First let me say that 200-202ºF, in and of itself, is neither harmful nor "overheating".

If you're running about 200ºF, the temp doesn't climb-climb-climb endlessly higher, and are confident the you have good *flow* through both cylinder heads, I'm not entirely sure you have a problem with respect to actual temperature.

However, your cooler at idle, hotter when driving scenario suggests, to me at least, that you need to bleed the system again....as that sort of fluctuation is a typical symptom of air in the system. Sometimes it takes 2-3-4 efforts to get all the air out. My own experience is that, based on nothing more identifiable than luck of the draw, is that the fates allow either success at the first try or they will torture you ....making you repeat the bleed procedure a couple more times.

I have the same experience bleeding brakes, by the way :-)

Anyhow, no air in the system is essential to the "good flow through both heads" mentioned above, and good flow through the heads is more important than keeping the temp below 200ºF







I would, too


Cheers
DD

 

Hi Doug

Thanks for the feedback. I replaced the stats, refilled and bled the system..... one of those actions seems to have made the difference. I now have the gauge reading a little past 12 o'clock at idle/in traffic but when I get out on the freeway, the gauge moves nicely to the left again. Now all I have to do is stop the transmission fluid leak from the hoses on the right hand side of the rad and we'll be back on the road !!

I dry fitted those hoses, but should I use some type of thread sealer ? (I used to use Loctite "something" on previous cars)

 

Thanks all for the info. However, do the fan clutch mentioned have any
effect on blowing heat or air condition into the cabin when engaged? I have no problems in my 98 XJ8 with engine temperture just blower for heat and air.

 

@frankly

No, the fan with the fan clutch just keeps the engine cool. The blowing of air inside the car is done by 2 blowers, one on either side of the car

@Doug

I went for another run and drive through traffic. The temp started creeping up again. I got up to 210~212 measured by IR on the top hoses, and at that time the temp on the bottom hose was almost the same. I think I have no or low flow, which can only be the water pump. I'll get that changed. I give in :-(

 

Very good idea, Sarc. I am a great believer in renewing as much as possible within the available budget. First the problem gets solved, second the system then works well for the next 10 years!

I assume that your second electric fan is going full blast while the temp is not dropping? If it is, pump flow would seem to be the problem as long as the thermostats ARE opening fully and the bypass tube IS being closed off properly each side by them when they open.

202° F is 94°C, so I think the bottom hose should be well below this if all is well. Certainly is on my car.

Greg

 

ive got a good water pump for sale!

 

So, some progress over the past few nights. The drive is a lake of coolant and there are dead pets littering the street, but anyway, on to the important stuff......

I did a few tests and mods :

1) Using an anemometer, I measured the wind speed of both of the electric fans as I had them, then I ran a wire straight from the battery to the fans and remeasured. The conclusion was they were pulling about twice the amount of air when connected to the battery compared to my original set up. Lesson learned --> Thin wire does not flow the same amount of current as fat wire. Follow the instructions you were given with the fans and connect them directly to a battery feed (through the supplied switching relay) . Just FYI I have a degree in electronics..... sometimes we are the worst people to actually wire stuff up :-)

2) I ran the car for a while and found I had no heat, which I took as a sure sign I had not bled the system properly.

I rewired the fans, re-bled the system and went for a run. I have heat back again, and so far I seem to be holding temperature....... I'll venture a bit further a field at the weekend and report back.....

(only joking about the pets..... If I harmed any of the pets, myself and the XJS would be forcibly ejected from our respective house and garage with no parole or chance of appeal)

 

Awesome!!! im glad to hear its working so far. Lets hope for goodnews this weekend

 

Just curious, did you also put in a new water pump as you mentioned you might?

Where did you end up connecting the fans to a battery feed?

Good luck this weekend.

 

@Noah

Nope, I'm on the same water pump. I think the biggest issue could have been bad bleeding...... I've bled the car probably 10 times by now, and the performance after the bleeding seems to be pretty varied (as Doug suggested) even though I followed exactly the same procedure every time. Sometimes I had heat, but no engine cooling. Other times I had no heat, funny gurgling noises coming from the bulkhead somewhere (sounded like someone going to the toilet), and no cooling. Other times I had heat but no engine cooling, and finally I seem to have all of the planets aligned.

I connected the fans into the feed wire to the starter motor. The starter motor relay is on the right hand side of the engine bay so was easy to access and splice into. This is a nice big thick juicy cable that comes directly off the right hand terminal post and can no doubt supply plenty of amps. The fans are both individually fused and controlled through relays, so hopefully I don't fry myself. An interesting point I noticed was that when the fans were pulling more amps and producing more air flow, they were actually quieter....... which seems counter-intuitive, but I'm sure there's some resonance or harmonics involved in this somewhere.

 

Some report that 'tis the heater core where air pockets like to reside and install one of those "flushing tees" into a heater hose so as to allow a place to burp the system near the heater.

<shrug>


I've never had that problem myself and had forgotten all about the flushig tee trick until you mentioned gurgling noises at the bulkhead.

Cheers
DD