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Post by phewop118 on Jul 14, 2018 16:18:26 GMT -6
I haven't driven the 4.0 in the summer in a while since it didn't have A/C. When I'm driving around on local streets (35mph) my coolant temperature seems to run between 220-240. Seems rather high. Revving it or taking the speed up brings it back to 210 or so after a few minutes. Cooling fans both work.
What do you guys usually see for operating temperatures in the summer when driving around town?
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Post by Marc on Jul 14, 2018 18:24:23 GMT -6
On the hottest day that I drove my 2001 4.0, 8/6/2001, in moderate traffic not over 40 mph with the A/C on, the temperature was 110* outside. The needle did not go past the middle mark on the gauge. I think that's 200*.
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Post by phewop118 on Jul 14, 2018 23:01:53 GMT -6
The needle is fluctuating only a little above the middle at peak temperature. However, the middle seems to be around 225, which doesn't seem right (on my 3.5 it is about 205). I know these have thermostats that don't open until 206, but I'm wondering if a missing plastic baffle under the front end could be a factor too.
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Post by Marc on Jul 15, 2018 7:25:50 GMT -6
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tigger
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Post by tigger on Jul 15, 2018 13:48:31 GMT -6
^During an hour in stop and go traffic. FWIW, the middle mark on the gauge is ~200 oF (confirmed by scan tool). And the recommended Tstat is 180 oF. If revving the engine brings your temps back down, your water pump isn't functioning efficiently. Check the belt and tensioner for slippage, but you probably need to replace the pump.
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Post by Marc on Jul 15, 2018 14:25:14 GMT -6
FWIW, the middle mark on the gauge is ~200 oF (confirmed by scan tool). Thanks for that info! I'd been wondering about that for a long time.
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tigger
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Post by tigger on Jul 15, 2018 21:10:18 GMT -6
Thanks for that info! I'd been wondering about that for a long time. No problem Marc. Just a little extra info... Over 100k miles, 12 years, 3 scan tools and 2 water pumps, the scan tool reading has always been between 197-203 degrees. The needle has only been above the middle mark once, when the tensioner pulley disintegrated, haha!
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RCA1186
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Post by RCA1186 on Jul 16, 2018 5:55:30 GMT -6
Yep tigger has it right per usual haha. The Tstat should open at 180, and I too was going to suggest waterpump if revving brings temp down right away. Maybe just the WP belt tensioner. Middle mark is also 200 on the classic but it's marked on the gauge
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Post by Marc on Jul 16, 2018 11:15:38 GMT -6
Middle mark is also 200 on the classic but it's marked on the gauge So then I guess that the bottom mark on the 2G water temp gauge & the top mark on that gauge are the same temp as on the Classic?
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Post by phewop118 on Jul 16, 2018 17:07:55 GMT -6
I double checked alldata... It's saying 188 it will start to open, with full open at 206. Pretty much all of my other GMs are 195 full open.
Also, I went to check coolant and I couldn't get the surge tank cap off (at least without destroying it, which I didn't do) . That's probably a good indication that it is separated. Ordered a new cap. Will see if it helps.
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Post by tigger on Jul 16, 2018 23:09:32 GMT -6
I double checked alldata... It's saying 188 it will start to open, with full open at 206 I don't have AllData, so I looked it up in the FSM, lol! The 188 and 206 you're saying are start to open/fully open coolant temps are actually tempilstik ratings... Tempilstiks are surface temperature indicating crayons. They melt at a prescribed temperature, in this case, 188 and 206. But, they're measuring the surface temp of the outside of the thermostat housing, not the actual coolant temp at the thermostat. They're kind of an old school way to determine if the thermostat is stuck open or closed. A 180 thermostat should begin to open at 180, and be fully open by 190, 195 max. I did find it interesting that the FSM said that normal operating temperature is indicated on the gauge at the middle mark, but the actual temperature could vary from 190 to 220. What?
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RCA1186
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Post by RCA1186 on Jul 17, 2018 6:20:31 GMT -6
Middle mark is also 200 on the classic but it's marked on the gauge So then I guess that the bottom mark on the 2G water temp gauge & the top mark on that gauge are the same temp as on the Classic? Anyone's guess, I'd venture to say "most likely" though Here's a pic of the classic cluster for reference. (not my image, pulled from the internet)
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Post by phewop118 on Jul 19, 2018 7:44:19 GMT -6
I decided to take the 4.0 on my 90 mile drive to work (haven't driven it more than 10 miles at a time in nearly 2 years). Temperature was stable for the first 25 miles right around 200 degrees F. However, after stopping briefly at a tollbooth, it rose to 214 and stayed between 210-218 the rest of the way. The needle remained just below the middle mark the entire time.
I'm going to put the new cap on before driving home this evening to see if it makes any difference. I'm wondering if coolant age could also be a factor... It's probably 5-6 years old.
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Post by Toronado3800 on Jul 19, 2018 8:23:03 GMT -6
I decided to take the 4.0 on my 90 mile drive to work (haven't driven it more than 10 miles at a time in nearly 2 years). Temperature was stable for the first 25 miles right around 200 degrees F. However, after stopping briefly at a tollbooth, it rose to 214 and stayed between 210-218 the rest of the way. The needle remained just below the middle mark the entire time. I'm going to put the new cap on before driving home this evening to see if it makes any difference. I'm wondering if coolant age could also be a factor... It's probably 5-6 years old. 210-218 seems acceptable. My 3.8L 89 Toronado made it to ~280,000 miles (when I traded it in!) and it idled at 212-214 if I remember correctly. Not to say you shouldn't change your fluid, but I think I read these 1G high fans don't even come on until 220ish.
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Post by phewop118 on Jul 19, 2018 21:28:18 GMT -6
Well the coolant cap didn't make a difference, even though it looked rough inside (gasket was pretty much gone). The coolant has a bad smell to it, like it's oxidized... Gonna get it flushed. And change thermostat to 180 degree and see if it helps.
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tigger
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Post by tigger on Jul 19, 2018 22:14:24 GMT -6
I'm wondering if coolant age could also be a factor... It's probably 5-6 years old. Are you still using Dex-Cool, or have you switched to the cheap green stuff? The anti-freeze/coolant properties of either really don't degrade that much over time. But the corrosion protection certainly does... And I'd recommend just doing a drain and fill over a flush. It won't get all of the old out, but it will restore some level of corrosion protection.
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Post by phewop118 on Jul 20, 2018 5:37:04 GMT -6
It's dexcool. Probably 5-6 years old. Maybe newer though (can't remember what year the old waterpump siezed, but it would've been replaced with it).
If I replace the thermostat, should I replace as an assembly? Or just the thermostat itself, not the housing?
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Post by tigger on Jul 20, 2018 17:02:59 GMT -6
If I replace the thermostat, should I replace as an assembly? Or just the thermostat itself, not the housing? I didn't know that was an option, haha! The tstat housing is part of the water pump cover on the 4.0. Seems like pulling the whole cover would be more difficult than just removing 2 flange bolts and pulling the stat...
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Post by phewop118 on Jul 20, 2018 20:59:16 GMT -6
Thanks. Haven't done one on the 4.0. On the 3.5 the thermostat is replaced as part of the water outlet assembly.
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