Chevrolet Repair: Overheating problem 454 Chevrolet engine, head gasket problems, 454 chev

Question
Mr. Adams

I have a 1988 Bounder Class A Motorhome with a 454 Chev Engine, 7.1 liter.It is 35 ft long with auto, power steering, power brakes, air conditioning.

I had problems with it overheating so I had a mechanic look it over and he replaced the following:
1.)Thermostat
2.)Refurbished Radiator
3.)New fan clutch
4.)New Radiator shroud(old one was badly worn)
5.)He wired both the fans attached to the radiator to a common on/off switch on the dashboard so that I can turn the fans on and off manually.

My problem is that the engine still overheats(goes up near the red mark) whenever I climb a medium hill with the fans turned on.

There are no leaks in the radiator, the coolant level is Ok.  No evidence of head gasket problems.

I have talked to my mechanic and he doesn't seem to know what the problem would be.  

My questions:

1.)What could be the problem?  What things should I have checked.

2.)What is the way the radiator cooling fans(2) attached to the front of the radiator are supposed to work?
I know that they each have thermostats, the upper one works off the temperature of the coolant, and the lower one works off of the temperature of the air conditioner.  (I have disabled the air conditioner, belt has been removed, etc.)  How are these fans supposted to work?  Do they have variable speeds so that when the thermostats kick in the fans, do the fans first start slowly and as the heat of the engine goes up they start going around faster?  Or do they just run at one set speed.  The reason I am asking is that when I first purchased this motorhome about a year ago, when the engine started to get hot I could hear a very loud fan noise from the fans evidently indicating they were going around very fast. The engine did get cooler quite quickly while the fans were running, but they ran only intermittently.  The person I bought the motorhome from said the noise was from the fan(s), and was normal.

3.)Which leads me to my next question.  Since my mechanic rewired the fans to operate manually I have not heard the loud fan noise anymore.  By rewiring these fans to a manual switch did that defeat or inhibit the running of the fans at high speed?  When I look at the fans running while the switch is turned on for the fans they are going around but not nearly as noisy or as fast as they used to.  Do I need to reverse that wiring?  How do you test those fans to see if they are running properly?

Please excuse this long question, but I am planning a 1,000 mile trip with this motorhome soon and need an answer as to what the problem is so that I can have it fixed.

Thank you for your prompt answer.

Roger Monson
tkfive@verizon.net  

Answer
The cooling fans are to be mounted between the engine and the radiator (the inside of the radiator). If they are mounted in front of the radiator (on the outside), they are pulling heat from the engine compartment out to the outside which would be backwards. Ultmately causing a overheating problem.
If they are found to be mounted correctly, then you can check both fans by unplugging them at the connection at the fan. There should only be 2 connections, one black (ground) and one red (power).
What you should do is unplug the fans and test the motor for resistance using an ohm meter. Once this number is found, go to a parts store and test the new motor. If you see a dramatic difference, you have found your problem. If you do not see a difference, I would check around for a 3 core radiator.(Radiator with 3 rows inside).
To answer your questions on the fans job:
Imagine when you first start your car, all the coolant is cold. The heat your engine is generating is being cooled by coolant that is trapped in the motor until your thermostat opens and lets it flow into the radiator. When the thermostat closes, it stops the flow again allowing the coolant in the radiator to be cooled down until the thermostat opens again. The coolant in the radiator is cooled by the fans on the radiator while waiting to flow back to the motor.
A lot of times the thermostat will "stick" either open or closed, neither of which is good. A stuck open thermostat causes an engine to overheat at higher or more demanding speeds and loads. the thermostat can be checked simply by watching the small tubes in the radiator for flow upon starting the motor and waiting for the thermostat to open which takes 3 to 5 minutes generally.
The other main cause of overheating, besides the cooling fans and thermostat is, even though you can see the coolant flowing by looking in the radiator, it may not be flowing in the lower half of the radiator from sediments (dirt from age)or additives (like stop leak). This can be fixed by having the radiator cored out (reaming the small tubes) at a radiator repair shop.
Rewiring the fans is not a good way to take a 1,000 mile trip. It is excellent for a quick fix, but is in no way permanant. It will cause the fans themselves to overwork, get hot and eventually after slowing down, quit working all together.
Good luck on your 1,000 mile trip.
If you come by way of Knoxville swing by, it would be good to meet new people.