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Unread 10-12-2013, 05:14 PM   #1
BuckarooBanzai
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1994 YJ Wrangler 
 
Join Date: Nov 2006
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1994 YJ 2.5L Low Engine Temp and Heater not Hot

Hello, folks!

My 1994 YJ 2.5L has a 195-degree thermostat, but the temperature gauge rises to 165 degrees or so when operating. Also, the air from the heater is warm, but not as hot as it used to be.

The radiator is 2 years old, and the water pump 1 year old. I replaced the thermostat to make sure it is set to open at 195 degrees (like the previous one), but there was no change.

The gauge seems to work because a coolant hose recently developed a crack, and as the engine lost coolant, the gauge displayed higher temperatures.

What causes this and how can I repair it? Winter is mighty cold here, and I would really like to have a working engine and heater.

(Forgive me if this has been answered, but I can't find a thread discussing this.)


Last edited by BuckarooBanzai; 10-12-2013 at 08:30 PM.. Reason: new and improved
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Unread 10-13-2013, 03:29 PM   #2
BuckarooBanzai
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Join Date: Nov 2006
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This is probably the solution, but it seems odd that two thermostats of different brands, purchased months apart in different states, would would cause the engine to operate at 165 degrees.
http://www.jeepforum.com/forum/f12/w...s-cool-503185/
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Unread 10-15-2013, 09:21 AM   #3
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
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There is a bunch of good info on the thread you posted. A few more things to add to it. Air is not your friend. If you had a cracked hose you are allowing air into the system and the pressure to drop causing it to run cooler. Check the integrity of the cooling system with a pressure test. Add a flush T in line with the heater hose from the tstat housing. You need to be able to flush the cooling system and it allows you to burp the air from your cooling system easily. Check the fan clutch cold by spinning the fan and make sure it spins free. You can check the temp sensor to see if it is getting the correct resistance but if the heater is too cool then my bet would be on the things I posted.

The tstat does seem to make the most sense by what you are desribing and I have helped others who have had 3 bad from stock. Post back what you find.
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Unread 10-19-2013, 03:39 PM   #4
BuckarooBanzai
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1994 YJ Wrangler 
 
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Thanks for the response!

The temperature problem began before the hose split, so I don't think air is in the system. Also, I had it flushed since then.

The fan spins freely, so the fan clutch does not appear to be the issue.

This morning I replaced the thermostat again (that's a total of 3 replacements for those of you playing along at home). This thermostat is a different brand and made in a different country that the others. The Jeep still runs at the same temperature (~165 F).

So, this thermostat could also be bad, but why, after replacing the water pump and thermostat last year, does the engine not warm above 165 F with 3 different 195 F thermostats? As you stated, all 3 could be bad, and I could understand each one opening at different temperatures, but it is improbable that all 3 would open at the same incorrect temperature.

Here's hoping the 30-below weather takes its time getting here.

Last edited by BuckarooBanzai; 10-19-2013 at 03:42 PM.. Reason: more clarity, less unclarity
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Unread 10-19-2013, 04:31 PM   #5
Que89YJ
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1989 YJ Wrangler 
 
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Did you burp the air after replacing it. Check the temp guage sensor on the rear of the block. It's a resistance measurement. See if it agrees with the guage.
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Unread 10-20-2013, 02:40 PM   #6
jimbos76cj
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1989 YJ Wrangler 
 
Join Date: Jun 2007
Location: Florida
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Air in your system would not cause it to run colder. I think you may be having 2 seperate issues.

1) Blockage in the heater core. get the engine up to running temp and feel the hoses going into and coming out of the heater core. If one hose is alot hotter then the other you have a blockage in there.

2) Running to cold. I would buy a Cheap mechanical gauge from the parts store and install it to get a really good reading of what temp you are runing at. Or buy a good quality mechanical gauge and permantly intstall it into the jeep since the stocks ones are not the best.

You can tell alot from a vehicles cooling system by feeling the hoses. get it up to that 165 mark and see if all the hoses are the same temp. If one is really hot or cooler compared to the rest then you probably have a blockage.

Oh another cheap and easy way to disgnose it.

find a ac tech.. most will have a laser temp gun or buy a laser temp gun from hrbor frieght or... If you have any friends that work for a Fire department have them use thier TIC to see what temp the block, hose sand radiator are.
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88 YJ 35's 8.8 rear, family style roll bar, ax-15 external slave conversion, Custom double D fab dash 4" of lift taurus fan, Head light wiring upgrade, MSD 6al, JB conversions SYE, 258 with RV cam, Long tube headers, Borla exhaust. 1"mm, Auto meter gauges.
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Unread 10-20-2013, 02:50 PM   #7
Que89YJ
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No the air will cause the sensor to read wrong.
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Unread 10-20-2013, 03:04 PM   #8
jimbos76cj
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Location: Florida
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Im sorry sir.. I miss read you. I thought you meant the air pocket would cause it to physically run colder.. Yes indeed it will cause the sender tobe off.
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88 YJ 35's 8.8 rear, family style roll bar, ax-15 external slave conversion, Custom double D fab dash 4" of lift taurus fan, Head light wiring upgrade, MSD 6al, JB conversions SYE, 258 with RV cam, Long tube headers, Borla exhaust. 1"mm, Auto meter gauges.
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Unread 10-20-2013, 07:05 PM   #9
BuckarooBanzai
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1994 YJ Wrangler 
 
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Well, it was foolish of me to have assumed the temperature sending unit was functioning properly. I replaced it today, and now the gauge fluctuates from ~205'F to ~220'F. I probably allowed air into the line when I replaced the thermostat.

Both heater hoses are ~150'F, and they actually feel hot--I can't hold them for long. Previously they would get hot, but I could hold them indefinitely.

Air from the defroster vents feels hot-ish, but air from the floor vents feels cooler. It's 50 above outside right now, so I don't know how the engine/hose/vent temperatures will translate to the sub-zero weather that is around the corner.

Last edited by BuckarooBanzai; 10-20-2013 at 07:10 PM.. Reason: More understandibility, less anti-understanibility
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Unread 10-20-2013, 10:07 PM   #10
Que89YJ
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1989 YJ Wrangler 
 
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Great news!

"In my experience, nothing is ever what it seems to be, but everything is exactly what it is."
BB quote.
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