Did I need to let my 1970 AMC Rambler “relax” before shutting off?

amc
rambler

#1

Back in '72, two friends and I drove across America and back, starting in Upstate NY. The vehicle was a '68 Rambler American. After drives of 3-4 hours and more, the owner of said vehicle insisted we idle the car for 5 minutes or so, to allow it to relax (for lack of a better term), similar to a distance runner. The other two is thought he was nuts!! Comments???


#2

All this time and you have not figured out that the owner was wrong .


#3

What the owner was doing was avoiding what was known as “heat soak.” After a long highway drive in the old days without overdrive or lockup torque convertors, if you left the highway and pulled into a stop, all that heat from the engine and transmission would take a bit of time to cool down at idle with the engine fan running. That prevented the coolant from boiling over if you just shut off the engine immediately and prevented vapor lock on re-start.

My current 2014 Audi has an electric water pump and electric cooling fans that can run after key-off to prevent that exact scenario.

So it wasn’t to “relax” the car so much as prevent it from re-starting or boiling over.


#4

The other big change that has pretty much eliminated vapor lock/fuel boiling is fuel injection. Gas under pressure has much less tendency to boil than gas sitting in a carb or fuel line at atmospheric pressure.


#5

Back in the day it was my guess that the difficulty in restarting many 6 cylinder engines was the likelihood that the exhaust had heated the carburetor and boiled the fuel flooding the intake. Slant 6 Dodge and Plymouth engines were notorious for that problem. After a several miles at high speed the slant 6 would run rough and hesitate when when stopped and idling and shifting to neutral and raising the idle speed was sometimes needed to prevent stalling which would result in a very difficult restart. If the heat riser was sticking and failing to fully open the problem would be more than most people would continue to deal with. Heat riser valves were an occasional problem on the Car Talk forum long ago.


#6

One more issue back in those days was that oil was not as good, it would break down at lower temperature than oil today. After a long run at freeway speeds back then the oil would get very hot. On top of that, when you shut down, some oil would be trapped in the engine, mostly as a thin film of oil coating the inside of the block, top of the heads and in parts like lifters rocker arms and bearings during the heat soak that occurs after shut down.

There were two ways to minimize the damage to the oil, and the subsequent wear on the engine during restart. One was a three minute cool down at idle. My choice always was to slow down to about 60 for the last couple of miles before the off ramp. That would drop the oil temperature and head temperature enough.

That was only necessary if you were going to shut down the engine immediately after exiting the freeway. If you were going to travel a few miles on surface streets or you had only done a short run on the freeway, it didn’t need that cooling off period.


#7

I remember maybe it was Canada, a high speed stretch of road, pulled in for gas, stopped and 71 nova started Showing high temp. Attendant said you can not believe how many cars overheat here when stopping for gas.


#8

Back in the 60’s my neighbor had a Valiant and whenever he’d come home he’d sit on the driveway running the engine at a fast idle for a few minutes. It was right next to my bedroom window so I always knew when he came home. Never understood why he did it and just chalked it up to an obsession. He never failed though. I just thought he was charging up the battery. Then one night he rolled it over but still continued running the thing when he got home, roof dents and all.


#9

Back in the '70s, I worked with a guy who did the same thing with his car. When I asked him why he did that, he stated that it was to “fill the carburetor’s float bowl in order to make it easier to re-start”.
:face_with_raised_eyebrow:


#10

I never head of this particular theory, but years ago I noticed folks sometimes would gun the engine a little just before shutting it off. The purpose I think was to make re-starting easier. Don’t know why that would work, and I never had to do that on any of my cars, they’d start ok w/out doing that.


#11

That was common among drivers of British sports cars of the 50’s and 60’s. It was supposed to make restarting easier but I don’t know why it would either.


#12

My understanding was it would leave some additional gas in the cylinder if the engine was shut down while pushing the accelerator. Friend with old Beetles does that. But I also read that it does a good job of diluting the oil in the cylinder, wearing out the engine faster. Who knows if either is true…


#13

I never heard that one. I owned and drove 4 British sports cars from early to mid 1960s vintage. All twin SU carbs. Never had starting problems.


#14

The 68 mgc-gt 6 cyl always had starting problems, timing slip the biggest issue. Lucky you!


#15

Must have lived in a dry climate! Lucas, the Prince of Darkness, doesn’t like wet weather! :wink:


#16

All of mine were inline 4s. A girlfriend had a MGB GT. A buddy had a 1966 Midget that he started normally and shut off after about 30 seconds. It was then a crank no start. It had fuel but no spark. When I removed the distributer cap the problem was obvious. The fiber rubbing block on the ignition points had fallen off. I had never seen that one before. I have had unusually good luck with used and new vehicles so far. Lucky me!


#17

3 out of 4 were purchased and driven in Western Oregon. Hardly a dry climate. Fortunately rain and no road salt does not cause more than minor surface rust. Vehicles driven in water at the beach then not power washed will suffer rust damage. The 1962 MGA coupe was purchased in Southern California and sold 6 months later when I moved back to Oregon. I had a headlight burn out in my 1966 MGB. As usual I replaced both. The only electrical problem with all 4 British sports cars. I have English blood from both Grandmothers. Perhaps Sir Joseph Lukas Prince of Darkness is a distant relative and I have received family consideration. Or I am simply lucky.