Topic: XJ running hotter than usual (Read 7592 times)

Brynjaminjones · « **on:** February 09, 2015, 02:45:33 PM »

I've noticed lately that the XJ is running hotter than usual.

It's been running above the 100 degree mark in traffic and at low speeds for a while now which it never used to, but I think that's just due to everything being a bit old and dirty. Above 40ish it's been fine.

Anyway, recently I had quite a hard high speed drive where I was at full throttle for quite a bit longer than usual, and it went a full notch above 100 degrees and wouldn't go back down no matter how I drove afterwards. The next day I had lost a bit of coolant.

This weekend I then had another hard(ish) drive, for about an hour at 90+ mph, and it was running hotter than usual again.

I've got to take it on a fairly decent road trip in a couple of weeks, so I want to make sure this isn't an issue. Any idea what would be causing it to get hotter than usual at high speeds?

One theory I had is that when pushing it hard, my heater core bypass could be leaking, introducing air into the system and also causing the slight coolant loss. Could there be anything to that?

wildwood · « **Reply #1 on:** February 09, 2015, 04:01:05 PM »

Yes check for leaks and rad cap and bypass hose and also.......if it's been dunked in a lot of mud, and is the original......

That poor rad is on borrowed time

bgbazz · « **Reply #2 on:** February 09, 2015, 04:33:57 PM »

....sounds suspiciously like an airflow problem to me. Air nozzle blowing from engine bay outwards to the front can help....I do this on the Nissan every few months and it's amazing how much crap comes out!!

Also, if you have an aircon system that isn't working or needed, get rid of that big thingy (condensor) that sits in front of the radiator...that will make a difference.

gazjeep · « **Reply #3 on:** February 09, 2015, 07:37:00 PM »

I'm with the hippy & Baz on this young fella, did you properly remove all of the Breakout crap from the rad that Jay made you & Sarah go thru, & I mean properly he said in a sagely waggy finger kinds way

Brynjaminjones · « **Reply #4 on:** February 09, 2015, 07:51:34 PM »

Cheers guys - I did clean the radiator as thoroughly as possible after that misleading pair made me go where I shouldn't, and it's been pretty much fine ever since, apart from maybe slightly hotter than before in town.

This heat at speed though is completely new, which is what has lead me to believe that it must be to do with my heater core bypass, as that's the only thing in the system that has changed, unless something has given.

bgbazz · « **Reply #5 on:** February 09, 2015, 08:02:40 PM »

Don't forget that you've been out playing in the snow and slush recently...and that stuff isn't as pure as you might think!

That bypass 'system' you fitted may be adding to the problem, but might also come down to your recent change in driving speed...90+mph for an hour is going to bring out any little abnormalities and get your attention.

I'm sticking with restricted airflow, for the moment.

donk498 · « **Reply #6 on:** February 09, 2015, 08:42:02 PM »

Its ruined you should give it to me to modify!

jay140285 · « **Reply #7 on:** February 09, 2015, 08:59:23 PM »

Did you take rad off when you cleaned it? Mine was off twice and second time still mud came out.

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Brynjaminjones · « **Reply #8 on:** February 10, 2015, 12:51:15 PM »

Quote from: donk498 on February 09, 2015, 08:42:02 PM

Its ruined you should give it to me to modify!

Nice try! I think I'd sell an arm before I got rid of my XJ...

Jay, nope, never took it out, which I think is related to my low speed issues, but these high speed issues are definitely new.

GMad · « **Reply #9 on:** February 10, 2015, 01:02:52 PM »

I had very similar problems with my Grand, which I only actually managed to cure recently.
The first problem was the radiator cap. It didn't actually leak but was rated at the wrong pressure and when the engine got very hot (off road), it pressurised the system too much, blew the overflow pipe off and spat a load of coolant out.
Replacing the cap with one rated to the right pressure, cured the overheating, but then I started loosing coolant. Not much and not enough to leave a big puddle underneath, but I was loosing coolant.
It turns out the the increased pressure caused by the wrong radiator cap, had actually buggered the water pump! Now that I've replaced that, it keeps cool and doesn't leak anymore

Bandit · « **Reply #10 on:** February 10, 2015, 08:15:10 PM »

If crud has been involved it maybe worth checking the bi metal coil in the middle of the viscose fan clutch, had that meself, was so much crud around it it stopped the clutch engaging.

Brynjaminjones · « **Reply #11 on:** February 11, 2015, 11:13:39 AM »

Now that seems worth a look (for the low speed temp) - did you have to remove it to sort it?

jay140285 · « **Reply #12 on:** February 11, 2015, 11:31:47 AM »

Mate don't rule out the Rad for the higher speed temperature.

When mine was running to hot and had to remove the radiator it was on the motorway!

Brynjaminjones · « **Reply #13 on:** February 11, 2015, 11:39:37 AM »

Cheers Jay, I've definitely not ruled it out at all, I just think that the high-speed hot running is a new problem on top of the probably clogged radiator! Since getting it that muddy I've kind of become accustomed to when it runs hot, and this definitely seems to be a new thing, plus the coolant loss hints at something else!

Bandit · « **Reply #14 on:** February 11, 2015, 12:41:13 PM »

Quote from: Brynjaminjones on February 11, 2015, 11:13:39 AM

Now that seems worth a look (for the low speed temp) - did you have to remove it to sort it?

Yes took fan off, i was given another which i used but cleaned mine and is now good, i would defo do as Jay advised, take rad off and clean properly, inside and out, yur heater bypass wont help as the matrix helps with cooling, thas probably whats highlighted yur problem

Hillbilly · « **Reply #15 on:** February 11, 2015, 02:12:13 PM »

Bryn. Is the viscous fan actually working? The Grand has a fan relay tucked away on the inner front wing. I didn't know it was there until mine started overheating and found that was fubared. Just a thought!

Brynjaminjones · « **Reply #16 on:** February 11, 2015, 02:35:36 PM »

Cheers guys, will have a look at the viscous fan and one day will take the rad out!

I think the fan is at least working sometimes, as it very definitely roars when you first pull away after start up. Does that necessarily mean it's still working once it warms up though?

JamesH · « **Reply #17 on:** February 11, 2015, 05:41:12 PM »

Taking the radiator off really isn't that bad a job. It looks quite dramatic when taken apart but a good soak and hosepipe wash and it will make a big difference. You can then rule it out as causing the problems.

Driving at 90 for any length of time in a 17 year old XJ is bound to test it a bit.

bgbazz · « **Reply #18 on:** February 11, 2015, 05:51:49 PM »

Quote from: JamesH on February 11, 2015, 05:41:12 PM

Taking the radiator off really isn't that bad a job. It looks quite dramatic when taken apart but a good soak and hosepipe wash and it will make a big difference. You can then rule it out as causing the problems.

Driving at 90 for any length of time in a 17 year old XJ is bound to test it a bit.

Especially when you have reduced the amount of coolant by a significant amount.

Bandit · « **Reply #19 on:** February 11, 2015, 05:52:15 PM »

The xj fan is mechanical, it should roar from cold then freewheel after a short while, heat from the rad causes the bimetal coil to move and engage the clutch inside it, mine was packed with mud and the coil strip couldnt move, once washed out i checked it using a hot air gun

bgbazz · « **Reply #20 on:** February 11, 2015, 05:58:21 PM »

At any speed over about 55mph, the fan isn't doing anything...normal airflow, caused by your forward speed, will cool the fluid in the radiator...if that air can get through the vanes.

At lower speeds the fan will be quite efficient (ie. doing it's job), but again, only if air can be drawn through the vanes.

Brynjaminjones · « **Reply #21 on:** February 12, 2015, 01:08:05 PM »

Cheers for all the advice guys. I think I've got it sorted in my head now - I'm going for the following:

Low speed heat caused by old radiator and possibly viscous fan not fully engaging (must investigate)
High speed heat was just about coping with dirty radiator, but now seems to have been highlighted by heater core bypass (loss of coolant capacity as well as slight leak from bypass under pressure).

Hopefully the heater core should be fixed in a week or so, then I'll move on to other issues!

bgbazz · « **Reply #22 on:** February 12, 2015, 02:40:14 PM »

I would attend to the radiator first...it's a piece of cake to do and you can look at the fan while the radiator is out, so you will kill two birds with one stone.

The heater matrix will be a fidddly bugger of a thing to do...and time consuming! Do the easy job first...in my mind, it's preferable to have a motor running at the correct temp, as against a toasted driver!

Brynjaminjones · « **Reply #23 on:** February 12, 2015, 02:53:33 PM »

Though you make a good point, the temperature isn't actually enough to be an issue at all - I'm just aware that it's higher than it used to be. It's still well within acceptable limits.

I'm being moaned at already about the car being too cold, so I'm fixing the heater first to prevent being too much complaining when we head on a road trip in a few weeks!

bgbazz · « **Reply #24 on:** February 12, 2015, 03:03:18 PM »

OK, your car, your choice.

Author Topic: XJ running hotter than usual (Read 7592 times)

donk498

jay140285

GMad

Bandit

jay140285

Bandit

Bandit