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Hello guys,
So, my in cab heater has been rolling the toasty heat out since I hit the road. The last two times I have started the truck up after about two minutes I noticed a light steam vapor spewing from the heater box. Uh-Oh I thought, core leak. I reached up into the heater and looked for a coolant leak. Nothing , bone dry. Nothing dripping on the floor. No sweet smell of hot coolant.
Yesterday the same thing. A light steam vapor during warm up, it last about a minute then is gone?Condensation? Now yesterday I notice the heater box is no longer getting warm, both coolant hoses going to it are hot but it appears the core in the heater box is barely lukewarm now at best with the engine at 160-180. I don't get the steam vapor issue, I took the sheet metal cover off to look for any type of leak, it appears dry. I checked the core before start up and it feels dry.
Is the heater core clogged perhaps? Thoughts?

Is your radiator still filled? Is there a shutoff valve on your engine for the heater?

Yes, coolant level is fine. Valve to heater is open.

HMMMM... WHAT YOU DESCRIBE, I HAVE EXPERIENCED WITH THREE DIFFERENT VEHICLES. IT TURNED OUT ALL THREE TIMES IT WAS A CORE LEAK. I HOPE YOU HAVE BETTER LUCK THAN ME.

Core is plugged. A good rad shop can usually "boil them out" if you take the core to them for service, if its in good enough condition to survive the caustic solution. You could also try soaking the core yourself in something like CLR - that might do the trick for cheap. Its probably also a good idea to flush the cooling system and install some new coolant. You might have driven the truck enough to loosen some scale and such.

Well if the core is warm and both the in and out hoses are warm then perhaps the return at the engine is plugged. The quick test is to remove the two hoses and blow thru the heater core. Or remove the return hose from the heater and plug it then install a piece of hose on the return side of the heater and run it to the radiator filler port and start her up and see what if any flow you get.

COULD ALSO BE AN AIR LOCK, TRY BLEADING THE CORE.
GOOD LUCK, BOB

Thanks gang. I figured a plugged core. I will investigate and let you all know

Once you have this up front issue solved; you might want to consider a coolant filter. It totally eleminates clogs anywhere in the system once in place and serviced properly. Most of the trucks we build get one; success rate as a result of having it in the system has been great.

MSeriesRebuild wrote:Once you have this up front issue solved; you might want to consider a coolant filter. It totally eleminates clogs anywhere in the system once in place and serviced properly. Most of the trucks we build get one; success rate as a result of having it in the system has been great.

I've often thought a coolant filter would be a great idea, but I've never seen one before. Is this a custom piece Charles, or are they more commonly available than I am aware of? Are they designed to filter all the coolant in a single pass, or do they filter only a small amount at a time?

Coolant filters seem to be more common in Diesels and Boats but are found on gas vehicle engines as well. Here's a good write up: http://www.dieselwarden.net/ford/coolfilter1.html

It certainly wouldn't hurt on a questionable older components system.

The coolant filters filter a little of the coolant at a time. They are normally installed in their own circut like a heater is installed. Using the same ports as the heater, just a seperate circut. Semi trucks have used these for many years, and are readily available from any big truck parts house along with the remote mounting bracket. You can also get these filters with a "recharge" chemical in them to replenish your coolants additives. Just make sure you don't get a "recharge" filter with too potent a recharge for your application.

Steve

I've seen the circuits done many different ways. It is not a good idea to plumb it into the heater circuit, this just impedes the flow; it needs to be in a free flowing circuit of its own. The best is to pick up the coolant flow from the block drain port, you can tee here and still keep the block drain cock operable. This sends coolant to the filter from the lowest point in the block which is where the majority of sediment will be found. It will make a huge difference in coolant cleanliness. If your system is really dirty, it will likely clog a filter element within an hour of operation; simply change out the filter and normally with 1 or 2 changes, the system is cleared of fine debris and flows freely. After the system is cleared of circulating debris, an annual filter change is good, even less often if the engine runs few hours. Filter heads & elements are available locally, NAPA, CarQuest has one that does ok. Baldwin offers a much better head design that has more choices of hook ups making these more universal as far as mounting options and locations. We install valves on ours so the filter element can be changed without draining the cooling system completely; just cut off the valves, change the spin on element, open the valves, top off the coolant, and you are done in a couple of minutes.

If you have a really dirty system that is already causing clogging issues, you will need to thoroughly clean and flush out the system before installing a filter. This may include removing the radiator and heater core; taking it to a repair facility for boiling and or rodding out. These filters really do work well, but they aren't miracle workers for filthy systems.

Well, well, well! I keep gettin' older, but I still keep on learnin' stuff! For instance:

(1) I never heard of an "air lock" in a heater system. I imagine it would be similar to a vapor lock in a fuel line, though, so I guess it could happen.

(2) I never heard of a coolant filter, either. I've owned/operated/repaired many gassers in my time and never encountered one. I've also operated many diesels in my day and never saw one on them, either.

Thank you, gentlemen, for keeping an old fart on his toes.

I have had my M37 for a little over a year, and have had to drain down the coolant twice. Each time, the coolant sat in a 5 gallon bucket for a while before being filtered and poured back into the radiator. Each time there was a rust colored sludge left in the bottom of the bucket. I am interested in a filter, and also in flushing the system. With these filters in their own loop, do they only filter a small amount of coolant which happens to get through them?