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Old 06-05-2009, 12:20 PM   #1
KTC
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Engine hot spots: questions about thermostat, spark plugs

I get a convulsive shudder from time to time when I shut down my 4 cyl '87 YJ. Also starts slowly, sounds like cylinder's are starting out of synch, whenever I start back up right after the weird shuddering shut down. Starts fine every other time.

Based on info I got in the forums and elsewhere, I'm thinking I have hot spots in the engine.

People have recommended replacing the thermostat and switching to cooler spark plugs. I'm gonna try both.

Questions are: what's the difference between hotter and cooler spark plugs? (yeah, I'm that much of a n00b).

Also, I understand about how the thermostat works, but I keep finding 195║ OEM style thermostats, and 160║ "high performance" thermostats. Other than the fact that they open up at different temps, what's the functional difference between the 160║ and the 195║? Since they're both open continuously above a certain temp (if I understand right), will it really make a difference with my hot spots?

Love my Jeep. Just learning as I go along. Any and all advice appreciated.

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Old 06-05-2009, 01:18 PM   #2
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Check the timing. What condition is the carb in? Original condition? I am unfamiliar with diagnosing the shuttering you have described. Does it backfire?

Cheap thermos fail soon. All thermos will fail. Some are engineered to fail in the open position, leaving you with a motor that warms up poorly and doesn't blow warm air. Or you have a failed thermo in the closed position reulting in overheating and some part of your Jeep needing to be replaced in addition to the thermo.

Robert Shaw is good stuff. But not the only brand worth using. This is a part you should not cheap out on.

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Old 06-05-2009, 01:29 PM   #3
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if by shudder you mean it chugs an extra time or two, i'd be looking at timing. that'll also make it slow to crank when the engine is started hot.

im running a 180 tstat, fwiw
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Old 06-05-2009, 04:28 PM   #4
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How do I check the timing?
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Old 06-06-2009, 06:49 AM   #5
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You should take it to a shop that you trust and ask them to give it a good once over. Then you will know where you stand with timing, fluids, proper operation, etc. If you are not experienced with this type of thing, let an expert look at it before you spin your wheels too much.

Be safe!
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