Page 16 - Summer 2017 GMC Vintage RVing

Technical Corner MAINTENANCE, PARTS, TIPS, INNOVATIONS AND MOREDashboard WarningsDick Paterson | 1976 Eleganza II | 705-325-4554 | Springfield Ignition | springfield-ignition.comIn reply to a question of “What Warnings” from the motor could signal an imminent problem? I began to try to sort through the major signals for the most common causes that would have you “crying on a shoulder”.Reliability is far more dependent on maintenance than on miles travelled. One has to only look at the thousands of highway tractor trailers criss-crossing America on our highways and equate that to how few roadside casualties they have – most are tire related, not mechanical failures. Truck fleet maintenance programs are rigid and are top priority in every major carrier company. By comparison that regimen is often lax or absent for an RV. A casual walk about of your GMC prior toits occasional use can be a recipe for some soft shoulder crying.A maintenance log is extremely important. Document mileage and/or calendar dates with headings for oil changes – chassis lube – hose and fluid level inspections and top offs, plus any repairs. These entries will be catalogued there for your own traveling piece of mind, and as a value added plus, in the event you want to sell.Ignition and/or fuel issues do not usually result in serious engine damage. Expensive damage lurks in the shadow of just two fluids – oil and water.Let’s Do Coolant FirstThe gauge reading may differ from coach to coach, however most owners have a “watch feel” for how their instruments appear as they drive. Reading can differ if gauges have been changed, and/or added. Often added instrumentation is 12 volt powered from the headlight switch to include the ‘dimming’ feature. This source for 12 volts will overwhelm the OEM ground.If your gauges change their reading when you turn on the headlights, adding a heavy ground wire directly to the aluminum plate under the passenger side hood will correct that.The GMC came with dash ‘low level’ warning light for radiator coolant. It is triggered by level content in the system, not temperature. The manual shows its location on the back side of the radiator side tank. A small rubber covered terminal is on the end of a black wire.If it is still there, clean the terminal.Any need to keep adding coolant must be tracked down. There are lots of old hoses and tired clamps throughout the cooling system. Slow leaks are insidious, and annoying. However, if a hose bursts or splits, then severe, overheat and the resulting engine damage takes only moments. Hot coolant under pressure exits a motor in a heartbeat. If caught in time, minimum damage could just be cracked heads. Beyond that, piston rings seize in the bores – pistons collapse – rod bearings follow – call it a meltdown.On the suction side of the water pump any soft collapsing hose restricts coolant flow. The large lower radiator hose has an internal coil spring to prevent collapsing, heater hoses do not. Restricted flow is usually undetected until you boil over. Hoses that are subject to flexing will usually give up at their terminal (point of the hose clamp). Clamps are subject to rust corrosion at their threaded tension bolts. When replacing, “stainless steel” clampsare a good investment.Radiator caps have a service life due to their rubber seal – a 9 lb. rated cap that leaks will not hold coolant or its “rated” pressure. When the pressure falls off, the boiling point for the coolant falls with it. The radiator has the responsibility of rejecting the cooling heat into the air passing through the fins. Additionally with its two internal heat exchangers it acts to bothheat and cool the transmission fluid and the motor oil.Next Subject – OilThe life blood of the motor. Any signal that the pressure has changed – demands instant inspection. Leaks from the hoses that run from the oil filter adapter to the radiator are the killer ones, as they are under full oil pressure and if one goes the motor goes with it. I doubt that there are many GMC’s on the road that have not been upgraded with the “Slaten” stainless hoses (contact information: Classic Coaches & Accessories on page 23). If the coach is new to you, check those hoses out, before you go anywhere.Oil leaks can usually be located and fixed. Unattended they can worsen and become “on the road” worrisome. Valve covers and fuel pump mounts are the most common as are both rubber “fill tube elbows”, intake manifold seals back and front will require some mechanical re- and re-work to fix. (Block off the crossover heat passage when the manifold is off.)Often oil drips from a point on the motor – that is not at the source of the leak making it hard to pinpoint. As the fan air flows over the motor, the oil is moved towards the rear. Park over some newspapers and clean off the motor with a degreaser. Then start it and watch carefully around the front area – dusting suspect areas with talcum powder – helps you find the source easily.The original “PCV” (positive crankcase ventilation) system is a closed system that works very well when the PCV valve is free to function. Anything that restricts its ability to vent, will result in crankcase pressure forcing oil out through seals – back and front.Dipstick readings on ‘unmolested OEM systems’ cannot lie. Thereafter, all bets are off. I have seen some replacement dipstick mods that are truly creative art forms. The manual shows three different “upper” tube lengths hence some confusion. Quantities for oil changes including the filter are same for 403 and16 GMC VINTAGE RVING MAGAZINE | GMCMI.COM