Hi everyone
my car drives me crazy , i have a 1991 Mercedes 190D 2.5 that runs hotter than normal and that causing oil pressure to drop to 1 bar in all time even it get worse on hills or when ac on
i inspected every thing even i just replaced the thermostat but nothing changed
both fans are working ,i flushed the engine and the radiator with hydrochloric acid
no play in water pump and no cracks on hoses

but there is some symptomes that i think are goin to help :

the heater isnt hot enough
and the lower radiator hose is colder than the uper one
and yes i know this is the symptome of a worn thermostat
but i juste replaced it with a new one
thats crazy
we were fine with horses why they invested cars
horses are simple and cheap to maintain

thanks alot my friends and sorry for my bad english

Are you sure the clutch fan is good? That's usually the first thing to check since it's easy to get to. What brand thermostat did you put in?

I have a 190D 2.5 that had some overheating issues until I flushed the coolant, changed the thermostat, and changed the water pump which was original at 320K miles. I haven't replaced the clutch fan yet but I have the replacement clutch ready to go.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.

Thanks my friend for your replie
i bought this car with a fan that always turn directly with engine
so i dont have any clutch
and the auxiliary fan is working great
the old thermostat has a 1year old
the new one is a Mercedes genuine one
also i replaced the coolant and flush all the system
i suspected the water pump but there is no leaks or noise in the pulley

The lower radiator hose should always be cooler than the upper hose. But if the delta T is more that 20 degrees, then the thermostat is closed or the radiator is clogged. Since you've replaced the thermostat, it's a good bet that your radiator is clogged. You can try another flush (I hope with citric acid, not hydrochloric), if that doesn't do it you'll have to replace the radiator.

One more thought. There could be debris trapped between the a/c condenser and the radiator.

thanks my friend for your replie
i flushed the radiator for 2nd time in a radiator shop
the radiator is working good
also they instpected water pump , ac condenser
and now there is slightly very tiny improvement in cooling but not sufficient to keep oil cool
you know om602 N/A dosent have an oil cooler so all the work is for coolant system . god damn Mercedes-Benz engineers
even tiny Naturaly Aspirated cars now had oil cooler

some guys in the radiator shop told to flush the engine block with their engine flushing machine

so tommorow after flushing engine block i will buy again a new thermostat
or drill some holes in thermostat like Diesel Giant

Thank you my friend
i flushed for 2nd time the radiator in a radiator shop
its working fine
they also inspected water pump and the condenser
now their is slight very tiny improvment in cooling but not sufficent to cool the hot engine oil
you know Mercedes OM602 N/A engines doesnt have oil cooler so all the the cooling work is for the great cooling system. god damn Mercedes-Benz engineers
even small cars now had oil cooler

some guys in radiator shop told me to flush the engine block with their engine flushing machine

so tommorow after flushing the engine im goin to buy again i new thermostat because 100% i have a coolant flow problem
or just drilling it like Diesel Giant

What happens when you run the engine without the thermostat?

did you put it in backwards?


What happens when you put the heat on high in the cabin when it starts getting too hot?

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Running without a thermostat should make the engine hotter, because the bypass would be wide open. I think the 190 thermostat is keyed to prevent reverse installation.

If you're absolutely satisfied that the radiator is ok, the thermostat is open, and the pump is fine, then check your compression. Take another look at the fans.

If you want a project, replace the oil filter housing with one from a 60x turbo, along with the oil hoses and oil cooler. It should all bolt up.

I think you should verify that there is a problem with the oil temp before modifying engine components.

it may simply be your gauge that is misleading you. I think 1.5 bar is considered normal when warm. that does not give much room for inaccuracy the way you are reading it and from what you say.

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the engine will not over heat with the t-stat removed under typical conditions - from my experience. High, extended loads... different story.

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X2

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

If your Oil Filter Housing has a thermostat it could be the thermostat is ot opening.

Carefully check your Oil Cooler Hoses and see if they are getting hot.

Also I have had new Thermstats not open right out of the Box.

I used to test them before installing them because it is alot of mess and work to replace the new but defective one after it is installed.

Thermstats can also be installed backwards.

I suppose it is possible for a combustion gas leak from a leaking headgasket to create gas pocket that would keep the coolant from circulating and thereby the upper Hose does not get hot.
Try driving without the pressure cap on as that should allow the gas an escape route.

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84 300D, 82 Volvo 244Gl Diesel

I checked my spare, and verified that a 2.5 thermostat has an index detent which mates to a tab on the housing. It can only be installed the right way. It may be bad out of the box, but it's not going to be backwards.

Removing a thermostat on any car is pointless. Even if you get lucky and it doesn't overheat, it's not going to run any cooler. If you want to test the thermostat, put it in a pot of boiling water.

The engine is not going to overheat without a thermostat. Thats a myth.

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CENSORED due to not family friendly words

Get a cheap test kit and check for combustion gases in the coolant. You state you have a pretty hot engine and no heater output in comparison to what was at one time? This to me could mean a lack of normal circulation.

Did this cars heater work normally at any time during your ownership? You also should check to see if there is anyway to make sure the coolant has no air bubbles in the system. Some cars for example like the front ends elevated when putting new coolant in.