85 300d overheats - PeachParts Mercedes-Benz Forum

cnev300d · #1 10-24-2007, 05:45 PM

My car recently is having overheating problems.

Car was driven on freeway when the temp needle started climbing. Before this the temp showed normal or sometimes very low.

I noticed during the overheating that the hot air is not coming out of the vents. But at times when the hot air does come out, the temp needle returns to normal. I can also hear a wirling/grinding sound from the dash in front of the driver.

It seems like it's a clogged water hose? or some other device that's not working properly? Is it the mono-valve? Any insight is appreciated!

Car is a 1985 300d california edition. Thermostat changed a few months ago.

rrgrassi · #2 10-24-2007, 05:56 PM

Still check the T Stat. They are known to be bad out of the box. I need to replace mine again as well. When the weather gets cool like it has, the temp will go to 100 and stay during highway runs then drop at idle. During the summer, the engine temp stayed at 90. I have the 90 degree t-stat. I want an 80 degree fail safe.\

I'm thinking the t-stat is too sensative and is closing when the cooler water gets to it.

VegiBenz · #3 10-24-2007, 06:06 PM

I second the thermostat. I can't think of anything else that can cause an overheat condition so rapidly other than a water pump failing catastrophically which pretty much doesn't happen on our cars. I have seen many new thermostats bad out of the box as well.

patbob · #4 10-24-2007, 07:44 PM

Quote:

Originally Posted by rrgrassi

Still check the T Stat. They are known to be bad out of the box. I need to replace mine again as well. When the weather gets cool like it has, the temp will go to 100 and stay during highway runs then drop at idle. During the summer, the engine temp stayed at 90. I have the 90 degree t-stat. I want an 80 degree fail safe.\

I'm thinking the t-stat is too sensative and is closing when the cooler water gets to it.

Do you have an air bubble at the thermostat?

Could the cool airflow chill the thermostat housing enough to prevent it from warming enough to open until water is 100C?

A small hole drilled in the top of the thermostat might help with both of these problems.

carnut · #5 10-24-2007, 07:46 PM

First thought with gurgling noise is air in the cooling system. So check recovery cap, make sure it holds proper pressure. Pressure test system for any leaks. Test hot then with pressure tester on under pressure overnight to ck for leaks when only cold. From what you describe, the car is running hotter than normal not overheating. How high does the temp needle go? If no leaks found, and cap passes pressure test, then I would suspect thermal fan clutch.

cnev300d · #6 10-24-2007, 08:24 PM

Wow, thanks for all the quick responses. I have parked the car for now and am using my 87 300sdl.

A little more information and history:

When I first got the car 7+ months ago, the temp needle stayed at 0 degrees. So I changed out the thermostat; after which it started reading operating temp of around 80 degree C. I noticed that the old t-stat had a hole in it though and the new one didn't.

Anyways, the car runs along well all this time, but it did over heat once or twice before, but when that happened, I just added more coolant and it ran fine again. When it overheats, there is boil over...steam hissing from the engine area and I smell coolant in the passenger area. Needless to say I keep a good eye on the temp needle and top off the coolant all the time.

It feels to me that something is clogging the coolant to the engine and heater core? during the overheating episode since I turn on the heater and only cold air comes out. When hot air does blow out, the temp needle drops to normal right away. I'll try to do a flush and check out the hoses and such this weekend.

Quote:

Originally Posted by cnev300d

My car recently is having overheating problems.

Car was driven on freeway when the temp needle started climbing. Before this the temp showed normal or sometimes very low.

I noticed during the overheating that the hot air is not coming out of the vents. But at times when the hot air does come out, the temp needle returns to normal. I can also hear a wirling/grinding sound from the dash in front of the driver.

It seems like it's a clogged water hose? or some other device that's not working properly? Is it the mono-valve? Any insight is appreciated!

Car is a 1985 300d california edition. Thermostat changed a few months ago.

Jeremy5848 · #7 10-24-2007, 08:28 PM

Quote:

Originally Posted by cnev300d

...when the hot air does come out, the temp needle returns to normal...

This indicates that the system is almost working. Your statement says that extracting a little bit of heat from the coolant (with the passenger compartment heater core) makes the temp gauge happy. Unless the radiator core is partially clogged (internally or externally), the thermostat would indeed be the next thing to try. Without spending any money you could remove the thermostat and run the car without for a little while, see how hot it gets.

cnev300d · #8 10-24-2007, 08:38 PM

The reason I think something is clogging or malfunctioning is this:

I'd be driving along and everything is normal...heat blows out of the vents if I turn it on. Then bam, no heat out of the vents, cold air, and the temp needle rises.

If it doesn't climb too high, I fiddle around with the climate control and sometimes it'd kick in hot air again and when this happens, the needle immediately goes to normal. I also hear some whirling/grinding sound in the dash area right in front of me.

Then bam the needle rises again. This happens on either city streets or on the freeway. It only started happening when I was doing 80+ mph on the freeway and I normally only drive 60-70.

I do notice that the car runs hotter climbing hills and it does struggle up the hill. This is a turbo 300d.

patbob · #9 10-25-2007, 06:04 PM

Quote:

Originally Posted by cnev300d

When I first got the car 7+ months ago, the temp needle stayed at 0 degrees.

Highly unlikely this needle behavior has anything to do with the thermostat -- unless you really believe that the coolant is at 40C (my gauge only goes down to 40C, so I assume you meant that rather than actually 0C).

Quote:

It feels to me that something is clogging the coolant to the engine and heater core? during the overheating episode since I turn on the heater and only cold air comes out. When hot air does blow out, the temp needle drops to normal right away. I'll try to do a flush and check out the hoses and such this weekend.

This can happen when there's a slug of cold coolant in the heater core. It's hard to get it to happen more than once in a driving session, or even in a day for that matter, so if you're seeing it repeat, then this probably isn't what's going on.

Stevo · #10 10-25-2007, 08:27 PM

I'm guessing you have air in the system from changing the T stat. How did you bleed the system when you did the T stat?

cnev300d · #11 11-07-2007, 01:18 PM

Woo! I got the 300d running again. Here's what I did:

Flush out the old coolant. I didn't use any special flushing kit. I disconnected the coolant line to the engine and the heater, hooked up a water hose, open the radiator drain and let the water flow through. The water coming out was quite murky. I also ran water through just the radiator to flush out any gunk.

I also removed and cleaned the reservoir and replaced the thermostat. Then I ran the car on just the water for awhile. It never overheated and the heater blew hot.

After this I did the same flushing, blew out as much water as I could with air and fill with a mix of 50/50 coolant and distilled water.

I ran around for about 10-15 minutes and still no overheating. I ran 30 miles/35 mins to work today and it only went up to about 60 degrees.

In the process of flushing out the coolant and messing around with flushing the radiator I managed to break the plastic hose connector to reservoir off the radiator. I noticed after removing more of the plastic that there's a threated metal part on it. Went to the hardware store and found a screw with a hole in it and threated it back to the metal part and it seems to hold nice and tight! Saved me from having to replace the radiator. yay!

cnev300d · #12 11-13-2007, 07:43 PM

Crap. Still got the same overheating problem.

Temp still climbs when hot air is not blowing out of climate control.

When hot air does blow out, temp is normal.

I can hear this grinding sound from the dash as if something is opening when the hot air does finally blow out.

What's behind the dash (right in front of driver)? Is it the heater core plugging up? I can see coolant hoses going from the engine into the cabin. Looks like it's pretty hard to get to the heater core? under the dash.

Can I prevent this overheating by completely removing the t-stat or drilling a couple of holes in the t-stat?

winmutt · #13 11-13-2007, 08:43 PM

Quote:

Originally Posted by cnev300d

Crap. Still got the same overheating problem.

Temp still climbs when hot air is not blowing out of climate control.

When hot air does blow out, temp is normal.

I can hear this grinding sound from the dash as if something is opening when the hot air does finally blow out.

What's behind the dash (right in front of driver)? Is it the heater core plugging up? I can see coolant hoses going from the engine into the cabin. Looks like it's pretty hard to get to the heater core? under the dash.

Can I prevent this overheating by completely removing the t-stat or drilling a couple of holes in the t-stat?

Did you try replacing the thermo stat yet? Grinding is probably not so good. This is your aux pump. I suggest finding one at the yard on the cheap.