Heater core flow test possible?
 

I was told our heater core is likely getting slowly plugged up and this is causing a slow flow of coolant through it. Its an 85 300TD
Just wondering if there is a way to test if this may be true or not? Perhaps there is a flow rate at which coolant passes through it or something, and could it be done by the home mechanic with basic tools?
Getting ready for our central canadian winter!
Thanks

Hiya neighbor,

I haven't seen publicly published "flow rate" numbers for any automotive heater core. You'd need to isolate the core from the rest of the system if you want to test the core; meaning a pump, pressure gages (two), a flow meter and some sort of closed reservoir container that can handle the pressure of the pump. Get that all set up and you still don't know what is "normal."

You may want to consider:
1. Cleaning the coolant system. I have learned (the hard way) to use an off-the-shelf cleaner at half strength, followed by a really good flush. Really good means draining the cleaner via the radiator AND block drains, refilling with water, running the engine, draining, then repeating the water flush until the water comes out clear. This may take a day, and half-strength on the cleaner has meant (for me) no more self-caused pin hole leaks in the core.
2. Checking and cleaning the air passageways. Critters (spiders, mice, etc.) have a habit of bringing their treasures into the passageways. I use zip-lock sandwich bags to keep the various screws sorted out, and put a note into to bag stating where the screws go. Check the operation of the dampers (and their seals) as long as you're in there. It may be time to change the damper seals. This will take at least a day on a "modern" car like yours.

Good luck, and enjoy our heat wave.

Brrrrrr!
 

It should be possible to drain the coolant system and then disconnect the heater hoses where they go through the firewall. Make sure the monovalve is out of the circuit and then connect extra hoses to the heater core. Now you can run water from a garden hose (gently!) to see (a) what comes out, (b) is the core plugged up, how badly, etc. and (c) how easily the water flows through the core.

If the core is badly crudded up and limiting the water flow, you'll have to put the system back together and run cooling system cleaner through the whole system. I once had an Alfa Romeo with a completely clogged heater core; fortunately it was easy to take apart so I could take the core to a shop for cleaning. The Mercedes core is a lot harder to remove--involves pulling the dash, I believe.

Once you have a core that flows well, make sure all the other components are working properly, especially the aux coolant pump and the monovalve. Flush the entire system and add factory-type antifreeze and distilled water to the strength required for your climate and may God have mercy on you and your diesel. Winnepeg! I was born in Duluth and that was bad enough. :D

Jeremy

Columbus was told that the Earth was flat. You might want to disconnect the electrical connector to your monovalve and then see how well your heater works.

Assuming that the monovalve or its associated controls are not your problem, simply drain enough out of the cooling system so that you can disconnect both heater hoses. Connect a garden hose in the reverse direction and back flush the junk out of it. This will almost always clear it out, BUT OCCASIONALLY doing this to a heater core will cause it to blow out requiring replacement.

The odds are heavily in your favor that you can simply back flush the heater core and everything will be fine with it, but if you're unlucky you will have a mess and the ABSOLUTE NECESSITY to replace the heater core.

Are you a risk taker?

I guess the risk is the higher pressure of the garden hose (30-60 psi) vs. the cooling system pressure (less than 20 psi)? You could put one of those small disk (the kind you use with soaker hose) on the garden hose when you connect it.

He did come to an internet forum for vehicle maintenance advice.

Most garden hoses have a valve on at least one end that works incredibly well when it comes to regulating pressure.

If the heater core was about to blow and backflushing takes it the rest of the way I'd consider that a good thing... Better then to have it blow up while you're far from home!

-Jason

There is no risk. The risk here is not to take the risk. You only get any pressure if the core is 100% blocked. It that WAS the case then the weakest point will burst and you know the core for sure is due for a replacement. If it did burst then it is only water and it will dry out:). You can forward or backward flush and it should not make any difference.

Hopefully any blockage will be flushed out.

Good luck.

That is factually incorrect.

And so is that.

What engineering school did you attend?

I have never been to any engineering school. But I know how to maintain diesel MBZs and run them for next to nothing. All we need is common sense.

The issue here is that some honourable members are so vindictive that nothing I posted in their eyes are correct.

You do not need to go to Berkeley, Stanford or MIT to know that pressure is caused by restricted flow. If the output is not 100% blocked and if the input is less than the output then you would have NO pressure build up.

Do we need accreditation to post in this forum?
 

I have never been to any engineering school in US but I went to a great one in UK, this is, United Kingdom just in case our honorable member do not know.

If one turns on the garden hose very gradually to back flush the heater core, there will not be any pressure build up if the outflow is greater than the inflow. If the core is 100% block then even a trickle will pressurize it as liquid is incompressible. Once the water comes out then one can increase the flow. As I have said, there is no risk to back flush the core.

Very good point. I was only trying to point out is the possibility that there could be a very large job that follows this very small one.


In response to one comment, it DOES INDEED matter whether you reverse or forward flush. In many cases forward flushing can just jam up the log jam tighter. Often reverse flushing will clear out what forward flushing will not. BTDT.

$0.02
 

The core is not a filter where back flushing is necessary. If all thing is being equal, backward or forward flushing the core will not make a significance difference. If something is lodged in there, which is unlikely, then back flushing may dislodge it but it may jam in the other direction. I have never removed a heater core but I would assume they are symmetrical like an evaporator so jamming in the other direction will be a possibility. IMHO, it is very unlikely something is jammed in there. If there is any problem with the core at all it is just caused by deposit which restricts the flow. The bottom line is that flushing it, hopefully, will remove the deposit. If it was my car, I would connect the garden hose in BOTH direction to make sure the flow is OK from both ends.

my $0.02