What range should vacuum be at Idle? My new gauge is cool, just dont know what
it is telling me yet.
Ron and Julie
73 Painted Desert
> Dave;
> What a sneaky wonderful idea. I believe I used to use a MBZ 12 volt timed
> relay, but an idiot light temp switch would be cheaper and better. The only
> problem would be where to put it.
> Speaking of Temp switches, I replaced my original temp sender with the
> GMCnet recommended NAPA Unit. My cold engine now reads 1/4 hot, and my hot
> engine read 7/8's. I installed a bulb type temp gauge in the hole, and found
> that when my old sender reads 1/4 hot, the engine is at 192 degrees
> (approx.). Also, when I turn on my headlights, my new temp sender reads 1/8
> hotter. I traced that down to the dash lights. Sounds like I have a poor
> ground. I'm going to reinstall my old unit, together with my bulb temp gauge.
> Has anyone else seen the new Napa read too hot, and the original read
> correctly?
> On the vac advance. I read the book (oops) and checked out my 1977 NonCA
> 403. Below 217-223 Degrees the vacuum to the vac advance is ported, and
> should be below 5 inches Hg at idle, above idle, and also underload, the vac
> to the advance should increase up to 25 in Hg. I believe full vac advance is
> above 7 in Hg, at least mine tested out that way. This means that at normal
> temp, no advance at idle, full vac advance almost all the rest of the time.
> Above 217-223 Degrees, the vacuum is routed to the manifold, so the vac
> advance will be under full advance at idle and load.
> The stated reason for retarding the timing below 217-223 was to limit
> emissions. When the engine got hotter than that the "Distributor Thermal
> Vacuum Switch" would advance the timing allowing the engine to cool itself.
> If there's interest in this vac advance setup I can post the original GMC
> pages on my website.
> Happy Camping;
> Mark A
it is telling me yet.
Ron and Julie
73 Painted Desert
> Dave;
> What a sneaky wonderful idea. I believe I used to use a MBZ 12 volt timed
> relay, but an idiot light temp switch would be cheaper and better. The only
> problem would be where to put it.
> Speaking of Temp switches, I replaced my original temp sender with the
> GMCnet recommended NAPA Unit. My cold engine now reads 1/4 hot, and my hot
> engine read 7/8's. I installed a bulb type temp gauge in the hole, and found
> that when my old sender reads 1/4 hot, the engine is at 192 degrees
> (approx.). Also, when I turn on my headlights, my new temp sender reads 1/8
> hotter. I traced that down to the dash lights. Sounds like I have a poor
> ground. I'm going to reinstall my old unit, together with my bulb temp gauge.
> Has anyone else seen the new Napa read too hot, and the original read
> correctly?
> On the vac advance. I read the book (oops) and checked out my 1977 NonCA
> 403. Below 217-223 Degrees the vacuum to the vac advance is ported, and
> should be below 5 inches Hg at idle, above idle, and also underload, the vac
> to the advance should increase up to 25 in Hg. I believe full vac advance is
> above 7 in Hg, at least mine tested out that way. This means that at normal
> temp, no advance at idle, full vac advance almost all the rest of the time.
> Above 217-223 Degrees, the vacuum is routed to the manifold, so the vac
> advance will be under full advance at idle and load.
> The stated reason for retarding the timing below 217-223 was to limit
> emissions. When the engine got hotter than that the "Distributor Thermal
> Vacuum Switch" would advance the timing allowing the engine to cool itself.
> If there's interest in this vac advance setup I can post the original GMC
> pages on my website.
> Happy Camping;
> Mark A
