1987 300TD keeps Over Heating : ( Need advice before I drop off at shop - Page 4 - PeachParts Mercedes-Benz Forum

Targa-NF · #46 04-23-2010, 07:56 PM

Just found a 72 VW Bug on Cragislist #%$& IT !!! I'm going air cooled....
Thanks everyone for today. I will be back at it tomorrow. Going to have a few drinks and try and wrap my head around whats going on... Thanks Again.
Jason

TnBob · #47 04-23-2010, 07:58 PM

Ok so you have good static flow that is confirmed.
Radiator is good.

That only leaves the thermostat and the water pump.

Id snug it back together without the thermostat and see if
you now have good flow. If you do, your current thermostat
is highly suspect.

If you dont, its water pump time.

JimSmith · #48 04-23-2010, 08:00 PM

There should already be a little hole, and the little hole goes on the high side of the thermostat as it sits in the housing. If there is no hole, you may have the wrong item.

Given the radiator was described as stone cold with the engine running it seemed to me the fan operation was not part of the problem. Checking the hose from the engine to the radiator to see if it is hot close to the engine and then not so hot close to the radiator might confirm the problem is no flow through the hose to the radiator. In the old days you could open the radiator cap and look for flow in the radiator.

Jim

Targa-NF · #49 04-23-2010, 08:03 PM

Pump looks good. No slippage on the impellar and looks to be good shape . Can it look good but work bad?

Targa-NF · #50 04-23-2010, 08:12 PM

When she hits 110-115 the upper rad hose is hot and so is the rad for about a inch around where the hose goes in. Rad and lower hose are cool.

And I got t-stat in my hand. No hole. Should I put one or two in? I know that you cant take out the t-stat all together. But will a few holes hurt? Also when she get up in the 115, range I pull over and let her idel with the heat on bust. she will go down to just under 100

Targa-NF · #51 04-23-2010, 08:17 PM

Have not confirmed flow from top rad hose. Going to put her back together and fill with water and start pulling hoses

Will see what happens. I hope I get wet...

JimSmith · #52 04-23-2010, 08:52 PM

I admire your persistence. There is nothing wrong with your pump, put it back in. I hope you have a new gasket or O-ring for it to seal it to the block.

Did you boil the thermostat yet? These things are more complicated than most and they are manufactured by the same organizations that make more conventional ones, where price per unit seems to be a higher priority than whether or not they work. Check the archives, there have been several cases of thermostats being useless out of the box, taken back to the store and replaced with another, even from an MB dealer, and the second unit is bad. A new thermostat is not "good" unless you verify it is "good." Boiling the old unit and the new unit will tell you. One flow path opens and the other closes. Make sure you install the item correctly as well. Upside down is not going to work, at all.

No thermostat might be of some benefit in cooler weather. In hot weather "no thermostat" does not force all the flow from the water pump into the radiator.

I asked earlier if your problem is at idle, while driving over the road (highway speeds) or both. This is vital to know since the car moving pushes air through the radiator to the point where there is little need for the fan to do anything - thus a clutch on the fan. One kind is viscous, another is electromagnetic. The whole point of a clutch on the fan is to avoid the losses of powering the fan when the engine is not too warm, and to limit the losses when the engine is warm by limiting the fan drive speed. Electromagnetic ones are "binary" - they are on or off and they don't like to turn on when the rpms are high (lots of stress on the clutch). Originally they were popular in Europe since most non-air conditioning equipped cars (most cars up to the 1990's over there) don't have a need for the fan when the engine is running at high speed since the car is moving fast enough cause sufficient air to go through the radiator to cool the engine. With the advent of universally installed air conditioning, this concept became less attractive - in hot weather the a/c heat load dumped in front of the radiator required a fan to run at least at some minimal speed to get the flow needed cool the engine sufficiently too. A viscous clutch seemed to be the answer.

The viscous clutch is designed to some torque transmission characteristic that is triggered by the temperature of the air coming through the radiator. So, if that air is too hot, the viscous clutch "turns on" and has specifically limited torque transmission characteristics (once you get to a certain rpm the torque to drive the fan faster as the engine speed increases exceeds the viscous clutch ability to transmit torque and the fan speed levels off as engine speed increases) to avoid overspeeding the fan, limiting the fan load on the engine (better mpg) and to avoid noise. I don't know if your car has a viscous clutch or not, but they came into production in the mid to late 1980's.

If your engine temperature drops from 115C to normal (~80C) when you get on the highway, the problem is not with the water circulation system - it is the fan clutch, which ever one you have.

If it is a viscous clutch it has a larger diameter finned aluminum housing, and you test it by running the engine to that temperature - 110C - shut the engine off just after someone pops the hood and then looks at the fan. If it freewheels for any length of time the clutch is bad. At that temperature the viscous clutch should be pretty stiff. With the engine stopped you can try turning the fan by hand - you should feel some substantial resistance. No clutch action means the fluid leaked out. For you it means either buying a new clutch (another big bill) or mechanically over riding the clutch mechanism - a permanent "fix" that is accomplished by driving a screw in the axial direction into a strategic location in the hub. I believe you can find a thread with this info in the archives. Works fine, but wears the bearings out and there is a theoretical chance of a fan blade becoming detached with the engine running up to redline. Remember though, the thermostat first since the viscous clutch will not activate if the thermostat is bad, and when the fan hub is not heated by heat from the radiator the clutch does not engage.

So, check the thermostat in boiling water on a stove. React accordingly (buy a new one, boil it, etc.). Check the viscous clutch if that doesn't work.

Jim

JimSmith · #53 04-23-2010, 09:02 PM

Quote:

Originally Posted by Targa-NF

When she hits 110-115 the upper rad hose is hot and so is the rad for about a inch around where the hose goes in. Rad and lower hose are cool.

And I got t-stat in my hand. No hole. Should I put one or two in? I know that you cant take out the t-stat all together. But will a few holes hurt? Also when she get up in the 115, range I pull over and let her idel with the heat on bust. she will go down to just under 100

Go ahead and drill a 1/8" hole in the outer rim, inside of the gasket seating area - meaning at a smaller diameter, no on the gasket seating surface, after you boil the thing to see if it is working. Check the brass bushings and see if they are shiny on one side or for any other signs of binding.

Jim

Targa-NF · #54 04-23-2010, 09:29 PM

Thanks Jim. Everyone has been super helpful. I put myself in a bad place by buying a car and hoping it would run right. I have had my shear of SD's and CD's They have never let me down. Never had a problem that was to hard to fix. I know this was going to be a different beast all together, but was not ready for this. The wife asked me before I left to pick this car up in VT, that I would not have a problem picking her and the kids up in Halifax NS and we all driving home to Newfoundland together. I told her not to worry... Its a Benz Diesel. They will get you to hell and back without a hitch... So I jinked myself and here I am. A week late and counting... Just hope I can find the problem. I would hate to have and leave her here. Will never hear the end of it from the wife, She will stop trusting my SD and not complain about the cash for months. I am going to boil my T-Stat after dinner. Hope its broken. Then I will have a answer. But like everything else on this car Im sure it fine.
I only over heat when driving. Its worse when I'm on the highway. Can drive in town a bit and she get hot but not " Too Hot " but when I get on the highway she rockets to the red.... I stop and let her cool for a min then go again for 2-3 min before I have to stop again. Thanks again.
Hope tomorrow is a little better.

jonbobshinigin · #55 04-23-2010, 10:37 PM

Fans do not seem to be an issue because the radiator never gets hot. Keep that in mind. Putting it back together and running without a thermostat should take a thermostat issue out of the equation. Stick with it so long as it doesn't cause issues with your family. But really, they are great cars. Cooling issues need to addressed initially on these cars otherwise you will begin to risk the original number 14 head.

polarisrmk · #56 04-24-2010, 12:28 AM

could you be putting the thermostat in backwards? I know this sounds dumb but i think it is possible if i recall... It wouldn't open if the correct side of the thermostat didn't get hot... just thinking outloud

Targa-NF · #57 04-24-2010, 08:19 AM

Was lying in bed last night and thinking about how cooling system works. So i got a few pics and lets see if I'm right. Because If I am that would explain everything.

First pic is how I found it when I open it the first time. It will only fit in that way because of a little notch that wont let it.

Second and third pic is of notch. Thought it was there so you could not put in backwards.

Forth pic is of how I thought it should go in from the beginning. Because I thought that the second action on the T-Stat " the part on the top " was to redirect the coolant flow. But it dont fit in right because of notch.

I am going to grind away the little notch and try it. Got a good feeling....

Junkman · #58 04-24-2010, 09:07 AM

The side of the thermostat showing in pic 1 goes toward the radiator.
The side showing in pic 4 goes toward the engine.

layback40 · #59 04-24-2010, 09:07 AM

Well we can see you got the thermostat out.

Have you put in hot water yet?

Dont worry about trying to reverse it, its the right way in your pic 4.

Go and put it in the kettle. If it doesnt open right up well before it boils it no good. You can do that if you dont have a thermometer. Your problem is so bad that as long as it opens well before the water boils it would be unlikely to be the cause.

Is the opening temperature stamped on it?

Targa-NF · #60 04-24-2010, 12:19 PM

In pic one was the only way to put it in. I had to remove the little notch in pic 2 and 3 to get it in like pic 4. I put it in like pic 4 after removing little notch and she still over heats.

Here are some pics of where I have my aftermarket temp sensor put. It reads 190-210 on back roads. lower rad hose still cool.