97 E300D No Heat - PeachParts Mercedes-Benz Forum

godowning · #1 11-18-2022, 03:42 PM

Good Afternoon, I have done a bunch of reading and testing, but haven’t found a solution to my no heat problem.

A little background first. I have owned the car for a couple of years. Has always had a no or sometimes low heat issue. The car spent 95% of its life in Florida.

As part of some ongoing maintenance and in trying to resolve the no heat issue I have done the following. I replaced the thermostat and the car consistently runs right around 85 degrees. Replaced the coolant with the proper Zerex formula after the thermostat replacement. Replaced the duo valve with a brand new Mercedes part. For a little while the heat worked after the car was up to temp, but only if the fan was on the lowest setting. Anything higher and the temp would get cold. For the last few weeks I have had no heat at all.

I have also unplugged the electrical connection to the duo valve as I read that should result in heat all of the time. Still no heat.

What should I look at next? Driving me crazy as this is my snow car with heated seats and snow tires. It’s in the 20’s today and snowing in the mountains of WV.

Thanks in advance.

jsb357 · #2 11-18-2022, 05:14 PM

Quote:

Originally Posted by godowning

I have also unplugged the electrical connection to the duo valve as I read that should result in heat all of the time. Still no heat.

^^^^ Can someone verify that statement.

pimpernell · #3 11-19-2022, 07:17 AM

Quote:

Originally Posted by godowning

Good Afternoon, I have done a bunch of reading and testing, but haven’t found a solution to my no heat problem.

A little background first. I have owned the car for a couple of years. Has always had a no or sometimes low heat issue. The car spent 95% of its life in Florida.

As part of some ongoing maintenance and in trying to resolve the no heat issue I have done the following. I replaced the thermostat and the car consistently runs right around 85 degrees. Replaced the coolant with the proper Zerex formula after the thermostat replacement. Replaced the duo valve with a brand new Mercedes part. For a little while the heat worked after the car was up to temp, but only if the fan was on the lowest setting. Anything higher and the temp would get cold. For the last few weeks I have had no heat at all.

I have also unplugged the electrical connection to the duo valve as I read that should result in heat all of the time. Still no heat.

What should I look at next? Driving me crazy as this is my snow car with heated seats and snow tires. It’s in the 20’s today and snowing in the mountains of WV.

Thanks in advance.

Do I need to burp my cooling system?

You'll need to burp or bleed the cooling system to remove any air. When you fill up the coolant system, the radiator may fill up entirely, but the engine may not fill up all the way, leaving air in the system. Air pockets can prevent coolant from circulating and can cause problems like the thermostat not opening.

godowning · #4 11-19-2022, 07:36 AM

I have tried burping my coolant system numerous times by leaving the expansion cap off for a few days and even driving without the cap.

Murkybenz · #5 11-19-2022, 08:10 AM

Find the duo valve and loosen the hose connection that is the highest .. then wriggle the hose so it’s loose but do not pull it off as it’s awkward to get back on.. get a very thin screwdriver and stick it under the hose so you can lift it slightly and let the air burp out.

nelbur · #6 11-19-2022, 04:36 PM

Your engine has a coolant bleed bolt about two to three inches behind where the radiator hose goes into the head. There is a large hex head bolt with the head facing up. You typically open the bolt part way and fill the coolant into the bottle until it starts to come out the bleed bolt. Then it can be tightened and the air should be gone.