W124 300D Getting Hot - PeachParts Mercedes-Benz Forum

DieselPaul · #1 12-12-2012, 05:27 PM

So,

On Sunday in traffic I noticed my 300D would get a little above 100* and it was like 40* outside. I also noticed that the heat was cold.

The temp would climb then drop down to near where it should be and the heat would get hot.

Then it would get warm again, but as long as you were moving the temp would stay safe.

I drove it 120 miles on home and the temp stayed just above the 80* mark where it usually is.

I ordered a thermostat from the dealer on Monday, it came in today but I wasn't able to go get it.

However in the interim few days the car has not acted up. Until today headed to pick up a truck it was doing it again but hotter than before. As I was pulling into my friends neighborhood it was sitting solid at just shy of 120* and the heat was blowing ice cold on the defrost setting. So I shut her down, picked up the F250 and left the 300D at my friends house.

The coolant level is where it needs to be, and it is fairly fresh OEM coolant. I change my coolant about every year. And I replaced the lower radiator hose last year.

The water pump weep hole is dry.

No obvious leaks. And its not smoking or idling rough, so don't suspect my #14.

Could this just be the thermostat? As far as I know it is original. I would think it sticking closed would make the heat cold because flow through the heater core would be limited.

And don't worry I'm not going to limp it home. I picked the truck up to tow my trailer to get a 190E tomorrow, so I will go back tonight with the trailer to get the 300D. I'm not trying to do a thermostat AND a headgasket.

vstech · #2 12-12-2012, 07:26 PM

check with an infrared thermometer... it could be a bad gauge, or a bad temp sender, or a bad ground to the block... all will indicate high temps...

the lack of heat makes me think, bad pump bad aux pump, bad coolant level...

Brian Carlton · #3 12-12-2012, 07:54 PM

Quote:

Originally Posted by vstech

the lack of heat makes me think, bad pump bad aux pump, bad coolant level...

The combination of elevated head coolant temperatures coupled with no heat clearly leads to a conclusion of low coolant.

Remove the upper radiator hose and pour coolant into the hose until the head is completely full of coolant. Do this with the vehicle elevated at the nose by at least one foot.

DieselPaul · #4 12-12-2012, 09:33 PM

Quote:

Originally Posted by vstech

check with an infrared thermometer... it could be a bad gauge, or a bad temp sender, or a bad ground to the block... all will indicate high temps...

the lack of heat makes me think, bad pump bad aux pump, bad coolant level...

My aux pump has been bad for years I think. My heat is always warmer when moving, and it cools off at stop lights. I check it for leaks occasionally but it never bothered me. How would a bad aux pump make my car overheat.

I think the gauge is fine considering the way in which it moves seems accurate. It doesn't just like peg hot, it works it way up and as you move it'll cool off.

I'm going to try Brians bleeding method, and I think I am going to throw the thermostat at it anyway. It was $20 from the dealer.

I towed it home, I'll mess with it Friday. I'll be out of town getting the 190E tomorrow.

Brian Carlton · #5 12-12-2012, 09:36 PM

Quote:

Originally Posted by DieselPaul

I'm going to try Brians bleeding method, and I think I am going to throw the thermostat at it anyway. It was $20 from the dealer.

Fill the head first. Then drive it.

Why do any work if you don't have to.............??

rscurtis · #6 12-13-2012, 10:50 AM

Don't rule out the possibility of a combustion leak that is displacing the water in the heater core or water pump.

DieselPaul · #7 12-13-2012, 10:09 PM

The car runs too good for a blowing headgasket.

The expansion tank is "full" when the motor is cold.

No oil in coolant, no coolant in oil. No white smoke, no grey smoke. Starts fast on all 6. Smooth idle. It's not a headgasket.

DieselPaul · #8 12-13-2012, 10:10 PM

Quote:

Originally Posted by Brian Carlton

Fill the head first. Then drive it.

Why do any work if you don't have to.............??

Deal. I've got my trailer out so I figured driving up the ramps
Would give me plenty of angle to elevate the nose.

barry12345 · #9 12-14-2012, 12:43 AM

No heat at operational temperatures or above does not usually mean thermostat. It instead indicates either very low coolant as suggested or very poor circulation.

Since it seems somewhat intermittent the water pump is probably okay. You do have a well tensioned belt? Do an exhaust gas test of the coolant as unfortunatly it could also be a head gasket. Thats if the coolant is really full.

There is a bypass around the thermostat to enable circulation of the coolant inside the engine and heater until the engine gets hot enough to open the thermostat normally.

Although I have not dealt with this issue on older mercedes diesels. I have seen it on other brands. Your list of suspects to me does not include the thermostat. Water pump or head gasket are higher on the list in my opinion. Hope I am wrong though. Time will tell.

DieselPaul · #10 12-14-2012, 09:29 AM

My belt is squeaky, the tensioner shock is new but the spring is original. The tensioner arm is also new. The Pulley is new too. All dealership parts. The spring felt extemely strong but thats far from a precise measurement. If the new belt makes noise i will order a Spring. I've got a new belt on the shelf it needs to be done anyways to fix the chirping.

Ill attack this car tonight, my evening is open.

barry12345 · #11 12-14-2012, 10:11 AM

Water pump to me does not seem to require a large amount of belt pressure like an alternator does. So unless it seems pretty obvious the belt is loose it should not be the issue. On the otherhand you state the belt is squeeky. you can take a bar of face soap and drag it along the belt with the engine off for safety. This will increase belt traction for an hour or so normally. That is a simple expediant I have used many times when away from home with no tools to tighten a belt in the old days. It is more than safe to say I originated in the v belt days.

If the belt also serices the alternator and it is not continiously squeeling then it is not it in my opinion. If the test kit for byproducts of combustion in the coolant is say ten bucks I would consider getting it. That is after I was certain the coolant is really full. The important clue here to me is how the heater is responding during the issue. Stil as I mentioned before I have not had to address a problem like this on mercedes products.

It is not always belt tension that determines belt traction. Sometimes they glaze the friction surface quite bad this really impacting their traction. Since it is the #14 head you might want to see if your coolant hose remains hard in the morning.

Zulfiqar · #12 12-14-2012, 10:16 AM

The belt length can also be an issue, I have my original owners manual for the car and it says to use a 2145mm belt which I did - gatorback belt.

I have come to know that some cars had a 5mm shorter belt.

Check the pressure cap, if it fails to hold pressure the water in the coolant can boil.

DieselPaul · #13 12-14-2012, 04:38 PM

Thermostat seal was cracked and rock hard, minor leak.

The auxiliary pump was leaking where the two halves are held together by screws pretty well. It was on the very bottom and the belly pan was making the leak look like it was coming from further forward in the car.

Put a new belt on, new thermostat and seal, and replaced the auxiliary pump. Bled it with Brians method, I've got hot heat, and my temp is rock solid at 80*C. I've got drive to a friends about a half hour away tonight, we will see how she performs.

Hopefully those were my only two leaks.

barry12345 · #14 12-15-2012, 10:54 AM

Glad to hear it was low coolant because of leaks. All too often the issues turn to the number fourteen heads on these engines.

Because of the sensitivity to overheating of this head. I would keep the cooling system hoses changed out at reasonable intervals. If you had found your coolant full unfortunatly the bubble formed in the coolant blocking flow to the heater core may have been a real possibility.

I still feel that a percentage of head issues on these engines are aided by owners not allowing the internal casting temperatures to equalise a little before shutting down the engine.

Especially right after coming off the highway say to a fuel pump. There is no time for hot spots to equalise slowly. Even just letting the engine idle for a minute is perhaps good insurance before shutting down. It certainly will not hurt anything if you think about it even if it does not help.

DieselPaul · #15 12-15-2012, 12:04 PM

I always let my motor idle for several minutes after a highway run. I hadn't considered equalizing the casting temps, my intentional was to circulate and cool the oil to lengthen the turbos life.

I'm also the guy that got yelled at in another thread for suggesting replacing hoses as preventative maintenance.

I'm also the guy that changes his coolant annually.

I take caring for this car very seriously.