these radiators are made of plastic and aluminum.the aluminum tubes will shrink over time and temperature cycles and the tubes will not flow enough coolant.[6-9yrs]diesels also run cooler than gas engines [the higher the compression the less waste heat] so if you are getting hot you have a big problem not a small one.water pumps can only leak to cause a problem with the exception of a couple of bmw's that had a plastic impeller. david poole european performance dallas tx.

I fully understand the cutaway views and the flow pattern. It's agreed that some of the flow will go down the bypass and return to the head, rather than head off to the radiator.

My premise is that the flow is increased significantly without the restriction of the thermostat, and the loss of flow to the bypass still results in more flow to the radiator than would otherwise be the case with the thermostat installed.

I'll be the first to admit defeat if someone would overheat without a thermostat installed, and, then reinstall the thermostat and have the engine perform properly.

I pulled the thermostat on the advice of a friend who is an engine builder... not a mercedes guru so i'm not saying what i did helped at all, but it was a test. as far as how the car ran without the thermostat... it was about the same. i had the same problem with the thermostat as i did without it. I think the reason for the boiling over was the fact that i stoped. I was running very hot up the hill. and decided to stop at the top to letting the car have a rest. and after i turned off the engine is when the cap poped and it started to boil over... i let it sit for a while and walked around. after it stoped boiling I saw the sign that said "6% Downgrade next 7 miles"... so i started the car... still very hot and let it roll down the hill. that stoped the heat issues. for a while. that is the only tile i've over heated.

I have orderd the waterpump. so i think i will change it.

David, The radiator is looking old... i'm not sure how else to put it, but the plastic looks old and the aluminum looks old... oxitation maybe. there is nothing wrong with it.. no leaks, but based on what you said, and the fact that i think the radiator looks old. i wouldn't be suprised if the radiator is at falt.

__________________

That's what you're missing, my friend. The flow is very slightly increased with less restriction from no thermostat but heat rejection is significantly reduced from the radiator because flow is reduced. The MB thermostat has 2 movable gating valves, not 1 like most domestic stats we may be more familiar with. Flow is increased in proportion to impeller speed, although not strictly linearly. Flow restriction is proportional to the square root of the pressure drop and inversely proportional to the flow.

In other words, if you want to double flow, you can do it by increasing pressure by a factor of 4 (2x2) or cutting the restriction in half. Getting a cleaner radiator (inside and out),and keeping a good impeller running fast (check the belt tension) will help cool the engine. Decreasing coolant flow through the radiator by removing the thermostat won't help because coolant needs to be forced through the radiator.

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Sorry, Pete, but the available data proves you wrong. Diesel Giant has produced significant sucess by drilling holes in the housing of the thermostat to increase flow. The increased flow had reduced the temperature of the engine.

Others have removed the thermostat completely and never suffered from an overheat.

Clearly the flow is increased more than very slightly.

I'm trying to explain application of basic thermodynamic principles using logic and engineering concepts. I can't, and won't, compete with "she said so" proof. Over and out.

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

In my understanding, the elimination of a thermostat will significantly increase the flow of the fluid all around the cooling system thus decreasing the temperature and takes a longer time to warm the engine up to its normal operating temperature. But, since the fluid continues to freely circulate all the time, with long period of hard driving, uphill, or stop and go traffic, with the AC on, and the condenser hot temperature is contributing to the increased temperature of the radiator at hot summer temperatures, then all the fluid that is circulating will become way to hot. This boiling hot water will not cool the engine anymore and will result to a high water temperature gauge reading.

On the other hand, if there is a properly working thermostat in the cooling system, the thermostat is giving the radiator a chance to efficiently do its job to cool some hot fluid. In the event that the engine wants some cooled fluid, the hot water temperature in the cylinder head and engine block will trigger the thermostat to open and cooled fluid from the radiator will be distributed according to the engines demand of cooled water to keep it from going beyond the normal operating temperature, then the thermostat will shut the circulation off once again and the radiator will cool off the exchanged hot fluid from the engine.

Its as simple as fluid and temparature exchange, everytime the thermostat opens, hot fluid from engine goes to the radiator and cooled water from the radiator goes to the engine. While thermostat is closed, radiator is cooling the fluid, and the engine is heating the fluid while the fluid is cooling the engine. Then when the temperature gets too hot, the thermostat will open and the fluid and temparature exchange cycle occurs.

I know the German "over-engineered" these cars but I think it's just how simple it is. It is not rocket science and it doesn't take a genius to "over-think" and "over-analyze" how these cooling system works.

__________________
'85 300D Turbo - CA Version

Actually, it's not that simple. You've described the flow for a typical Detroit cooling system.

On the M/B, the thermostat performs two functions.

1) It allows coolant from the radiator to return to the engine.

2) It blocks off the bypass so that hot coolant cannot return to the engine and must go to the upper radiator hose.

If you remove the thermostat, IMHO, there can be more flow from the radiator back to the engine because you don't have the restriction from the thermostat.

However, there is nothing forcing the hot coolant to head into the upper radiator hose and some of the coolant will return to the engine through the bypass.

It's the contention of Pete and Roy that this return flow is of sufficient quantity to compromise the cooling of the engine, despite the increased past the point where the thermostat had previously lived.

I'm skeptical of this theorem, although Roy has demonstrated that it did cause an overheat on the SD.

I'm not sure about this but I've seen some older model Yanmar diesel tractors that is not equipped with a cooling system water pump. But whan the engine is at normal op. temp., water is moving as if it does have a water pump.
What forces the water to circulate throughout the entire cooling system such as Yanmar's? IMHO, the hot water always rises to the top and the cooler temp. water always settles at the bottom. Just like the principle of the block heater that some of the MB owners are using during the winter time. Engine is off, therefore water pump is not turning, but what makes the heated or warm water to circulate?
So, what's forcing the hot coolant to the upper radiator hose? The cooled water from the lower radiator hose that was moved by the water pump and the opening of the thermostat.

__________________
'85 300D Turbo - CA Version