Overheating until...

[SKnight]

I'm going to vote for a faulty gauge too. To be more precise, the sending unit for said gauge.

I'm reading that the light comes on at 220*. You pull over, shut it down, restart it within a few minutes and the temperature is back down to normal.

Here's what I would suspect is happening.

Your sending unit, depending on if it's a single wire or if it's a dual wire sensor, grounds the gauge (Or the positive feed if it's a dual wire sensor.) as it gets hotter. When you're going along in traffic or slowly it's going to get hotter since 50MPH air is superior to a fan no matter how efficient it is.

At 195*, it operates normally. At 200* the sending unit basically shorts out. It grounds the signal more than is called for. It could be a hard ground, it could just be sending a high signal. You pull over.

All seems well, you look around. Meanwhile the sensor cools that 5*, goes back to normal. You drive, get in traffic, it does it again.

Now, I'm not saying drive it. I'm saying that's where I'd look based off your description as I read it.

See if you can secure access to the top of the engine and have a thermometer handy, one that can go 300*. Infrared, contact, even a cooking thermometer will do.

Start it and let it "Overheat". Once the light comes on, go measure the metal right next to the upper radiator hose. You'll see a few degrees less than actual, you get 195* inside is actually 200*.

At this point, see if there's a difference between your thermometer and the gauge. If there is, I'd change the sending unit. If not, it's mechanic time.

[jbramhall]

Originally Posted by SKnight

I'm going to vote for a faulty gauge too. To be more precise, the sending unit for said gauge.

I'm reading that the light comes on at 220*. You pull over, shut it down, restart it within a few minutes and the temperature is back down to normal.

Here's what I would suspect is happening.

Your sending unit, depending on if it's a single wire or if it's a dual wire sensor, grounds the gauge (Or the positive feed if it's a dual wire sensor.) as it gets hotter. When you're going along in traffic or slowly it's going to get hotter since 50MPH air is superior to a fan no matter how efficient it is.

At 195*, it operates normally. At 200* the sending unit basically shorts out. It grounds the signal more than is called for. It could be a hard ground, it could just be sending a high signal. You pull over.

All seems well, you look around. Meanwhile the sensor cools that 5*, goes back to normal. You drive, get in traffic, it does it again.

Now, I'm not saying drive it. I'm saying that's where I'd look based off your description as I read it.

See if you can secure access to the top of the engine and have a thermometer handy, one that can go 300*. Infrared, contact, even a cooking thermometer will do.

Start it and let it "Overheat". Once the light comes on, go measure the metal right next to the upper radiator hose. You'll see a few degrees less than actual, you get 195* inside is actually 200*.

At this point, see if there's a difference between your thermometer and the gauge. If there is, I'd change the sending unit. If not, it's mechanic time.

That would be good information to collect, but here's a post containing the steps I'd need to take to get to my upper radiator hose and why I'm trying to wait a bit before I turn the rig over to the shop...

http://www.rvpics.com/forum/threads/...from-hell.451/

[jbramhall]

Originally Posted by Still Kickin

Here is the procedure to check if your clutch fan is operating at proper efficiency. You will need two persons to do this simple check.

Start the engine and observe the clutch fan operating. (it's spinning)

While you are observing the rotating fan, have the second person shut off the engine.

The clutch fan should spin, no more than one to two and a half complete revolutions, before coming to a complete stop.

If your fan continues to free spin for more revolutions than specified, after shut off, your clutch fan is not operating within design perameters, and needs to be replaced.

The fan needs to pull enough air past the radiator to properly cool the coolant when it circulates through the radiator.



Let us know how this test turns out.

I crawled under the engine while my son cycled it on for 30 seconds then off. Using a flashlight, I was able to observe the fan running for 30 seconds then, after he shut down the engine, the fan seemed to freewheel for well over 3 revolutions. Too fast to count the revolutions, but I would guess it freewheeled for 4-5 seconds.

So, I know this fan clutch failed your prescribed test, and I'm curious why that is indicative of a failure? I don't really know how the part works.

Thanks

JB

[SKnight]

Originally Posted by jbramhall

I crawled under the engine while my son cycled it on for 30 seconds then off. Using a flashlight, I was able to observe the fan running for 30 seconds then, after he shut down the engine, the fan seemed to freewheel for well over 3 revolutions. Too fast to count the revolutions, but I would guess it freewheeled for 4-5 seconds.

So, I know this fan clutch failed your prescribed test, and I'm curious why that is indicative of a failure? I don't really know how the part works.

Thanks

JB

A non electronic fan clutch has a viscous fluid inside it that flows through passages, the pulley spins but the fan essentially free wheels until needed. There's a coiled spring on the front of the clutch that when it gets hot it turns a valve closing off the passage which causes the fan to turn closer to the pulley speed, more heat, it closes more locking it up more.

When the engine is hot the clutch should be at least partially locked up, on shutdown that lockup should stop the fan pretty quickly.

Unfortunately there's nothing particularly easy about working on a motorhome engine, at least not accessing it.

[Still Kickin]

Originally Posted by SKnight

A non electronic fan clutch has a viscous fluid inside it that flows through passages, the pulley spins but the fan essentially free wheels until needed. There's a coiled spring on the front of the clutch that when it gets hot it turns a valve closing off the passage which causes the fan to turn closer to the pulley speed, more heat, it closes more locking it up more.

When the engine is hot the clutch should be at least partially locked up, on shutdown that lockup should stop the fan pretty quickly.

Unfortunately there's nothing particularly easy about working on a motorhome engine, at least not accessing it.

Well put SK. Your clutch fan is SPENT. You just saved a diagnosis charge from your repair shop. You do seem to doubt the advice that the forum members offer. Just an observation.
So, we are curious if you do use this advice, or proceed down a different path. Either way, we would like to know your outcome, so we all can refer back, if, or when similiar events occur.
Good luck.

[jbramhall]

Originally Posted by SKnight

A non electronic fan clutch has a viscous fluid inside it that flows through passages, the pulley spins but the fan essentially free wheels until needed. There's a coiled spring on the front of the clutch that when it gets hot it turns a valve closing off the passage which causes the fan to turn closer to the pulley speed, more heat, it closes more locking it up more.



When the engine is hot the clutch should be at least partially locked up, on shutdown that lockup should stop the fan pretty quickly.



Unfortunately there's nothing particularly easy about working on a motorhome engine, at least not accessing it.

Did I screw up the test by not allowing the engine to warm up to where the fan needs to run due to temp? I did this test at cold temp.

Regarding the ease of maintenance, the fan clutch is a part covered by the warranty I purchased with the used coach; so, I'll bring it in for this. Imagine the questions I'd have trying to replace the thing myself!

[jbramhall]

Originally Posted by Still Kickin

Well put SK. Your clutch fan is SPENT. You just saved a diagnosis charge from your repair shop. You do seem to doubt the advice that the forum members offer. Just an observation.

So, we are curious if you do use this advice, or proceed down a different path. Either way, we would like to know your outcome, so we all can refer back, if, or when similiar events occur.

Good luck.

Sorry if my questions seem to come from doubt. I'm a first time RV owner with a great deal of curiosity about how it works. I'm not sure how to better convey tone through typing, but I'm clarifying my understanding with questions, not doubting.

I'll report back after I get the rig fixed. My sense is it won't go into the shop until after the holiday at the earliest.

Respectfully,

JB

[SKnight]

No worries, ask away. You're not doubting me or anyone, you're asking questions looking for more.

And yes, with it being cold the test wasn't 100% valid. When stone cold the fluid is thick which is why they sometimes roar some on startup, that passes quickly but then the fan pretty much freewheels. In fact, do NOT try this at home, but you can actually hold the fan completely still with the engine running when it's not needed.

Again, do not try that. It can and will take your fingers off.

Let the engine fully warm up and run for several minutes. That gets the clutch hot and locked up. Then try the shutdown test. It should smoothly stop pretty quickly.

[jbramhall]

Originally Posted by SKnight

No worries, ask away. You're not doubting me or anyone, you're asking questions looking for more.

And yes, with it being cold the test wasn't 100% valid. When stone cold the fluid is thick which is why they sometimes roar some on startup, that passes quickly but then the fan pretty much freewheels. In fact, do NOT try this at home, but you can actually hold the fan completely still with the engine running when it's not needed.

Again, do not try that. It can and will take your fingers off.

Let the engine fully warm up and run for several minutes. That gets the clutch hot and locked up. Then try the shutdown test. It should smoothly stop pretty quickly.

Well, now, this is going to get complicated. I suspect that my fan is not coming on when needed; so, I'm worried that I won't be able to get to proper test conditions by idling in the yard. I'm going to give that a try, however. I might need to drive it to the temperature warning level to get the fan to engage, then observe the behavior at shut down.

Any idea how hot is hot enough for the fan to engage? Is it a physical change from heat that makes the spring work, or some kind of feedback logic that triggers it to engage? Does the fluid in the clutch require occasional maintenance?

[SKnight]

The clutches are sealed, so no maintenance.

They go faster as the area gets hotter. They're always spinning the fan some so that air will be drawn to give the spring a temperature reference.

The fans move enough air under normal conditions you won't hear the fan, until it gets really, really hot.

It's strictly ambient heat, as the air in the area warms up the spring causing it to expand twisting the valve, the fan speeds up, more air is moved and the radiator cools off, the spring cools, contracts, opens the valve and releases the clutch some. This takes a load off the engine and improves economy and preserves parts because that fan is a really impressive piece

There are electrically controlled fan clutches, a motor takes the place of the spring and it's all computer controlled. They can go from literally sitting still as the engine idles to nearly fully locked up and moving air like a propeller.

[jbramhall]

The fan clutch failed the spin down test when hot. Also, it's making noise now that I know what to listen for. Sort of like a belt slipping, smells like new brakes. I'm going to get it in the shop ASAP rather than press my luck. Thanks to all for saving me time, I think the mechanic can safely assume that fan clutch is shot and maybe pre-order the part before I get there. I'll fill you all in here when it's fixed.

[Still Kickin]

Glad you learned something from all the give and take. If you want humor reseach this subject on youtube. It shows "the resident idiot" putting rolled up newspaper into spinning fan blades, to try and test the clutch fan. The method I related to you, seems much safer. Now, the next time someone talks about overheating issues, like the one you expierenced, you will be able to explain the test procedure, and know why and how a clutch fan works.
Be well and happy RVing.

[jbramhall]

I'm camping for the first time since getting the 390 BH back from the shop after 3 weeks in. Let me just start by saying the service contract I bought with the used coach was some of the best money I ever spent! $6,000 in covered repairs later, here's what was addressed:

Top side engine hatch opened from the bedroom (those of you who know, this is not easy)
Fan clutch replaced
Dash AC compressor replaced (it seized up)
Dash AC condenser/dryer replaced (also shot)
Drive belt replaced (seized AC compressor must have caused the belt to break, which didn't help my cooling problem!)
All coach leveling and slide hydraulic lines replaced (original ones were "sweating" fluid, indicating impending failure)

So, in keeping with my original post, the fan clutch was in fact bad. I'll never really know why I was getting intermittent cooling from it as opposed to a full failure, but at least my wife and I got a couple of relatively problem free trips in during April and May before we dropped it at the shop. I just towed my car with the whole family to Pittsburgh from the Jersey Shore in 90 degree heat, and the engine cooling and dash AC are solid.