240D Is getting warm - Page 2 - PeachParts Mercedes-Benz Forum

#16 08-21-2003, 01:01 PM

Before tearing into the cooling system. Get a laser thermometer and check the radiator. I've found mine to be partially plugged, and will be replacing it. With the needle at 105c on the guage, the thermometer was showing 110 - 115f across most of the front, and around 140 - 150f on the back. The tech that I was watching use this was also able to verify that the water pump was indeed circulating, and that the thermostat was opening by checking temperature all along the engine and external plumbing. It's a neat tool that will be added to my selection very soon.

leathermang · #17 08-21-2003, 01:44 PM

Subaru....
"the round part that is below the main body of the T stat.
" You mean on the ' flat' ? or something else?

Stevo · #18 08-21-2003, 02:10 PM

Greg

Ya, Sorry, I dont know how to describe it but you have the "main" part of the T stat that controls the main flow , then theres that flat round (1 inch dia +-) thin "plate" that covers the bypass hole. Drill a small hole in that.

Subaru....Oh. my daughter wants one, although she loves her 240d a Sub would more fit her needs, I was crushed at first

but i got over it

Steve

leathermang · #19 08-21-2003, 03:44 PM

yes, a little hole there can really help....

300SDog · #20 08-22-2003, 02:18 PM

"My "79' 240d was overheating last year and I drilled a small hole in the round flat part of the T stat..."

Stevo, thanks that sounds like good advice.... also way to eliminate air pocket from forming with hole pointing up. Will do this when installing T-stat after weather cools down.

Another thing I'd like to do is mainline auxilliary fan to toggle switch on console. Am also wondering if 300D or 280E radiator would hold more water. Running hot seems to be mostly 240D problem... not surprising as this car taxes its engine to the max.

Meanwhile my '79 240D stays mostly in the numbers "175" on the guage with no thermostat and no shroud.

Leatherman, your idea of shroud helping airflow when standing still makes sense..... however, it strikes me the bloody shroud actually blocks airflow when car is moving.

The damned shroud came into being at/near 1973 when they also deflated the seats on account of 'fire hazard' from flamable glue holding horsehairs together. I'm glad to be rid of it, so maintainance can be done easily - important stuff like flushing the system, checking the belts, etc.

You know me, I've got no patience for wacky over-engineered features..... and I can recite laundry list of useless items attached to an otherwise superb automobile - stuff like the idiot climate control, feeble cruise control, stupid 'engine management' systems, sensors and relays.

Stevo · #21 08-22-2003, 04:44 PM

When I rebuilt the engine for my "79' 240d I put in a new 300D radiator.

240DieselDog Did that diagram come through?

Steve

leathermang · #22 08-22-2003, 05:46 PM

"Leatherman, your idea of shroud helping airflow when standing still makes sense..... however, it strikes me the bloody shroud actually blocks airflow when car is moving. "

That is very close... The shroud is not at fault though... the fan , when turning at certain rpms,but with the car speed above certain speeds , does act as a restriction to airflow.
However, the amount of air which does cross the radiator fins should still be fine for cooling the engine even though some may be blocked outside the car and go around the radiator.
This situation is why some cars went to ONLY electric fans... and some added the viscous clutch to allow the ram air going through the radiator to push the fan past the rpm which it would have been turning due to the belt run by the engine.
If you will check out some professionals who know about air pressure you will find that the area under the front of the car, when it is moving , is a high pressure area... which means without the shroud you have air pressure in the engine area which will also be working against air going through the radiator fins...
I hope you will reconsider your decision to run your car without the shroud.

If you look around...you will find that MB is not the only company using shrouds... so it may not be " overengineering"... it may be a good design based on sound air flow concepts.
It is even more critical to have the shroud if you have an AC condensor because that adds even more restrictions to air getting to the radiator.

300SDog · #23 08-23-2003, 05:42 AM

Stevo, nope havent gotten the diagram..... why dont you post it here? It cant be any tougher to post on msg.brd... I'd like to see how the waterflow bypass system works. How much larger is the 300D radiator?? Chart of total coolant capacity says 10.5 qts. (240D) - 11.7 qts. (300D) - so it might be less than 1 pint larger, i dunno.

Leatherman, post '73 radiator shroud (standard feature on all cars) strikes me as safety device to prevent everybody from getting their fingers chopped off. It emerged about the same time they started telling crybabies NEVER to remove radiator cap when warmed up engine is idling - another myth that can be ignored by someone who knows what they're doing..... In fact you risk cracking the head by adding water, even little at a time, when the engine is NOT idling.

Without the shroud - I'm happy having full access to front engine components. Otherwise, I'd be removing and installing the bloody thing several times each year just to maintain the car..... removing thermostat for coolant flush, turning crankshaft for valve adjustment, tightening the belts, etc.

Bottom line, flushing the system twice a year with $3.99 valvoline 6 hour radiator cleaner probably does more good than all the shrouds in the world.

Btw, from what you say about air flow.... it sounds like front end spoiler would also make the 240D run cooler, but is this effect actually measureable?

JimSmith · #24 08-23-2003, 10:02 AM

240DieselDog,

Think of the shroud as a duct. It is not a safety device, and became a standard part once air conditioning became a popular option. With the added flow resistance of the condenser in line with the radiator, it became necessary to block the air flow "short circuits" that were possible without it.

I posted these excerpts from the shop manual I have for my 240D:

JimSmith · #25 08-23-2003, 10:06 AM

Here is a systme schematic showing the engine fully warmed up and under full load:

JimSmith · #26 08-23-2003, 10:13 AM

Here is a view of the system during warm-up from a cold start, showing only the area right around the thermostat:

JimSmith · #27 08-23-2003, 10:18 AM

Here is a view with the system in its normal operating mode when the thermostat balances by-pass flow and flow through the radiator to regulate engine coolant temperature:

JimSmith · #28 08-23-2003, 10:29 AM

240DieselDog,

So, the coolant system design suffers a loss of capacity when you take the thermostat out, as noted above. And the shroud is really a duct that ensures the energy being consumed to drive the engine fan actually makes the air go through the radiator and remove heat from the coolant circulating in the engine. And, in spite of what you have done to your car, it still runs within the normal operating temperature range. I think your treatments must be keeping the rest of the system operating at peak performance, which is adequate for the engine to keep its cool.

All this goes to show that from the factory these cars had excess capacity. I have noted in the past they always run at a dead 175*F, or just under 80*C no matter what the outside conditions, speed, slope of the road, etc when they are new. The fact that this changes means somewhere capacity has been lost. I am aware of the manual bold letters above saying it is ok to run just under 120*C, but I grow nervous when I see the needle on the gage off its previous invisible rest or peg. I think another good flush is in order on my 240D.

The other cars, gas powered units and my E300D TurboDiesel, have always been a little easier to get to run over the 80*C mark in stop and go traffic, especially in the summer.

Hope this helps, Jim

Stevo · #29 08-23-2003, 10:38 AM

Thank you Jim..I have company visiting and dont have time to mess with figuring out how to do anything new right now, thats just what I tried to send him.
Steve

300SDog · #30 08-23-2003, 12:59 PM

Outstanding!!! fig.3 (partial load) most closely resembles operation without thermostat.

As it stands with system wide open, combined with new water pump.... the needle hardly ever leaves the 175* range.

Old water pump seal was not shot..... but blades were eroded down to nubs. This tells me water pump efficiency can fade away unnoticed. Replaced the WP in July when the needle climbed 3/4 to redline on rare occasions. Discarded T-stat might have been shot too, have a new one in the trunk.

Had no idea the bypass plate closed under heavy load to mainline engine coolant to the radiator. This might have hurt me if mountains were nearby. I always thought it just cut off engine coolant when closed, otherwise it opened all channels.

Jim, you made a believer out of me!

Nevertheless, can understand how pulling the T-stat increases efficiency of coolant flush that I've been doing twice each year, running 95% staight H2O in Summer months, better than anti-freeze for cooling the engine.

Next month I'll pull the radiator and spray out cooling fins with garden hose and soap to atone for my errors. The shroud?? .....nah, its still a nuisance device to me. Am still suspicious of it blocking airflow at high speeds.

Dont judge me too harshly - i grew up owning primitive finbodies back in the '80s that had none of these issues.

Thanks for taking time to post the coolant flow chart - something for everybody who searches "Thermostat"...... immortalized in archives that will never be lost or forgotten.