I have a 1996 motor home with the 460 EFI. Question is has anyone ever experienced a water pump failure where there is no leaking coolent? All cooling components are new except for the water pump. Engine will idle at 190 degrees all day long but will heat up on the highway to around 230 degrees within 2 miles. Pull over and the fan clutch will come on and cool the engine back down to 190 degrees. Radiator is new and the correct one. I'm starting to think the impeller has been damaged and will not move coolent efficiently at highway speeds. What do you all think? Tom

 

That would be a likely failure if you had a plastic pump impeller, but I don't believe 460s have those. I take it you changed the thermostat, and tested that the new one worked before fitting it. For some reason I've had more thermostat failures on my 460 motorhome and truck than on any other vehicle I've ever owned.

Does this motorhome have a Motoraid? How is the duct work to stop cooling air bypassing the radiator. If it overheats, does the heater still work?

Michael

 

New proper radiator (old one was leaking), new fan clutch, new thermostat (195)checked before installed, new temp gauge sendor, new radiator cap, hoses good with spring in lower hose, and the system is not losing coolent. The engine will sit and idle for hours at 190 degrees. Within 2 miles of highway speeds (60mph) the water temp will go to 230 degrees (factory gauge to the high mark of normal. The only thing I can think of is the water pump does not move the coolent efficently at hihway RPM's. Pull over to the side of the road and the fan clutch comes on the the temp goes right down to 195. I'm lost? Tom

 

Tom,
I found you had posted about lots of related issues with this vehicle, possibly explaining why you didn't really answer my questions.

As you probably know, the first thing to establish is whether it really is overheating. you seem to know that there are 2 sensor, one for the ECU and one for the dash gauge. I gather you've replaced the dash gauge one, and it still says the engine is too hot, but I believe I also read that your mechanical gauge says it's fine. Which are you going to believe?

You have 2 other options. One is to get an OBD-1 scan gauge, and that will allow you to tell how hot the computer thinks the engine is. You can also get infra red gauges very inexpensively these days. I have a 8 year old $70 one and a 3 month old $7 one from Harbor Freight. You can point that closely to a heater hose which is in the bypass circuit. There are also less scientific ways, like turning the heater on full and seeing how hot the air is. You may also have a motoraid which will cool the engine still more. And if it really overheating, it will eventually push coolant out of the radiator into the overflow tank.

If you drive the motorhome, and you believe it is overheating, then you certainly should turn on all heaters to full hot, because that will provide extra cooling.

If you're handy enough to attach mechanical gauges and drill out exhaust studs, you should certainly be able to let your engine warm up with no radiator cap on, and with an alternate top radiator hose connected from the thermostat housing to a large bucket. Keep the radiator topped up with water, and when the thermostat opens there will be a flood of water through the top hose.

Although I'm not there, I'm not yet convinced that it is overheating if a mechanical gauge says OK, and an electrical one says too hot. Maybe there's more evidence i haven't read.

Michael

 

Michael, I did attach a mechanical water temp gauge to the out going heater core hose. When I did a test drive the first time, I did not have the heater on so the coolent was not flowing through the heater hose. The temp under this condition was around 190 all the time. On my next test drive I turned on the heater which opened the valve and allowed the coolent to flow through the heater core system. This resulted in a water temp on the highway of 230 degrees within 2 miles of highway driving at 60 mph. Pulled over and the fan clutch engaged and the temps came back down to 190 and stayed between 190 and 210 in city driving. Fan clutch engaged at around 205 to 210. I'm going to do a compression test next to see how this goes. Will not be able to do this for 2 weeks as I'm going out of town. As I said the cooling system is not losing any coolent nor does it appear any oil is in the system. The engine seems to be running just fine and has good power. In addition there is "HOT" air coming from the heater. Thanks for your help Tom

 

Tom,
Thanks for the extra information; it helps.

How much history do you have with this motorhome? What I'm getting at is to try to see if these symptoms arrived along with some other problems. I gather the current overheating is since you've had the radiator replaced, or was overheating the reason you had the radiator replaced?

If we accept that it is overheating, then it can be either insufficient water flow as you currently suspect, or insufficient airflow through the radiator.

On the theory of testing the easy things first, I would suggest getting an IR temperature sensor, and testing the temperaure of the heater hoses, and the radiator top hose and bottom hose while the engine is idling. That should be easy, and very informative. I would not rule out the possibility of a stuck thermostat, even though you tested it before putting it in. But do the IR test first,

Also do you have the RV manufacturer's baffle that stops air flowing over the top of the radiator. Mine was missing, and the fan would clutch in at absurdly low road speeds on warm days. That's not enough to explain all your symptoms, but could be contributing.

Either with the IR sensor, or by hand, you should be able to feel the top hose warming up quite rapidly when the thermostat opens.

Michael

 

Micheal I have owned the motorhome since 2002. It is a Newmar Mountain Aire. I never had any overheating issues with the coach.; The radiator was replaced because the plastic end tanks were leaking. The over heating at highway speeds started after the replacement. I did try some stop leak before replacing the radiator. All of the rubber molding has been replaced around the radiator so the incoming air will go through the A/C condensor and then the radiator. When the heater is on I get hot air. When the A/C is on I get cold air. Many have told me it has the wrong radiator but the shop who replaced it says it is the correct one. I will try the IR temp readings and send them back to you. Tom

 

Tom,
It sounds like your air flow is in good shape then. Assuming the radiator is of approximately the correct size to fill the opening, it is hard to believe that even the wrong radiator would allow overheating that quickly. Of all the water flow limitations, the pump impeller, although possible seems the least likely.

I think the IR gauge testing is the way to go. I would think the thermostat could still be a suspect.

Do you believe the shop that replaced the radiator is competent? I am currently rebuilding a 460 in my 94 Winnebago because the shop whose owner and foreman I carefully vetted assigned an inexperienced kid to my motorhome. When they had to remove the heads to replace broken exhaust manifold studs, that was OK, but when they put the engine back together, they assumed that all the small diameter hoses were the same, and connected the heater to the IAC intake and hydrolocked the motor. 2 years and 12,000 miles later, it broke a rod.

The radiator presumably came with a plug in the intake and exit pipes; the truly incompetent mechanic may have left them in. In fact, it probably wouldn't be hard to do a primitive hosepipe flow test on the radiator.

Michael

 

When the radiator was replaced, was the water pump replaced also? I think it may be possible to put one of the water pump gaskets on the wrong way round, and restrict
water flow out of the pump.

Michael

 

Tom, I'm confused by what you're writing. Do you mean that the electric fan comes on, or that the fan clutch on the mechanical fan starts the cooling fan spinning? You see, fan clutches are supposed to continuously spin the fan as long as the engine is turning, but they spin the fan faster when the air flowing over them from the radiator is hotter, and allow the fan to spin slower when the air from the radiator is cooler. Your description sounds as if your fan clutch has failed, so that it doesn't spin the fan faster at hot temperatures, and the only way for temperature to come down is for you to idle at the side of the road, or to drive easily in city traffic.

There is a test for fan clutches. Get some cardboard, and with the engine running try to stop the fan from spinning with the cardboard. If the fan clutch is good, you won't be able to stop it from spinning, but if is bad then you will be able to stop it with the cardboard. Just remember not to use anything harder to try to stop the fan or you'll break blades, and don't try to stop it with your bare hands or you'll lose fingers.

Good luck.
Scott

 

Radiator not big enough to keep the engine cool or partially plugged. If you replaced it, I will bet they put a standard 3 core in instead of a 4 core. My 1984 F250 heavy duty king cab with a 460 did this when I got it. After much head scratching I got the previous owner to admit they had the radiator replaced and when it started having heating issues and the new radiator did not cure it. It was a 3 core instead of an original 4 core. Oh and get rid of the clutch on the fan and get a 7 blade fan.

 

 

Scott I'm talking about the mechanical fan clutch. The fan is turning slower when the engine is running cool. If my memory serves me correctly, my old fan clutch would engage at highway speeds if the engine heats up but the new fan clutch does not seem to engage until you slow down by letting off the gas. The fan clutch will engage at city and idle speeds.

 

Well that's the theory and if it is new and still working right. The clutch fan is a horsepower increaser and an mpg improver. However the numbers are so low as to make it not worth the effort. For the improved and guaranteed cooling, I will give up the minuscule horsepower and mpg, every time.

 

Yes, but some else to consider is that in a class A motorhome, you're sitting almost on top of the engine. It's not quiet when its working hard, and when the fan clutches in it's very noticeable. So if you take the fan clutch away you need a much quieter fan.

Tom, are you saying you've had the water pump and fan clutch changed at the same time as the radiator?

Michael