Troubleshoot My Vehicle

Recommendations and reviews from 1 person

• Referral from October 3, 2014
  

  Chris M. asked:

  Recently acquired a 1972 Cadillac Fleetwood, it's overheating which could either be the thermostat or the water pump, Anyone in San Francisco recommend a good trustworthy mechanic that works on these old cars?

  

  Jim M. replied:

  had several GM cars from that period... several reacted differently to heat at different speeds... one was worse than the rest. Most of them have a fan clutch that's dual mode... part of it is controlled by centrifugal force. The faster the engine goes, the more the clutch slips. That's so when you're out on the freeway, the fan doesn't need to rotate at the same speed as the engine... because you're getting cooling from wind coming thru the radiator because of your speed. The other is temperature controlled. When that copper spring in front of the fan gets hot, it opens orifices to let fluid (silicone?) into the clutch, which causes it to engage the fan. 72 Cadillac probably has an idiot light for temperature, so you can't tell what the engine temperature is doing, until it's too late. Ultimately what I did to prove the problem was put on a non clutch fan... suddenly the overheating problem was gone... but the fan was on full time, which affects performance and gas mileage... and it's NOISY. Actually, if you're out on the highway, on a hot day, with the a/c on... and the red light comes on... and you didn't hear the fan clutch engage and cause a noise up front that sounds like an 18 wheeler bearing down on you... the fan clutch isn't working properly. Amazing how many dealers I went to that didn't understand any of this. I tried aftermarket fan clutches... most of them only have the centrifugal clutch mechanism, so they didn't help. Finally bit the bullet and paid the big bucks for an OEM GM fan clutch... problem solved. http://troubleshootmyvehicle.com/gm/4.8L-5.3L-6.0L/bad-fan-clutch-troubleshooting-case-study-1

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