Backflush heater core

JohnM · November 13, 2018, 02:11 PM

Hi, I googled and read several threads completely, on no dash heat problems. I get some heat (edit very little, and only after the engine has been driven for 10 minutes), and anyway on the age of this thing, willing to do a backflush.

I've read where CLR was used: the entire system was drained, refilled with water and CLR, run for a short period, flushed. Refilled with 50/50

I've read where a poster insisted simply backflushing the heater core was enough. I'm wondering if it's possible to, instead of draining the whole cooling system and doing the water-CLR flush, to try first to run water backwards through the heater core only. My understanding is the heater core is the highest point on the system,

so starting with a cold engine, where do I look for the inlet/outlet for the heater core?

86 Itasca Elandan GM P30 454 Carbureted (stock), 45k miles.

Rickf1985 · November 13, 2018, 07:40 PM

The hoses will be right out front going into the side of the heater box. The safest way to do this is plan on replacing the hoses for a couple reasons, first they are old and should be done just to prevent a failure down the road. Second, to get the hoses off the heater core the safest way to do it is to slit the hose from the end back to the part that is not on the fitting, that way you can just peel it off the soft brass tube without damaging the tube. The supply line will be the one coming out of the manifold so you will want to attach one of the new hoses to the other fitting on the heater and run water into that one. You will be amazed at how much garbage comes out of the core. Then move the hose to the other side and run water the normal direction. Go back and forth until you get clear water both ways. No need for CLR, that just increases the chance for a leak in an old core. And here is a hint from an OLD mechanic, Use Permatex #3 sealant on all of the hoses to prevent leaks and also to ease the installation and removal later. While flushing you can use a garden hose at pretty much full flow but make sure it is not building up pressure in the core. Any more than 15lbs of pressure could pop the core.

JohnM · November 14, 2018, 11:41 AM

That's what I needed to know. When I take the cowling off, is the hookup (supply) on the top-right, passenger side near the front? Or?

Rickf1985 · November 14, 2018, 09:04 PM

I will look at mine tomorrow and let you know.

JohnM · November 14, 2018, 09:25 PM

Awesome.

I'm hoping to do this on the road.

Rickf1985 · November 15, 2018, 03:07 PM

OOP's! I just saw this and forgo to go look, it has been snowing all day. Give me 15 minutes.

I'm back, the supply on mine is the line towards the rear of the heater box. It will be the one with the control valve in it. Again, do not try to twist that line off of the heater core or you will probably break the core. The heater core really does not care which way the hoses are hooked up so you really need to check to be sure it is the hose coming off of the intake manifold. It is possible that when it was all put together that the hoses on the box were reversed from what mine are. I have also seen people put hoses back with the heater control on the outlet which is not correct. You want the first flush to be reverse and then switch back and forth till clean.

JohnM · November 15, 2018, 03:34 PM

Assuming I don't know where the heater core is, with the cowling off, the cover between the driver and passenger, where do I look?

I appreciate your help. But please assume I've never done this before.

BamBam · November 15, 2018, 05:29 PM

Your best bet is looking at the block/motor. There should be 2 hoses that are close to the front of the motor by the water pump. Follow those 2 hoses to wherever they go, when you hit the end that's your heater ends. There's so much on youtube that might help. Here's a start. Good Luck
https://www.youtube.com/results?search_query=gm+454+heater+hoses

Rickf1985 · November 15, 2018, 08:18 PM

All the way to the left side looking in from the front. Here is a pic of mine, heater is on the left with hoses going into it. Keep in mind that my radiator and AC condensor are out in this pic. Click on pic a couple times to make it huge.

JohnM · November 16, 2018, 09:20 PM

ok. Thanks for making the extra effort. I have to do this on the road, probably whereever there's a tap (dumpsite). I've been doing some interior carpentry after redoing the roof (trashed out). But when we had a cold snap and my heater was barely working... I knew I needed to ask and dig as deep as I could (or ask you to do), so I could take the next opportunity.

Rickf1985 · November 17, 2018, 11:35 AM

I would be glad to help but I see you are on the other side of the country from me. Post where you are and maybe someone on here could help you out. Considering the fact you are in the farther north area when you do this I would replace the lost coolant with at least a 75/25 mix of antifreeze to compensate for what you lose. That will even out what is in the system and probably has been there for a long time. On that coach you may also have the rear heater, have you checked that?

circleD · November 17, 2018, 08:38 PM

I'm late to this but like Rick said, cut the old hose and flush the core. If CLR isn't rinsed out completely it can become a corrosive and eat through what ever it sits in. I've always said and did it myself that we all have OLD RVs and it's best to spend a few more dollars replacing anything you can when working on a project. It keeps the odds in your favor. When I bought hoses or fuel lines I'd get more than enough as spare for others in the campground.

JohnM · November 21, 2018, 04:19 PM

Quote from: Rickf1985 on November 17, 2018, 11:35 AMI would be glad to help but I see you are on the other side of the country from me.

No longer in Montana. No economy, State limps along on tourism.

Might be closer to you. Will update location!

Rickf1985 · November 21, 2018, 04:24 PM

Well, temperatures are headed for the low teens for the next few days so you don't want to be anywhere near the northeast if your heat is not working! And flushing it in those temps is out, all hoses will be frozen solid unless you find someone with an indoor shop. I am getting a new hip on Monday so I will be out of the repair business for at least a few weeks. I can advise and point but I don't think the missus will allow me to turn wrenches.

TerryH · November 21, 2018, 08:04 PM

Quote from: Rickf1985 on November 21, 2018, 04:24 PM
I am getting a new hip on Monday so I will be out of the repair business for at least a few weeks.

Best wishes, Rick.
You've been waiting for this for a while, no?
Will it help with your back issues?
Please keep us up to date.

Froggy1936 · November 21, 2018, 09:12 PM

Best Wishes Rick , Frank !

circleD · November 24, 2018, 11:56 AM

I agree with Rick. Sometimes things are hard to find or change on the site but it has ALOT of organized valuable information. So please be patient and things will be fixed. By the way, we gave Mark the name Oz years ago because there is so much going on behind the scenes after his day job and personal life that we're glad he keeps this site moving forward for all of us.
Good luck getting the heater core flushed and I hope things work out for you while traveling. I'm in NC so I'm not much help either.

BrandonMc · December 29, 2018, 06:27 PM

do you have an auxiliary rear heater? you may want to flush that too, there's lines going to the rear of the rv in that case. I've been looking to do it as it was missed the first time the cooling system was drained.

JohnM · February 01, 2019, 11:59 PM

The flush:

First of all, locating a place to do this on the road was difficult. However, the local water dept has a free RV dump, where commercial sewage pumpers go (and must pay). We went when it was afternoon, and Friday, and payday (1st). There was virtually no traffic. I talked with a very smooth operator, the clerk/maintenance in charge of checking in commercial trucks.

He confirmed all the above or brought it up. He said there would be time to do it in one of the dump areas. I had gone on intuition, and yes, it was the best time. We had about 2 hours to flush, and it was over a special drain that went to the treatment facility.

Having my regular garden hoses, about 25' total, was enough, to feed the top of the radiator fill neck. There is a petcock facing rear, that you 'loosen' underneath the driver's side of the radiator. Using a wrench to provide light pressure to gently 'break' it loose, it was then easy to screw out by hand (lefty loosy).

When it's unscrewing, it's going IN, towards the radiator, as if you are tightening an ordinary bolt. i??

Nothing came out. No fluid. Hm?

I conjectured that the center, which is hollow and can receive a hose to direct the flow, was clogged. Sure enough, probing around with a pair of tweezers, crud came out, followed by very warm coolant.

Initially, with the motor off and not feeding new water, I drained it as much as possible. About 3 gallons of dirty, brown coolant came out.

Once, the drain hose plugged, about a few minutes into the initial gravity, fill-cap-off draining. It was removed, and blown out with the hose.

The initial drain fluid was captured in a container.

Switching to topping up the fill spout with the hose continuously, the drain valve was re-opened, with the hose filling the neck, slightly faster than the drain valve could empty. When the fresh water was replenished, backing up in the fill neck & spilling out, the engine was started.

The water was sampled. Eventually it went from whatever color originally (brownish) to a dark pee color. The pee color very gradually lightened up. Very gradually - 20 minutes went by.

With the cap filling continuously with cold hose water and valve draining, the heater core had become unclogged enough to provide good heat when the needle read 1/4 temp. It used to have to get to 1/2 temp, then provided little heat afterwards. I also noticed it was varying widely today, to 3/4 temp. Nominal temps and driving conditions.

The water was shut off, followed by the valve being closed with about a half gallon of missing water. 2 cups of CLR were added, and the fill neck was topped off with water.

With the cap off & CLR in, the engine was run at idle for about 5 minutes. Then we switched back to continuous freshwater, drain valve open, for another 20 minutes. Sampling the drain water near the end noting it turned less acid over time, and ended with just a light sweet taste of propelyne glycol.

Slightly yellow water continued to exit, but it was at the point where you had to collect it in a white bucket to see that it had yellow remaining. The stream by itself no longer appeared yellow.

After deciding that by taste, the acid had been neutralized, and wondering about adding a teaspoon of baking soda to further neutralize remaining potential acidity, a 3+ qt amount of water was drained, engine off, and replaced at the fill neck with a 50/50 coolant pre-mix.

It was all I had, and we'd only have to travel a couple of miles to go to buy concentrate.

It drove fine to the local store to buy more, and the dash was able to pump out heat.

Thanks to contributors on this forum who answered questions and made me confident I could manage this project.

I will be emptying watery coolant, and replacing that with concentrate. Anyone can suggest what the actual ratios are? Like is it two gallons out, 2 gallons concentrate in, 3? Because, then I will drain that entjre amount and top up concentrate equally.

Also what about the teaspoon of baking soda idea?

Edit/update: Realized I do have a compressor w/tank. Could run 5-10psi into the fill cap w everything (engine) off, drain valve open, to 100% purge the system. Disconnect and backpressurize the heater core to effectively backflush it. Then put it back together and pour a 50/50 mix of distilled + coolant in.

Rickf1985 · February 02, 2019, 08:56 AM

Ok John, Glad to see you got the system flushed but all that you did probably did not solve your heater problem. All you did was to run cleaner through the engine in the normal direction. This may or may not have put anything through the heater cores. What you need to do is to physically take the hoses off of the heater core and flush backwards first and then forwards through those hoses and that is what will get the crap out of the heater core. The coolant ratio is 50/50 so I would figure you have 6 gallons of fluid and start with adding 3 gallons of concentrate into the radiator and then add three gallons of water. You probably will not the full three gallons of water in but figure you still had residual water in the system. After driving it for a week or so test the strength of the antifreeze, it is much better to be to strong than too weak. It does sound like your original antifreeze may have been just that, original. It was definitely due for change. But I am afraid that the heater core may still be clogged.

You can never 100% purge the system without pulling the block drains. Adding pressure to the radiator is not a good idea. The coolant will only drain as low as the water pump inlet. I forgot to clarify if you have the rear heater? I said 6 gallons based on having the rear heater. If you do not have the rear heater figure a 5 gallon system and put 2.5 gallons of concentrate in the radiator.

JohnM · February 11, 2019, 01:52 PM

Got it thanks to you and other member's help on this thread.

I did try flushing it backwards by hooking the hoses up in reverse, but nothing really came out. Did the reverse hose trick, letting the system pump the heater core backwards, after already 20min+light clr in a normal forward motion, so whatever had been in there must be out. I don't remember if I did the reversing of the hoses before or after the final 20 min flush.

It now takes MUCH longer to get to even half temp, at outdoor temps of nearly 60, and the needle no longer floats up to 3/4 at times. After 10min high idle warmup, then tapping the accelerator to get a low idle, the needle is steady at 1/4.

For that temp guage reading, warm but not hot air, as expected, is coming out of the vent on HEAT setting. The defrost is again working too.

Rickf1985 · February 11, 2019, 02:32 PM

Now would be a good time to put in a new 190 degree thermostat. You should get heat fairly quickly, within 3-4 minutes. Full hot heat in even cold weather in 5 minutes. If that is not happening then the thermostat is either sticking open or it is opening too soon.

BamBam · February 11, 2019, 07:20 PM

Throw in a bottle of Prestone Rust Inhibitor in the system to help keep it in check. Good Luck

Rickf1985 · February 11, 2019, 07:53 PM

the proper ratio of antifreeze will prevent rust. I am a firm believer of less additives the better. That is as bas as gas line cleaners and antifreeze. 90% of the gas at least in the US has alcohol in it. THAT is exactly what the gas line cleaners and antifreezes are. That was great back in the days before alcohol but now it is redundent and can also end up giving you too much alcohol in the system and screw up diaphragms and lines.