How long until you get hot air? - PeachParts Mercedes-Benz Forum

dhjenkins · #1 10-28-2009, 09:42 AM

My commute is only 2.5 miles, and takes roughly 6-7 minutes. While I do start to get warm-ish air by the time I get to work, it never gets hot, though the temp gauge gets to 80C. The ambient temperature is only 50degF.

It is, however, slightly warmer than the temperature of the air coming off the radiator from the fan (which isn't warm at all).

Yesterday when I drove it around for around 20 minutes, I put it on defrost and got hot air immediately, even at idle. When I pulled the plug to the monovalve, I got strong heat at every temp/vent setting (A/C is out as are some vent pods).

Since the heat comes directly off of the block, I would expect it to be that hot when it goes through the heater core. Is that not the case or is my commute simply too short?

#2 10-28-2009, 09:56 AM

It takes between 3 and 5 seconds after asking a politician a question until the hot air begins to flow.

Seriously though. I live in the boonies and it is 2.5 miles to the first stop sign from my driveway. By the time I get to that stop sign unless it is the dead of Winter, I'm getting some warm air. By the time I get to the end of my 22 mile one way commute I'm getting serious hot air if the ACC is asking for it.

Since I have no way of knowing what year and model car you are referring to, I can't take it any further.

dhjenkins · #3 10-28-2009, 09:59 AM

Duh. I always forget that part.

1985 (euro) 380SEL...

Edited my signature too...

babymog · #4 10-28-2009, 12:52 PM

About 3-4 blocks, '87 300D and '95 E320.

tinypanzer · #5 10-28-2009, 07:35 PM

It could be a torn monovalve diaphragm, but the fact that you get strong heat when you pull the plug might indicate otherwise. It's really easy to pull the diaphragm out and check for a tear, so I'd do that just to be sure, before moving on to what I am going to suggest next.

The CCU pulses the monovalve solenoid to allow in however much hot coolant the CCU thinks is needed to accomplish the temperature you have it set to. I'd start CCU diagnosis by testing the in-car temp sensor (in the dome light assy.) with an ohmmeter to make sure that its resistance corresponds to the temperature correctly. I don't have a chart for that sensor off hand, but I'm sure one exists. Basically, if the temp sensor thinks the interior is hotter than it is, it will not open the monovalve as much.

Turn the temp wheel all the way to hot until it clicks. That should make the monovalve open completely and stay open, just like when you pulled the plug. If that produces heat like you would expect, then you have either a CCU or interior temp sensor problem.

Still, I would start by checking the diaphragm and making sure it isn't torn. That is a typical fault with those. A flat blade screwdriver is all you need, it takes 5 minutes.

Also, the fact that your radiator isn't getting hot might indicate that you have a stuck open thermostat, in which case your engine will never get up to proper operating temps. If you're not getting to 80-85c on that 7 mile drive, then I would strongly suspect the thermostat (providing your dash temp display is accurate).

bsmuwk · #6 10-28-2009, 07:51 PM

around 6 minutes i get warm air, then when the car warms up a little more i get relatively hot air after around 15 minutes from start time.

i don't warm up my car. i start it, let it idle for a minute or so, then i drive off and keep the RPMs under 2000 until the temperature needles moves off the bottom peg and goes to the first temperature mark. afterwards, i gradually increase engine speed.

dhjenkins · #7 10-28-2009, 08:35 PM

Quote:

Originally Posted by tinypanzer

It could be a torn monovalve diaphragm, but the fact that you get strong heat when you pull the plug might indicate otherwise. It's really easy to pull the diaphragm out and check for a tear, so I'd do that just to be sure, before moving on to what I am going to suggest next.

The CCU pulses the monovalve solenoid to allow in however much hot coolant the CCU thinks is needed to accomplish the temperature you have it set to. I'd start CCU diagnosis by testing the in-car temp sensor (in the dome light assy.) with an ohmmeter to make sure that its resistance corresponds to the temperature correctly. I don't have a chart for that sensor off hand, but I'm sure one exists. Basically, if the temp sensor thinks the interior is hotter than it is, it will not open the monovalve as much.

Turn the temp wheel all the way to hot until it clicks. That should make the monovalve open completely and stay open, just like when you pulled the plug. If that produces heat like you would expect, then you have either a CCU or interior temp sensor problem.

Still, I would start by checking the diaphragm and making sure it isn't torn. That is a typical fault with those. A flat blade screwdriver is all you need, it takes 5 minutes.

Also, the fact that your radiator isn't getting hot might indicate that you have a stuck open thermostat, in which case your engine will never get up to proper operating temps. If you're not getting to 80-85c on that 7 mile drive, then I would strongly suspect the thermostat (providing your dash temp display is accurate).

I did do a little CCU diagnosis by using a temperature probe & my fluke MM, though I didn't test any resistance. After driving for about 20 minutes, I took the ambient temperature reading from the meter and set the rotary dial to that. When I did that, the heat shut off completely and the blower slowed down. When I decreased my set temperature, the blower sped up (however A/C is non-functional right now due to leak) and I got cool air (it was around 69 that day). When I returned the dial to the ambient temp, the blower slowed down again. When I increased my set temp., I got more blower and good heat.

I don't believe it's a stuck thermostat, because the last time I drove to work, it was pretty close 80-85 when I parked it. I then got the RPM's up to around 4k, and the temp dropped quickly down to 60, indicating that the thermostat must have opened.

Honestly, if I don't hit any lights, it's less than a 6 minute drive @ 35mph...

My '00 GMC Sierra barely has heat by the time I get to work, too. Of course, that's why I have remote start

pawoSD · #8 10-29-2009, 12:01 AM

The gasser I get heat in a few blocks.....or a mile or so. The diesel takes much longer, especially if its really cold out. I am tough, so I don't care.

tinypanzer · #9 10-29-2009, 12:35 AM

Quote:

Originally Posted by dhjenkins

I did do a little CCU diagnosis by using a temperature probe & my fluke MM, though I didn't test any resistance. After driving for about 20 minutes, I took the ambient temperature reading from the meter and set the rotary dial to that. When I did that, the heat shut off completely and the blower slowed down. When I decreased my set temperature, the blower sped up (however A/C is non-functional right now due to leak) and I got cool air (it was around 69 that day). When I returned the dial to the ambient temp, the blower slowed down again. When I increased my set temp., I got more blower and good heat.

I don't believe it's a stuck thermostat, because the last time I drove to work, it was pretty close 80-85 when I parked it. I then got the RPM's up to around 4k, and the temp dropped quickly down to 60, indicating that the thermostat must have opened.

Honestly, if I don't hit any lights, it's less than a 6 minute drive @ 35mph...

My '00 GMC Sierra barely has heat by the time I get to work, too. Of course, that's why I have remote start

Sounds like you did a pretty decent test of the CCU, the blower speeds and temp change behavior is correct as you noted.

So - You are getting good heat, just not in that short a drive, correct? If you drive further, you get good heat?

Perhaps the aux coolant pump is dead, if your car has one.

GregoryV022 · #10 10-29-2009, 01:44 AM

well in my 16 valve, it takes about 2-3 blocks to get hot.

try putting the recirculation. that way its heating already heated air. youll get hot air much faster, thats what i do for the diesels

compress ignite · #11 10-29-2009, 02:57 AM

Set it to start warming 3 hours before you leave...
Toasty hot Air as soon as you turn the key.

Short drives where the engine doesn't reach OP temp are horrible for the engine!

#12 10-29-2009, 08:38 AM

I'm sure you know that a torn monovalve diaphragm will cause more heat than you want, not less.

I'm also sure that it has already occurred to you that you could have a bad thermostat. I'm not sure how the V8 thermostat is arranged, but I fully expect that it has a bypass as the other engines do. I have had a few thermostats fail open, or in some cases not closed fully. If you haven't replaced the thermostat in a long time, it might not be a bad idea given that it is an inexpensive item.

dhjenkins · #13 10-29-2009, 11:39 AM

Double post

dhjenkins · #14 10-29-2009, 11:39 AM

Quote:

Originally Posted by tinypanzer

Sounds like you did a pretty decent test of the CCU, the blower speeds and temp change behavior is correct as you noted.

So - You are getting good heat, just not in that short a drive, correct? If you drive further, you get good heat?

Perhaps the aux coolant pump is dead, if your car has one.

Thanks!

Yes, if I drive further, I get good heat. My car does have an aux pump, but the heat stays just as hot letting it idle in park for a few minutes, so I don't think it's that.

Quote:

Originally Posted by LarryBible

I'm sure you know that a torn monovalve diaphragm will cause more heat than you want, not less.

I'm also sure that it has already occurred to you that you could have a bad thermostat. I'm not sure how the V8 thermostat is arranged, but I fully expect that it has a bypass as the other engines do. I have had a few thermostats fail open, or in some cases not closed fully. If you haven't replaced the thermostat in a long time, it might not be a bad idea given that it is an inexpensive item.

Yes, and yes, but see above. If it didn't close fully, I'd be able to feel hot coolant in the radiator hose. If it was stuck open, the engine coolant wouldn't reach operating temp by the time I got to work. Like I said, the temp gauge shows the stat opening, and this is verified by hot air coming off of the radiator once it does...

I drove my truck to work today, and I also did not have heat by the time I got to work, so I'm guessing it's just the short, straight trip.

Quote:

Originally Posted by compress ignite

Set it to start warming 3 hours before you leave...
Toasty hot Air as soon as you turn the key.

Short drives where the engine doesn't reach OP temp are horrible for the engine!

Is a block heater standard equipment? I live in South Texas, where it might freeze 10 days out of the year. IIRC, last Christmas it was around 55-60F, and I think the last time it snowed was in 1986.

The coolant inside the block does get up to operating temp by the time I get to work, though barely - pretty much right at or slightly below 80C. Of course, I run an ACEA approved full synthetic, so short trips aren't as bad for it as they could be.

I'm parking it for a while anyway. It sat for 2 years so I just wanted to put a tank of gas through it before I started tearing into the windows, A/C, vent pods, front end, brakes, engine, etc...