Technical Inquiries: February 2002

Coolant Countdown

Q: Recently, a coolant hose failed on our 15-month-old motorhome built on a Spartan chassis. The hose, labeled “SAE 1527 J USCG Type 2,” was severely cracked. Although motorhome owners should check all their hoses regularly, if the coach has a coolant hose with that label, perhaps it should be checked carefully. If no cracks are readily apparent at the bends, the hose should be flexed to determine whether any cracks appear. If cracks show up, I suggest that the hose be replaced, even if it isn’t leaking. Our leak went from two drops per second to a small stream in no time at all. Fortunately, we discovered it at a rest stop and were able to get to a repair facility without overheating.

Larry Fuhriman, F250023
Cincinnati, Ohio

A: Thanks, Larry, perhaps other readers will benefit from your experience.

“” J.B.

Q: I have a “stinking” problem I hope you can help me with, namely my black water holding tank. The odor from it is unbearable each time the toilet is flushed. I have tried several brands of chemicals, even doubling up on the application. When I empty the tank, I flush it for as long as 30 minutes with the RV Hydroflush. I don’t know whether the problem is sewer gas or strictly the tank itself. My sewer hookup appears to be okay.

The unit is permanently parked as my full-time residence and cannot be moved so water and chemicals do not get sloshed around in the tank as it would if I were traveling with it. The unit is only three years old, and I have had this problem for more than a year. Any help you can give me in solving this problem would be greatly appreciated.

Owen Bush, F280527
Dade City, Florida

A: We’re taking a shot in the dark, Owen, since you didn’t give us your coach make and model or toilet manufacturer and model, but our first suggestion would be to check the outside vent tube. Be certain that the vent cap has sufficient clearance to allow the stack to “breathe,” and make sure that no birds or insects have blocked it with a nest. You also might try flushing the toilet about 12 times in quick succession. The built-in overflow tube in a Thetford toilet can sometimes lose its water seal, and the quick flushes will replenish it.

Since you’re full-timing in your motorhome, and it is stationary, how do you control the holding tanks? Do you leave the valves open or closed? Even with the coach parked and hooked up to a sewer line, the black water tank should always be closed until it’s time to empty it. If it remains open, all the fluids are immediately drained off and the solids remain to become more solid. Keep the black water tank closed and the gray water tank open until such time as you need to drain the black water tank. At this time, close the gray water valve until the tank is nearly full, and then drain the black water tank first. You can then drain the gray water “” this helps flush out the sewer hose.

It appears that you’ll probably have to call a plumber to break up all the solids and completely clean your tank so that you can start fresh.

“” J.B. & E.P.

Q: We have a 1988 Southwind 33L with a Chevrolet 454 V-8 engine. It runs great with the primary barrels of the carburetor open, but if I press down on the accelerator enough to open the secondary barrels, the engine loses power and will try to stall. If I let up on the accelerator, it picks up power and runs great. It does this when the coach is climbing a hill or on flat land if I try to pick up speed quickly.

We have replaced the spark plugs and checked the wires and have replaced the distributor cap, rotor, and fuel filters. The motorhome has a regulator at the tank where the line passes through the chassis frame; a large filter on the frame behind the entry steps; and a filter at the carburetor inlet. We replaced the fuel pump and isolated the fuel tank with another fuel supply, all to no avail. A mechanic checked for vacuum leaks, checked the vacuum advance, scoped the ignition, and checked the fuel pressure “” he said everything was okay. He rebuilt the carburetor, checked the ignition timing, and checked for slack in the timing chain and gears. I replaced the EGR valve, and I even drove with the gas cap off to relieve possible backpressure in the fuel tank.

The mechanic thinks the carburetor should be replaced, that there could be a crack or something wrong that the rebuild kit couldn’t fix. Do you have any ideas before we spend the cash for a new carburetor?

Dan and Mary Crain, F168022
Las Vegas, Nevada

A: It definitely sounds like fuel starvation, and you’ve done a thorough job of going through the system. My advice is to check for vacuum leaks in the fuel line and at the base of your carburetor, and to check the system’s vital signs under load even though you don’t have the electronics of the newer coaches. My pick would be the in-tank fuel “lifter” (a pump that assists the engine-mounted fuel pump on longer-wheelbase chassis) or more likely, the carburetor. Did your technician check and clean the filter inside the carburetor? The Quadrajet is a great carburetor, but it can be very tricky to service, test, and diagnose, as your mechanic already has recognized.

“” E.P.

Q: In May 2000, I purchased a 2000 26-foot Gulf Stream type C motorhome from Watts RV in Kent, Washington. We’ve had some problems with this coach, from loose bulkhead panels to broken wiring. All problems have been fixed except one: the Thetford toilet and black water tank interface.

Initially, the piping was installed incorrectly. The black water tank was routed to empty through the smaller valve, and the gray water was sent through the larger valve. Watts RV fixed this problem.

The second problem is at the toilet, where the pipe from the toilet enters the black water tank. The toilet is so far outboard that where it penetrates the tank top less than 2 inches of clearance exists from the underside of the pipe grommet to the bottom of the tank. This allows solid waste to back up to the underside of the toilet valve. To prevent this from happening, we have to use a whole bowl or two of water each time we flush. With only a 35-gallon holding tank, it is almost impossible to dry camp for any length of time. (We do use Thetford tissue.)

Watts RV officials tell us that this is a Gulf Stream design problem, with which I agree. Gulf Stream representatives indicate that it is a toilet/tank interface item and that everything is in the correct location. I have e-mailed Thetford to find out what can be done and if there are any code requirements for clearance at the pipe bottom. A representative at Thetford said that someone would get back to me, but no one has so far.

What can be done to alleviate this problem, and are there any construction code requirements for this installation? If so, what are they?

David E. Todd, F279221
Bellevue, Washington

A: The question I have is whether there is an extension pipe that goes down into the holding tank or whether you are saying that the point where the pipe enters the top of the tank is only 2 inches above the bottom. If the first is true, removing the toilet, flange, and extension pipe and then shortening the pipe should remedy the condition. If the second condition is true, perhaps the tank is installed in the wrong position or turned in the wrong direction. In any case, the toilet manufacturer has nothing to do with the installation beyond the point where its equipment attaches to the flange at floor level; the flange, pipe, and tank are installed during manufacturing of the coach. Is your dealer affiliated with Gulf Stream? If so, the dealer should be able to remedy the problem. If not, contact Gulf Stream and ask its representative to recommend a dealer that can resolve the problem for you.

“” E.P.

Q: I have a 1985 Mallard type A motorhome on a Chevrolet P-30 chassis. I need to replace the five-prong rocker switch that operates the headlights and running lights. Any suggestions on where I can find this switch?

George Blatchley, F69030
Mount Clemens, Michigan

A: I’ve got good news and bad news for you, George. The bad news is that you are the proud owner of an “orphaned” coach, which means its manufacturer is no longer in the motorhome business. Even worse, the company no longer makes parts or provides service information. The good news for “orphan” owners is that in most instances, including yours, key components are almost always standard production parts that are still available “” you just have to search them out.

I’m not certain whether Mallard used a relay to do the actual switching on that instrument panel, so I would go with a heavy-duty switch. A good source would be a company that furnishes parts for emergency vehicles, such as police cars, wreckers, and ambulances, which require a great deal of lighting. If you have a problem locating the switch, call Able2 Products Inc. (800-641-4098) “” part number 05-0509, lighted rocker switch, might fill the order as well as the opening in your dash. Part number K5AD321HPB from Otto Controls could also be a candidate (847-428-7171).

“” E.P.

Q: We have a 1993 Winnebago Elante with a Chevrolet 454 V-8 engine. We bought this unit last winter and had no problems with it until the warm weather came. It first started acting as though it were starving for fuel at interstate speeds. I replaced the fuel filter, which had a lot of debris in it, and this cured the high-speed problem. It still has a hesitation, however, whenever starting from a dead stop, which goes away at approximately 30 mph. The hesitation seems like the engine gets fuel, and then doesn’t get fuel. If I let off the throttle, it idles fine and doesn’t cut out.

Last July we started up a 6-degree grade and had to stop, because the engine became starved for fuel and overheated.

I have since removed and cleaned the fuel tank, checked the fuel pump for debris (it was clean), and replaced it anyway. I replaced the fan clutch since it was not engaging above 210 degrees Fahrenheit. I replaced the fuel pressure regulator and the sender in the distributor. I made a heat shield for the fuel lines at the frame-to-engine crossover. I checked the fuel pressure, and it is relieving at 14 psi. The engine temperature varies between 195 degrees and 210 degrees, for no reason. The engine has been examined on a tester, and no errors or out-of-range readings were found. There is a PROM update for the transmission shift, but it hasn’t been done yet.

This seems like a vapor lock problem. From a dead stop, it bucks as if it is fuel on, fuel off. While at highway speed, I can hold the throttle on the floor and increase braking until the motorhome is doing about 35 mph. Then it downshifts into first gear, and starts surging immediately.

John Lumley, F289834
Greenwood, South Carolina

A: It sounds to me like a fuel system problem. First, take a drive with the fuel filler cap loose to be certain that the tank is venting properly. Next, check for air leaks at the fuel filters and the filters themselves. I realize that you have changed one, but there may be others “” likely in or near the fuel tank.

The 14-psi fuel pressure is on target for your throttle-body fuel injection, but does it maintain that pressure under load? Most GMC truck service departments will have a monitor that can be attached and give code readouts during over-the-road conditions. If you can’t locate a dealer with this equipment, try to find a truck service shop with a chassis dynamometer and up-to-date analyzers “” and a competent technician to use this equipment. Either of these should be able to pinpoint your problem quickly without the expense of unnecessary parts replacement.

I would definitely have the PROM update done, and it’s not entirely impossible that some of these symptoms could be related. The 195-to-210-degree readings for your coolant temperature could be within the normal opening/closing range for a 195-degree thermostat, depending on the accuracy of the gauge and the point where the readings were taken.

“” E.P.