1987 300TD keeps Over Heating : ( Need advice before I drop off at shop - PeachParts Mercedes-Benz Forum

Targa-NF · #1 04-22-2010, 01:40 PM

Hi everyone, I did a search and could find a few answers, but need advice.
My 1987 300TD 168k Miles keeps over heating. By over heating I mean always up around the 110-115 mark. I have the heat on bust at all times and am driving on normal roads. I replaced T-stat and replaced coolant. Checked all hoses, and filled coolant on a hill to get as much air out as I could. I am not getting any flow through the rad I think. The cars temp will be at 110-115 and rad is stone cold. Upper rad hose is hot lower is cool. The shop said its most likely the rad. The pump is not leaking at all. What do you all think? The rad is going to cost me 350... : ( Then the cost to install. If that don't work I'm guessing the pump is the next to replace. Is there any way to test it?
Thanks.
Jason

TnBob · #2 04-22-2010, 04:17 PM

If your system is air free, how about pulling the radiator and taking it to a radiator shop? Just might need a professional flushing.

Typically that a $30/40 job.

BrianCostello · #3 04-22-2010, 05:41 PM

X2 on raditor flush

also is your "fan clutch" working properly?

do a search for it. . I bet that it needs replacing

Targa-NF · #4 04-22-2010, 06:30 PM

What would she be doing if the head gasket was gone? I dont have a coolant smell or oil in my coolant.

Aquaticedge · #5 04-22-2010, 07:00 PM

likely not. you'd notice a coolant drop and or Diesel or oil mixing in your bottle as well. there'd be several obvious signs

johnathan1 · #6 04-22-2010, 07:23 PM

Is the coolant level full?? If the ENTIRE radiator is stone cold, then I would think water pump. If the radiator just has cold spots, then it probably needs to be flushed (doesn't always work) or replaced.

JimSmith · #7 04-22-2010, 08:07 PM

It would be good to know if your problem happens at idle only, idle and over the road, or just over the road.

Generally, if the radiator is cold, the fan clutch and other external stuff is not the problem. Typically the radiator is cold when the flow rate to the radiator is too low compared to how well the radiator can dump heat into the atmosphere. This can be for several reasons. One, the pump is shot. This would likely lead to severe overheating over the road and even at idle - nothing to make it stop at 115 degrees C.

Next, it can be a problem with the thermostat. Even a new one. Several here have reported in the past that they have changed thermostats, found the new one to be malfunctioning, and then experienced the same result the second time. Test the thermostat. These thermostats are double acting - they mix cold radiator water with warm or hot water from the engine to avoid thermally shocking the engine as it heats up, and then to regulate the engine temperature without causing a lot of thermal stress (such as would be the case if the water from the radiator was, say, -20C and the engine outlet to the radiator was, say, 110C. As the load continues to increase the two parts of the thermostat cooperate to close off the bypass line and force all of the water from the engine side into the radiator - a condition expected only when under severe load and the ambient air temperature is very high - in order to keep the coolant temperature stable.

Until this sequence of events under high load happens, it is possible that a cold feeling radiator is just the result of the radiator being able to remove the very little heat from the minor flow of hot water from the engine before the radiator heats up. However, with the engine at temperature (110 to 115 degrees C for you) there should be nearly full flow through the radiator, and for the flow to be choked to the point where the radiator is cold there has to be either a thermostat problem or another flow restriction.

At this point I would take the thermostat out (note exactly how it was installed - if it was in backwards it will not work right) and boil it in a pot on the stove with thermometer in the water and look to see when it begins to open and when it is fully open (temperature wise). Should start to open before or at 80C and be fully open at boiling if you are at sea level. Fully open is a peculiar bit of motion. One side opens the other closes. Don't have the manual here, but some of these guys do and can scan the diagram. The bypass line closes and the path to the radiator fully opens. And they begin to move at different temperatures, if I recall correctly.

If the thermostat is ok, the radiator is likely plugged. A flush, and if that does not work, a new one.

Someone has mentioned trapped air. I fill my W123s, W124, W201 and W210 by driving them up a sharp incline in the yard and with the nose well above the rest of the coolant containing parts, I fill it up, run the car, fill it up, run the car all with the heat on full blast. Air can get trapped and, being compressible, can block flow by occupying the flow area and not be able to be flushed away by the output of the water pump. This usually causes erratic temperatures though, not just high ones.

Good luck, these high temperature things can be mysterious at times.

Jim

vstech · #8 04-22-2010, 08:45 PM

my bet is bad thermostat, and a slightly dirty radiator. dirty on the inside that is. think about it. cold lower hose means the radiator is cooling the coolant that is flowing through it.

jt20 · #9 04-22-2010, 08:56 PM

replace the pressure cap before you pay anyone to do anything.

Targa-NF · #10 04-23-2010, 11:58 AM

I just spent 540 on new rad and still have problem. But now when she gets hot i loose my heat. i pull over and give her a good reving and the heat comes back and she cools down a little bit. Going to loose my mind and my wife if I dont get this thing working right and head back to Canada....

JimSmith · #11 04-23-2010, 12:38 PM

Quote:

Originally Posted by Targa-NF

I just spent 540 on new rad and still have problem. But now when she gets hot i loose my heat. i pull over and give her a good reving and the heat comes back and she cools down a little bit. Going to loose my mind and my wife if I dont get this thing working right and head back to Canada....

I believe these cars have an auxiliary pump to ensure flow through the heater core when the engine is at low rpm, since the main water pump does not produce the necessary pressure at low engine speeds to drive fluid through the heater core. Sounds like yours is shot, or you had air in that section of the system from the radiator exchange. There are lots of threads on the subject and a variety of fixes besides just replacing the unit, if you determine it is bad. And, take the time to get the air out of the system.

As for the radiator, well, the only moving part of concern is the thermostat in this system, other than the water pump. The thermostat is a complicated by comparison to many others, and it is cheap. They are unreliable new. Take yours out and boil it in a pan on the stove with a thermometer and watch what happens at what temperatures. You only do the expensive things when you have data to show they are necessary. A thermostat is cheap by comparison, and a hell of a lot easier to get in and out.

Jim

Targa-NF · #12 04-23-2010, 02:09 PM

I saw in a post that its ok too drill a few small holes in the t-stat too let a little water through. Is this right? I am still going to take out the t-stat and test it, but would like to know if I should do that while its out.

jonbobshinigin · #13 04-23-2010, 02:39 PM

Quit throwing parts at it...unless you know they are old and you can afford it.

You need to check to see if you Main fan it engaging. I forget the exact temperature but it is before 100. 100 is the next line above 80. At 105 the electric fans in front of radiator should turn on, please test that and let us know. I have dealt with this on my 1987 300TD, I can probably help!

polarisrmk · #14 04-23-2010, 02:43 PM

Quote:

Originally Posted by Targa-NF

I just spent 540 on new rad and still have problem. But now when she gets hot i loose my heat. i pull over and give her a good reving and the heat comes back and she cools down a little bit. Going to loose my mind and my wife if I dont get this thing working right and head back to Canada....

$540

I replaced my radiator for $170 Shipped to my house. Behr OEM radiator was a 20 min job! Some of these mechanics are out of their minds!

Have you checked the Impeller on the water pump? could it be possible that you have lost "fins" on it? This happens all the time on VW's and Audi's but they are plastic blades.... just sounds to me like you have no circulation or very little from your pump.

Targa-NF · #15 04-23-2010, 02:57 PM

The rad is not getting hot. Upper hose is mad hot, rad and lower hose is cool. still spitting out a little coolant from the overflow when she get above 110-115c. I put on a new coolant res cap as well. Elect fan up front is wired to stay on all the time. IE switch on the dash. How do I know if the main fan is engaging? It spins as fast as the pump pulley. I really want to thank everyone for helping. I am at the end of my rope.... Got the wife with my new born waiting at her sisters for me in Halifax to bring them back to Newfoundland. I'm a week late so far and she ready to leave me if I'm much longer.
Thanks again.
Jason