When I changed the thermostat recently, I parked with the passenger side uphill and slightly nose up. That way, the reservoir cap is undoubtedly the highest point in the system.