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post #1 of (permalink) Old 05-14-2007, 02:01 PM Thread Starter
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258 heats up at idle

I've got an 88YJ with 258, MC2100, HEI module, E core coil, TFI cap, etc. I've been having problems with the engine heating up but only when at idle. My first guess was the coolant level...checked out good. I replaced the 195 Tstat with a 180. (it actually seems to accelerate and generally run better with the 180.) The engine would be fine until I sit at a light for more than a minute or two, then the temp jumps up to above 210 and the air/fuel gauge reads off scale lean. I havent been able to pin point if the mixture goes lean before or after the temp goes up, seems like its more at the same time. I replaced the water pump last year so I havent really tried blaming that yet. the timing is at 8degrees at idle and seems to curve up fairly accurately from there although I havent made 100% sure of that yet. It is getting fairly hot around here, around 100-110 but the problem happens at night as well when the temp drops to just about 80. I've got an oil leak at the rear main seal i need to take care of so I've been closely monitering the level until I can find time to replace that pig. I've messed with the fuel mixture, leaned/richen it to see what differences that makes and it doesnt seem to do anything. I'm pretty stumped as to what to look at next. Any ideas are welcome. Thank you
Tim

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post #2 of (permalink) Old 05-14-2007, 02:38 PM
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right about here is where i'd start wondering about the water pump, specifically its' output volume at idle revs

not so much pressure, but volume of water it is moving.....

anyhow, maybe you could try upping your idle speed up a few hundred and test it that way

hope my random thoughts do some good

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post #3 of (permalink) Old 05-14-2007, 03:28 PM
 
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Quote:
Originally Posted by USMCYJ View Post
I've got an 88YJ with 258, MC2100, HEI module, E core coil, TFI cap, etc. I've been having problems with the engine heating up but only when at idle. My first guess was the coolant level...checked out good. I replaced the 195 Tstat with a 180. (it actually seems to accelerate and generally run better with the 180.) The engine would be fine until I sit at a light for more than a minute or two, then the temp jumps up to above 210 and the air/fuel gauge reads off scale lean. I havent been able to pin point if the mixture goes lean before or after the temp goes up, seems like its more at the same time. I replaced the water pump last year so I havent really tried blaming that yet. the timing is at 8degrees at idle and seems to curve up fairly accurately from there although I havent made 100% sure of that yet. It is getting fairly hot around here, around 100-110 but the problem happens at night as well when the temp drops to just about 80. I've got an oil leak at the rear main seal i need to take care of so I've been closely monitering the level until I can find time to replace that pig. I've messed with the fuel mixture, leaned/richen it to see what differences that makes and it doesnt seem to do anything. I'm pretty stumped as to what to look at next. Any ideas are welcome. Thank you
Tim

And it idles just fine? Are there some signs it is actually overheating, or might it be worth while to install a mechanical temp gauge to see what's happening for sure? With the rad cap off and it idling, is there a lot of flow of hot water? There should be if its truly that hot.
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post #4 of (permalink) Old 05-14-2007, 07:43 PM
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If you don't have any issues on the fwy then I really doubt it is the t-state or water pump....if you still have the stock fan then my vote is on the fan clutch..

Easy to test....with the engine warmed up and you start to see the temp climb, open the hood..turn off the ign and watch the fan...it should stop almost as quickly as the engine...if it spins for a couple of seconds then it's shot. In some cases you can actually reach down and hold on to it while it's running....

On a side note...it's easy to test your sending unit...
Just remove it...leave the sending wire attached...connect another wire from the body to a good ground on the engine....and then drop that baby into a bot of boiling water....your gauge should show around 212 deg...at sea level...temp goes down as you go up in altitude.

And once you get the temp problem fixed I would suggest putting the 195 t-stat back in.

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post #5 of (permalink) Old 05-14-2007, 10:12 PM
 
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Jeepdawg, the gauge seems to work, but does it work at idle when the air/fuel gauge also goes off norm? I'm wondering if there is some electrical problem at idle. That's why I'd test it with a mechanical temperature gauge. He could test his electrical gauge as you suggest, conclude its good, when really its getting a badly grounded block that acts up when the alternator speed is low and the battery starts showing the voltage change. My thought is completely eliminate the possibility that the problem doesn't actually exist. We sure do all have different ideas. No doubt we'd all find the solution too. Just different paths to get there.
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post #6 of (permalink) Old 05-14-2007, 11:27 PM
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Tim....that is a possibility...but...it would be easy to see that....an electrical problem like that would show up much quicker....basically, the moment you put the engine in idle, you would see the temp go up....in other words, it would follow the engine RPM's.....but, if it takes a long in this case for the temp to creep up....that indicates that the reading is accurate and in fact going up.

Rule #1 of troubleshooting....go for the easy things first. Check the fan clutch.

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post #7 of (permalink) Old 05-14-2007, 11:33 PM
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If the radiator is marginal, or the shroud is, then at idle when there's low air flow it can overheat, without overheating at speed.
Try something - from cold, let it warm up some, shut it off then feel the radiator core. Look for cold areas - the cold areas aren't getting the hot water flowing through them.

Something else to think about - folks go to extremes with shrouds, fans etc - but don't think about "how does the hot air get out?"
Cooling air has to be able to exit as well as enter.
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post #8 of (permalink) Old 05-23-2007, 11:32 PM Thread Starter
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sorry I havent done my part yet, couple deaths in the family...been busy. I am going to take a really good look at the radiator. I replaced the original clutch fan with a flex-a-lite about 3 years ago and it kicks air around like crazy. under the hood is pretty basic so i have a hard time believing the air flow in that direction is restricted. I've got an old winch on the front with that solonoid box on top...haven't relocated it yet. so thats probably part of the problem. From your responses, I think I've narrowed it down to the radiator area. Is it normal to have some corrosion on the fins, looking down through the filler hole? Any remedies for this, short of replacing the radiator?
As far as the fuel/air situation goes...I know that an engine can heat up when its running too lean. I also know that if the engine is heating up, the mixture could lean itself out, but to the point where it kicks off scale??? Not too sure about that. What else could cause air/fuel mixture to lean out after idling for a couple minutes?
Thanks for the replies
Tim

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post #9 of (permalink) Old 05-24-2007, 08:30 AM
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Is the exhaust flowing free?
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post #10 of (permalink) Old 05-24-2007, 09:40 AM
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Sorry about the deaths in your family. My condolences.

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