Overheat??? HELP

WAKETEK516 · 01-19-2007, 10:04 AM

Okay

Jeep starts up fine... warms up perfectly (temp gauge is right at 200-210).

After I'm driving for a few minutes (maybe 10mins) the gauge spikes to the right (close to 260), the "check gauges" light comes on. Then after about 2mins... it drops RIGHT back to 210 as if nothing happens.

It's not gradual either... it literally spikes, then drops back just as fast.

WHAT THE HELL???

There's no sign of overheating either... i don't smell anything, it's not leaking coolant, and its driving PERFECTLY.

**VDoubleUVR6** · 01-19-2007, 10:11 AM

Hmmm thats weird. Either the temp sender is bad and is sending crazy signals to the gauge or something else. I would start off with the temp sender and put a multimeter to it to measure its functionality.

I dont have my service manual with me at work (obviously) but there is a test procedure for those senders.

mpwal099 · 01-19-2007, 10:15 AM

temp sender might be one and the thermostat might be another. Perhaps it is not opening/ losing properly?

WAKETEK516 · 01-19-2007, 10:25 AM

Quote:

Originally Posted by VDoubleUVR6

Hmmm thats weird. Either the temp sender is bad and is sending crazy signals to the gauge or something else. I would start off with the temp sender and put a multimeter to it to measure its functionality.

I dont have my service manual with me at work (obviously) but there is a test procedure for those senders.

If you could tell me what that procedure is when you're home that'd be great!

If it's not the sender, I'll replace the thermostat.

boredcherokee4l · 01-19-2007, 10:28 AM

my jeep did the same thing and it was the thermostat...buy a better thermostat...i got one and it was like $8 dont buy the cheap one...hopefully that works

WAKETEK516 · 01-19-2007, 10:32 AM

Quote:

Originally Posted by boredcherokee4l

my jeep did the same thing and it was the thermostat...buy a better thermostat...i got one and it was like $8 dont buy the cheap one...hopefully that works

Okay cool... thanks!

boredcherokee4l · 01-19-2007, 10:38 AM

no prob...also dont forget to get a thermostat housing gasket...cause you will need to replace it.

**rustywrangler** · 01-19-2007, 10:39 AM

Ditto, spend the extra few bucks. I would still test your sender If I were you.

morepower · 05-12-2007, 10:31 PM

/8/*8*849*69

hennigm4 · 05-13-2007, 07:46 AM

I had two cars do this, u nfortunantly for me it turned out to be the head gasket on both. The coolant had a bubble in it that would alow steam to go past the temp sender unit causing an instant spike to the gauge. Yours could be just a bubble if you recently had the coolant changed. The symptom of a stuck or slow to open thermostat is not instant, you can see it come on within a couple of minutes after driving. I would replace the tehermo with a good one and keep an eye on coolant level. I believe if the temp sending unit is going to fail it will just fail unless you have a lose wire.

Rocky Balbowa · 02-13-2008, 04:20 PM

Keep me posted, my 98 XJ does the same thing. I flushed the system and changed the water pump and ran it without a t-stat and still the same deal. I thought sending unit, but it actually is overheating now! WTF, I'm going crazy. Keep me informed.

MIJEEPGUY · 02-14-2008, 09:51 PM

I had the same problem today. Was on the way to work (35 mile highway drive in 15 degree temp, it's cold in Michigan). I was listening to Howard and the dummy light came on, temp was at about 250. I pulled over and opened the hood, attempted to loosen the radiator cap and there was lots of pressure. So, I sat there for about 5 mins, started engine and checked the temp. It was at about 215. Drove the rest of the way to work (10 miles) with no problem. Drove all the way home with temp never going above 220. Then I picked up the boys from cub scouts, picked up a pizza and on the way home (8-10 miles total), the temp gauge shot up to 250, dummy light came on and as soon as I could look down the gauge went back down to 220. My guess is the temp sender (thanks VDoubleUVR6's), but I will still flush system and replace thermostat. Will keep everyone posted.

BrunoS · 02-14-2008, 10:43 PM

surging temp gauges are usually air pockets in coolant.

try to get the air out by idling parked steeply uphill, heater set to hot and blower on, for maybe 10 minutes. shut it down, park it, get a snack somewhere and come back. restart and drive as normal. that should help.

after that, you could have a sticky thermostat...rule of thumb: buy the expensive, well made one, better quality. don't screw with going cheap on a thermostat. long lesson!

BIG TIP: as for helping warm upquicker, get rid of air pockets, and provide some emergency coolant flow if the thermostat dies closed, drill a 1/8" hole in the outside ring of metal on the FRAME of the thermostat (NOT the "popper valve in the middle". the hole should also be away from the gasket area. this is a very old racers' trick to prevent coolant problems. place the thermostat in the head, with the hole at the top (towards the sky) for proper orientation. stock MOPAR thermostats (including the "performance" ones) come with these holes in the 185 and 195'F temp ratings, around $10 at the dealer. they are quality and are worth it.

if those two things don't fix the temp "surge" then you have a bigger problem....hate to tell you...but that would be head gasket related. since the 4.0 is a cast iron block/head combo, these are pretty immune from most damage except extreme overheating or ancient coolant that was never, ever flushed or changed that is allowing the head gasket to corrode away.

let us know what happens......

MIJEEPGUY · 02-16-2008, 02:20 PM

Well, here's what happened. The fins on the water pump rusted off. We replaced the pump along with adding the "safer" thermostat (fails in the open position), new radiator cap, and since it was off, the serpentine belt was changed too. We also flushed the entire cooling system. Everything works great, well work the $130. Luckily, it appears the head is fine. Thanks for the tip.

subdewd · 03-31-2008, 07:17 PM

How common is it to have the water pump impeller rust away? My son has a neglected 99 sport that is overheating.
He called me for help because he saw coolant on the ground leaking from the radiator tank.
I went and replaced the radiator. I filled the system and after a trip around the block it overheated.
I let it cool down and put more coolant in . Drove it somemore and same thing. I put in a new t stat and the counterman told me to bleed out the air, I did what he described but it wasn't the same way as told here.
It involved warming it up letting it cool down and refilling. It took about 3 gallons total and now it just seems to overflow into the plastic tank.
I noticed the heat blows cold. I assume that can mean 1) clogged core 2) Air in system anythig else?

Also noticed the electric fan wasn't coming on. The outside temp was 60*F.
Question What is the total capacity of an empty system?
Will the electric fan not working cause overheating if the system is full?
Will air in the system keep the fan from coming on?
As I also asked is it common for the impeller to rust away? Is there a way to
check for this?
Thanks for any and all hlp

01-19-2007, 10:39 AM	#8
rustywrangler Got my eye on you..... Join Date: Apr 2005 Location: Syracuse, NY Posts: 18,657 Profile Gallery Classifieds My Jeeps	Ditto, spend the extra few bucks. I would still test your sender If I were you. __________________ http://i131.photobucket.com/albums/p...k_banner-1.gif Congenital Heart Disease is a reality for me, BOTH of my children have it. Please read up and become aware for future generations Lydia Ann-Acquired 08/05/05 Open Heart surgery 08/10/05 Jacob Patrick-Acquired 01/17/08 Open Heart surgery 02/15/08

05-12-2007, 10:31 PM	#9
morepower Registered User Join Date: Aug 2006 Location: , Posts: 4 Profile Gallery Classifieds My Jeeps	/8/884969 Last edited by morepower; 10-07-2009 at 01:06 AM..*

02-14-2008, 10:43 PM	#13
BrunoS Registered User Join Date: Aug 2004 Location: South Bay Los Angeles, CA Posts: 2,538 Profile Gallery Classifieds My Jeeps	surging temp gauges are usually air pockets in coolant. try to get the air out by idling parked steeply uphill, heater set to hot and blower on, for maybe 10 minutes. shut it down, park it, get a snack somewhere and come back. restart and drive as normal. that should help. after that, you could have a sticky thermostat...rule of thumb: buy the expensive, well made one, better quality. don't screw with going cheap on a thermostat. long lesson! BIG TIP: as for helping warm upquicker, get rid of air pockets, and provide some emergency coolant flow if the thermostat dies closed, drill a 1/8" hole in the outside ring of metal on the FRAME of the thermostat (NOT the "popper valve in the middle". the hole should also be away from the gasket area. this is a very old racers' trick to prevent coolant problems. place the thermostat in the head, with the hole at the top (towards the sky) for proper orientation. stock MOPAR thermostats (including the "performance" ones) come with these holes in the 185 and 195'F temp ratings, around $10 at the dealer. they are quality and are worth it. if those two things don't fix the temp "surge" then you have a bigger problem....hate to tell you...but that would be head gasket related. since the 4.0 is a cast iron block/head combo, these are pretty immune from most damage except extreme overheating or ancient coolant that was never, ever flushed or changed that is allowing the head gasket to corrode away. let us know what happens...... __________________ Newly Painted! Emerald Green '96 XJ 4x4 4.0 HO 5-spd 3" Lift + 31" Tires / D35 TracLok / NP231 Drilled out Stock Airbox / Gauge Cluster Upgrade Magnaflow Muffler / High-flo Cat / MSD Coil

05-13-2007, 07:46 AM	#10
hennigm4 Registered User Join Date: May 2007 Location: leesburg va Posts: 91 Profile Gallery Classifieds My Jeeps	I had two cars do this, u nfortunantly for me it turned out to be the head gasket on both. The coolant had a bubble in it that would alow steam to go past the temp sender unit causing an instant spike to the gauge. Yours could be just a bubble if you recently had the coolant changed. The symptom of a stuck or slow to open thermostat is not instant, you can see it come on within a couple of minutes after driving. I would replace the tehermo with a good one and keep an eye on coolant level. I believe if the temp sending unit is going to fail it will just fail unless you have a lose wire.

03-31-2008, 07:17 PM	#15
subdewd Registered User Join Date: Nov 2005 Posts: 2 Profile Gallery Classifieds My Jeeps	How common is it to have the water pump impeller rust away? My son has a neglected 99 sport that is overheating. He called me for help because he saw coolant on the ground leaking from the radiator tank. I went and replaced the radiator. I filled the system and after a trip around the block it overheated. I let it cool down and put more coolant in . Drove it somemore and same thing. I put in a new t stat and the counterman told me to bleed out the air, I did what he described but it wasn't the same way as told here. It involved warming it up letting it cool down and refilling. It took about 3 gallons total and now it just seems to overflow into the plastic tank. I noticed the heat blows cold. I assume that can mean 1) clogged core 2) Air in system anythig else? Also noticed the electric fan wasn't coming on. The outside temp was 60*F. Question What is the total capacity of an empty system? Will the electric fan not working cause overheating if the system is full? Will air in the system keep the fan from coming on? As I also asked is it common for the impeller to rust away? Is there a way to check for this? Thanks for any and all hlp