Replaced Mono Valve Internals – Still no heat at speed. - Page 3 - PeachParts Mercedes-Benz Forum

whunter · #31 01-21-2014, 03:21 PM

Quote:

Originally Posted by funola

An easy way to check if there is air in the heater core or other problems is after a high speed drive with heat on, pull over and feel all the hoses going in and out of the fire wall. If they are cold, there is air or blockage.

Correct.
You forgot to mention:

If the radio is off, you can may hear a gurgle = a sure sign of air in the system..

.

funola · #32 11-15-2014, 10:34 AM

Originally Posted by funola View Post
There is a copper mesh between the 2 rubbers. Do you know what it's supposed to do?

Quote:

Originally Posted by tangofox007

I have not figured that one out.

It's been a while but have you figured it out yet?

steamboatsykes · #33 11-15-2014, 01:07 PM

Just an update on the thread, original issue was a torn original monovalve seal. Went through two MTC repair kits with no result.

Found a new Bosch kit (in box) on ebay and it solved the heat at speed issue. Stay away from the MTC kits. One thing I noticed about the Bosch unit is that it had a lot more clearance going into the coil. Both MTC's were a very tight fit.

Always thought the screen was a flow passage.

Gregory · #34 11-26-2014, 05:44 AM

My heater gurgles. Several have posted that air in the heater core can prevent cabin heating.

So far, nobody has posted on how to get the air out of the heater core.

I pulled the magnet & guts out of a monovalve from a P&P yesterday for $5. I forgot to take the spring. Before I replace my existing, I guess I should try to get the air out of the heater core.

funola · #35 11-26-2014, 09:06 AM

Quote:

Originally Posted by Gregory

My heater gurgles. Several have posted that air in the heater core can prevent cabin heating.

So far, nobody has posted on how to get the air out of the heater core.

I pulled the magnet & guts out of a monovalve from a P&P yesterday for $5. I forgot to take the spring. Before I replace my existing, I guess I should try to get the air out of the heater core.

Why didn't you just take the whole monovalve and take it apart at home?

If you have a healthy cooling system and engine, air in the heater core should purge itself just from driving with the heat on. The current flow created by the water pump should push the air pockets out of the heater core up to the expansion tank (highest point) and out the pressurized cap.

funola · #36 11-26-2014, 09:10 AM

Quote:

Originally Posted by steamboatsykes

Just an update on the thread, original issue was a torn original monovalve seal. Went through two MTC repair kits with no result.

Found a new Bosch kit (in box) on ebay and it solved the heat at speed issue. Stay away from the MTC kits. One thing I noticed about the Bosch unit is that it had a lot more clearance going into the coil. Both MTC's were a very tight fit.

Always thought the screen was a flow passage.

Was the MTC fit so tight that it hindered solenoid travel/ movement?

If you cut away the screen, you'll see the coolant has no place to go behind the screen, it can only go in then out the screen, which begs the question: what does it do?

Gregory · #37 11-26-2014, 10:10 AM

Quote:

Originally Posted by funola

Why didn't you just take the whole monovalve and take it apart at home?

If you have a healthy cooling system and engine, air in the heater core should purge itself just from driving with the heat on. The current flow created by the water pump should push the air pockets out of the heater core up to the expansion tank (highest point) and out the pressurized cap.

I could not get to all the hose clamps to get it free. I tried, but there was too much stuff in the way.

When the engine is up to temp 80-85C, and then shut off for 20 or 30 minutes, then restarted, the heat comes out the vents for about 5 minutes. Then the air flow into the cabin is hardly warm at all.

So when it sits, the hot fluid seeps into the heater core, but its not being recirculated when the engine is running.

funola · #38 11-26-2014, 10:41 AM

Quote:

Originally Posted by Gregory

..............
When the engine is up to temp 80-85C, and then shut off for 20 or 30 minutes, then restarted, the heat comes out the vents for about 5 minutes. Then the air flow into the cabin is hardly warm at all.

So when it sits, the hot fluid seeps into the heater core, but its not being recirculated when the engine is running.

There is a float valve in the monovalve which prevents the symptoms you're having. If you shake it, you should hear it rattle. It may be clogged or jammed. Clean it out by soaking it in CLR (calcium lime rust) solvent and see if that cures it.

Gregory · #39 11-26-2014, 12:37 PM

I removed the old monovalve solenoid and plunger. The plunger did not slide freely and the diaphragm was split.

I carefully examined the part I pulled yesterday from the 380SE. Its plunger slid easily and the diaphragm looked to be good. I checked the ohms on both coils, they were very close, 14.9 - 15.0.

I installed the used P&P part and test drove it for a half hour. The heater now works normally.

This car was a Cali and Arizona car most of its life, the heater was likely never used much. I think the solenoid was stuck closed and the split in the diaphragm allowed just a little coolant into the heater core.

Thank you Forum, this place is great! Fixed for $5.00.

steamboatsykes · #40 11-26-2014, 02:51 PM

Quote:

Originally Posted by funola

Was the MTC fit so tight that it hindered solenoid travel/ movement?

If you cut away the screen, you'll see the coolant has no place to go behind the screen, it can only go in then out the screen, which begs the question: what does it do?

Yes, perhaps. I had to force the metal part through the coil, for both of them.

I'll cut one of the replacement open and take a look as well. It would be interesting to find a flow diagram for the heating system. Perhaps it would make more sense then.

funola · #41 11-26-2014, 04:17 PM

Quote:

Originally Posted by steamboatsykes

Yes, perhaps. I had to force the metal part through the coil, for both of them.

I'll cut one of the replacement open and take a look as well. It would be interesting to find a flow diagram for the heating system. Perhaps it would make more sense then.

Something is very wrong if you had to force the "iron core" in.

Here's a link to a coolant flow diagram though it does not show the monovalve or aux water pump but you can pencil that in yourself by looking at your hoses. The flow (I believe) is from the heater core to the monovalve, down to the aux water pump, then back into the engine.

http://www.peachparts.com/shopforum/attachments/diesel-discussion/125934d1416765371-coolant-flow-direction-85-300td-coolant-circuit-617-20-005.pdf

funola · #42 11-26-2014, 04:20 PM

Quote:

Originally Posted by Gregory

I could not get to all the hose clamps to get it free. I tried, but there was too much stuff in the way.

...................

Next time, cut the hoses.

bradkaye · #43 12-02-2014, 02:43 PM

I found this thread after just replacing my thermostat, thinking it may have been the root of my non-heat problem at speed. It wasn't, but it will be a good winter thermostat registering about 10º higher than the previous.

New mono-valve went in mid-winter earlier this year and soon after fixing my problem initially, stopped delivering heat entirely. I had been running the car without the electric connection to the monovalve with either hot (idle or slow city speeds) or no heat at all (highway/freeway speeds) with a couple window down moments when it was over delivering heat around town when it was only mildly cold (30's) outside.

I pulled and checked the movement today and the spring action felt really light, so I grabbed a neodymium magnet from an old computer hard drive and stuck it to the top of the monovalve, increasing the resistance to pulling on the spring. I have heat in the car again at all speeds, illustrating the mechanical failure of a new monovalve having nothing to do with the electrical input.

It's the worst thing ever when new parts fail because you rarely look at it as the culprit when the problem you're seeking to solve is still present.