I was able to locate my thermostat housing and remove the hose, but there is no obvious way to remove the thermostat, other than prying it out. Before I do something stupid, and expensive, could someone tell me how to remove this device, and then how to determin if it works?

Recently, my engine has been running too cold, and this could be the suspect.

Eric

Cover the top of the thermostat with a rag and tap it lightly with any rubber coated screwdriver handle. It should come loose. At normal ambient temp, it should be closed, you should not be able to see any daylight around the thermal element and the outer ring. If you do, toss it a get a new one. If you don't, toss it and get a new one. They are inexpensive, good insurance and anyway, who wants to mess around with thermostat testing. If the part is doubtful, replace it. Peace of mind, confidence and a happy engine will surely follow..

Thanks Jeff.

It's in a saucepan boiling right now, and looks like it has opened about 3/8 inch. Doesn't seem like much, considering there is more room to go -- but that is a pretty big resistance spring.

It did not open until it started to reach a rolling boil -- but then 87 dgrees C is 188.6 degress F -- just 24 degrees shy of boiling anyway.

Also, I heard a rattle -- like a small ball bearing inside -- when I shook it. Is that normal?

Nonetheless, I'll replace the part since it is so easy and cheap, and see what happens.

Eric

Should be fully open at 87-88F. But wait...you said your's was running too cold!! so..it should be opening real early or stuck open. The little ball is a check valve to equalize pressure between the block and radiator. Toss it and get a new one. Boil some eggs instead..:)

That sounds fairly normal for an M103. A lot depends on the ambient temp, especially at idle. Sounds like cool running is no longer an issue..

Jeff,

Seems to be working -- after a long while. The temperature dips just a bit below 80 at 70mph+ but that may be a temporary condition. After idling for a while, it got hot enough for the aux. fan to kick in, but then cooled back down to about 100-105.

Eric

Cool running is no longer an issue at idle, or when the outside temperature is above 75 or so degrees.

I still run at exactly 80, or can dip just a hair below, when the outside temperature is below 75-80. But in the summer, I am not worried about that.

The amazing thing is how I am able to achieve my higher temperatures, which I will describe in a new thread called "Spark Gap Myths/Facts" since it is a bit off-topic here.

Eric

A Big Star
 

Brothers of The benz, All
I recieved my latest edition of The MBCA Star Magazine.
It has one of the best Technical Articles I've read.
Subject: Cooling.
You must read this to answer all of your questions.
IT'S SUPER!
Happy Trails Beep Beep from The Spiderman in Houston!!!

Interesting Eric, as I am playing around with my cooling system now as well. It's hell hot here in Texas, and on one of those 102-degree days, I noticed my temp gauge hitting 105 while idling for a long time at the house. My aux fans are working properly, and maybe I'm just a little too anal, but I am used to seeing the gauge read about 85 or so when idling.

Temp is just below 85 when driving around town and on the highway, but it gets to just over 85 when I am stuck at a long light. In a hot afternoon, it creeps up to 100 at a long idle, and then over that if I am idling for more than 10 minutes. I don't remember what is normal for these cars, but I want to be safe than sorry.

I decided to do the boil test, and too, found that the thermostat was snug. I believe this is due to the fact that the system is pressurized, and there is a bit of a vacuum to contend with when removing it. I gently pried around the thermostat with a flat tipped screwdriver until I heard the seal release the pressure. Then it came out easily.

It opened up when the water came to a boil, but I don't know what is considered normal. I put the thermostat back on since I had to go to work a few hours later, but I guess for the price, I might as well replace it. My service receipt for the new water pump install made no mention of replacing the thermostat as well, so I guess it's about due. Make sure you top off with additional coolant, as you will lose several ounces of coolant mixture after removing the part...

[Edited by G-Benz on 07-17-2001 at 01:52 AM]