Dash heater barely working

My heater worked much better at low speeds than it did on the highway. I finally decided that too much outside air was getting in at highway speeds so I simply made a cover for the air intakes. That solved my problem but as wa8yxm the heater seems to be designed for a car, not a house. In cold weather I still have to run the furnace. It is on my wish list to put another heater about 10ft back, running the same water through it.

ANother issue is the design of the heater.

THe dash heater is designed to heat the cab of a Straight truck or Pick up truck

NOT A HOUSE.

1. In the old days, when a engine tstat "Failed" it was because it stayed OPEN and the water flowed thru the radiator with no restriction and the result was Cool/cold Heater output. The tstat in Gas engines acts as a restrictor also. If it failed CLOSED, your engine would then overheat
2. Motorhome Heater controls are all after market. The only thing the engine does is send the hot water forward to the Dash Heater assbly
3. So, if your dash gauge shows correct temp range, your engine/tstat is not the culprit
4. Unless you have had some type of work done on the engine, the manual coolant valves at the engine should not be a concern
5. The most COMMON cause of your problem, is the Dash AC Heater Control valve. It has probably failed or is clogged up. You need to go open the front hood and find and post the BRAND of the Dash AC system. IF you have an Evans Tempcon system that is easy to fix. But, Tiffin started using the Denso system years ago and I think you have that brand. Doug

Open the front and check to see if heat is making it up front. It shouldn't be hard to find the hoses. They'll connect to a valve, see what return line feels like. Years ago we had a valve stick, it didn't make heat or cool very well. It was an EvansTempcon valve that was defective. We replaced the valve, problem solved.

mikestock wrote:
I know that in my old gas burning cars the failure of the dash heat to warm up was almost always due to a bad thermostat. That may well be the problem with my 2006 DP, Cat 350 Phaeton. Naturally, changing out a thermostat in this engine is a major ordeal. The dash gage shows the coolant temp to be about normal, in this case I'm just wishing and wondering if someone knows of any other (hopefully simple) defect that can cause the heat to be only mildly warm.

Mikestock,
First, your statement that problematic dash heat in older cars was/is a bit off. In most of yesteryears cars/trucks etc. with either vacuum or manual controlled heater valves, it was those valves that often failed. Especially the vacuum controlled ones. Since they quite often weren't used during off season, as in summer, they'd freeze up. You had heat to them, but not beyond them. Even the manual heater control valves got difficult to move periodically. Yes, a thermostat occasionally went bad too but, they had two ways to go bad.

Now, as for your CAT equipped coach, well, in many cases, there are two, 1/4 turn valves in the heater hoses emanating from the engine and traveling to the front of the coach. They normally are around the oil pan area part of the frame but, they can be located elsewhere too. You don't say if this has been a problem from season to season so, at this point, it's probably not either of them but, it's worth a check to see if they're completely open or, parallel to the frame.

Most dash heat in diesel pushers is not substantially hot anyways due to the length of travel for the coolant. Even if and when the coolant lines are sufficiently insulated, they still cool down some on the way to the front of the coach. You'll still get some heat out of the dash heater but, not as much as a front engine coach. Our coach, an '04 Itasca Horizon 36GD with the C-7 330HP CAT, just took us through some snow covered country in the eastern section of So CAL and the outside temp at that time was 41 degrees.

The dash heater still worked but, even at high speed of the fan, it was not nearly as efficient as say, a car or pickup etc. with the engine up front and heater lines only a couple of feet long. And my heater system is in great shape and, I just changed both "Regulators" (that's what CAT calls thermostats) (and yes, there are two of them sitting side-by-side in the same housing).

My radiator is at peak efficiency too as I just had it out and thoroughly flushed it. So, at this point, make sure all heater line valves are completely open and, with a trusty infrared heat gun, (you can purchase one at most auto parts stores or, even Harbor Freight) and run a check of those heater lines all the way along the coach bottom to see how much heat loss you're experiencing in your particular heating system. And, you can make sure your heater ducts and heater core is also functioning as it and they are supposed to. Rarely do CAT regulators fail. Good luck.
Scott

We just drove down from northern California through rain, snow, and hail with no dash heat (And no Aqua-Hot heat either, but that's another topic). It turns out the vacuum-actuated device that controls where the heat goes; dash, defrost, lower vents, etc., had failed. My diesel shop discovered the part was a Ford part. They were able to replace it and we now have dash heat. Wife and cats are happy.

Pat in Menifee, CA

And, if you have motor-aid water heater, often they will have a valve that shuts off coolant water to the water heater and sends all of it to the heater core.

And, next thing I would do is verify that valve at heater core is opening all the way.

#1 failure mode is low coolant level.

If not that then follow the previous posts
Water Valve.
Back flush heater core.
If the thermostat was bad the temp gauge would never rise.

Have you checked the temp at the heater core? Could be that there is a shut off valve in the line going to the heater core. Could be the blend door of the heater is not opening to let the hot air in. Could be any number of things other than the thermostat. Do you have a temp reading gun or can you borrower one. If so I'd take readings of the hot water line from the engine to the heater core and see where you're loosing the heat.

Im gonna take a wild guess and say heater core is somewhat plugged. Back flush with compressed air and water. This is the tool pros use.
Heater Core Flush tool

If this does not work there is a flow valve somewhere blocked or closed. Worst case is blend door motor malfunction.

Whats the coolant condition? this maybe the indicator for elevated corrosion that made its way to the heater core. Also if you can feel the hoses if they are hot off the engine and cool coming back definitely heater core plugging.

Thermostats that go bad usually dont warm up at all even on the gauge or get over heated (rare)