I'll cut right to the chase
New radiator
New water pump
New fan clutch and fan
New fan switch
180 thermostats
Bled and bled

Still overheating.
Am I missing something. Car is overheating at idle but will not if I'm on the highway. It will creep up above the N if stuck in traffic or slowing down. Please help I don't know what else to do.

Evan
89 Xjs 5.3l

 

Faulty gauge? My next step would be to measure the temperature with an infrared gun.

 

I've just been through the same for the past 3 months but I am now out the other end of it running cool again, so I feel your pain.

Flint makes a good point about the gauge flakeyness, so getting a cheap IR gun from Harbor Freight or similar should be your next step. I usually measure on the hoses right before they go into the radiator on both sides, then measure the bottom hose also. I'm getting around 190 to 195 on the top hoses, and about 3 to 5 degrees less on the bottom hose. I'm running 190deg stats

If you're overheating at idle but not at speed it points towards a fan problem. Is your electric fan coming on ?? If it's not coming on, you can just jump the switch to make it run temporarily and go and sit at a few traffic signals and see if it still overheats.

Did you do this work yourself or someone else ? How did you bleed the car ? I found I had to bleed mine 3 or 4 times every time I opened the cooling system. I use Dougs tried and tested procedure as found elsewhere on this site.

When you drained the system before starting the work was there any debris in there ? Did you add any coolant filters ? (Not saying coolant filters are relevant or needed, it's just an easy way to check if you have crud in your system or not)

Post back and we'll take it from there.

I think gauge/sender or aux fan are in the lead right now for the culprits

 

What is your definition of "overheating" ? And what are the ambient temperatures?

Cheers
DD

 

Sarc and Doug

I did do the work myself, It was a PITA. I bleed the sucker on a hill each time a few little air bubbles came out of the radiator, other than that is was free flowing. The Aux fan does come on when its supposed to. I haven't changed the Temp Sender yet. I'm thinking this is my next step. The gauge is moving above the N while driving with the A/C on , even with the A/C off it still goes above the N. Also, the outside temp is about mid 90.

 

Ok. Get an IR thermometer and let's get your real temp readings.....

 

If it goes a little above the "N" and stays there, it might be as good as it gets.....in 90ºF ambient conditions.

If it keeps climb-climb-climbing, you still have a problem.

In a perfect world every car would have enough cooling system capacity to keep the coolant temp hovering at thermostat temp no matter what the conditions are. In reality, many don't have that kind of capacity....Jag V12s certainly among them....so they run a bit hotter uphills, in hot ambient conditions, etc.

I agree, though, that you should get an i/r thermometer and so you can get a rough idea what the actual temp really is.

Cheers
DD

 

Just a thought is the Aux fan running the right way?

 

IR Thermometer is reading 265 and 270 on the top hoses. today coolant started seeping thru the top left hose. I'm thinking this is very bad. What could be causing this? both fans are working. Pump, stats and radiator are new

 

Wow, that's hot.

More later


Cheers
DD

 

Wow that is very hot.

If you are not overheating at speed but are overheating at idle that would point me towards your cooling fans. More heat is generated at speed which your car has no trouble shedding with sufficient airflow through the radiator. At idle there should be less heat generated, but your fans aren't pushing enough air. Is your advance Lucas or Marelli? A malfunctioning advance system (for the Lucas either the vacuum side or stuck mechanical) will cause extra waste heat at idle, although a well working cooling system should be able to handle it.

You say you replaced the fans and radiator. Check your shrouds are installed correctly and aux fan is blowing in the right direction. Did you install weatherstripping when you replaced your radiator to plug all the areas the air can bypass? Not sure that would make such a dramatic difference, but will help.

Cheers,

- Will

 

Hi Will

I have the Marelli ignition ( not sure of the timing is off or even if it can be adjusted) the crank sensor at the front of the engine is new and Yes, I did replace all the insulation around the radiator. Everything seems to running correctly the aux fan is coming on as needed and shuts off about 5-10 mins after the car is turned off. The fan and clutch are spinning with force. Just the other day it was raining and very cool outside. The temp never went above the N even with the a/c while driving. It's just at idle the car heats up very quickly. And with almost 270 at the hoses I'm worried about the head gasket if It's not already blown. And more ideas?

Thx

 

Yes, very hot. I was panicking at 230.

It's been asked a few times but not confirmed..... is the aux electrical fan running the right way ? It should be sucking air in through the rad, not trying to push air into the rad.

Also there are 2 flaps on the bottom of the radiator shroud, under the aux fan..... they are supposed to be closed when the car is stopped. Are they ? (They need to be closed to force the fans to pull air through the rad and not just pull air in from the engine bay)

Also, can you confirm, did you replace the aux fan also ?? If you replaced it, what did you replace it with ? A standard Jag fan ? or an aftermarket fan ? I'm asking all these questions about fans because I've just been through 3 months of hell because of electric fans. Don't want to derail the thread, but let's just say one black fan that spins isn't necessarily the same as another black fan that spins.

During my 3 months of hell I discussed various "doomsday" scenarios with my indy Jag mechanic. Head gasket failure came up a few times..... If the head gasket is going, apparently it can break into pieces and end up in the cooling system itself, usually blocking the radiator :-(

BUT the thing is cool at speed, which pretty much rules out a flow problem...... I still think you have a fan problem.....

 

are you positive the thermostats are right?? They can fit but be too short/long and not function properly. If they aren't the right length they can fail to let enough coolant to evacuate the block and be cooled, it just gets redirected back into the block.

problem sounds like electric fan. Even if it comes on at the right time could be shot and not spinning at a high enough RPM.

Other than the stats being suspect thats all that sound like you have to worry about. So id check stat length and be sure that fan is running. Jump the fan so its constantly on and see if that brings you down. If it doesn't your fan is either too slow or problem is elsewhere.

also check for blockages in radiator and condenser fins?

 

I'll try changing out the stats. How do I jump the aux fan to run all the time?

 

Check your thermostats to be sure they have the little "jiggle pin" and if they do, be sure it's placed at the top. If they don't have the jiggle pin replace with tstats that do. Many shops and parts stores sell/use tstats that don't have jiggle pins. The jiggle pin permits proper bleeding of the cooling system.

 

To jump the aux fan, first find the 2 wires going down to the switch. On your 89 I think the switch has already been moved to below the water pump at the front of the engine. (If it's still on the left hand side of the radiator, you can just pull the spade connectors off the switch and connect them together easily) There will be 2 wires going to the switch. On my '92 car these wires come out of a loom that runs down the left hand side of the engine bay. Short these 2 wires together. (I strip the insulation off a little bit on each wire, then I place a crocodile clip on the wires where I have stripped the insulation back and it shorts the switch and runs the fan. (You'll need to tape or somehow seal the wires afterwards to prevent them from shorting on their own)

Agree also with Rogers point.... You need the jiggle pins at 12 o'clock to bleed properly

 

Correct the switch is on the front of the waterpump inlet.

 

If they don't have jiggle pins and have trouble sourcing a t-stat that does, you can also drill a small (1/8") hole in the disk about 1/2 radius out from the center.

Cheers,

- Will

 

Ok. Going to try jumping the wires. At this point ill try anything to keep this sucker from overheating. I'm so tired of looking at the temp guage every 5 mins while driving. It's becoming a habit for me. Also, how many speeds does the aux fan have? I'm just hearing one speed. And does the big fan also have different speeds? I'm asking b/c the big seems to also have one speed. It's forcefull but not sure if it should be spinning faster than it is right now.

Thx.