1989 XJ40 overheating problem

I recently rebuilt the top half of my engine (failed head gasket) and it’s running great … except … I’m now having higher than normal engine temperatures, 2 or 3 bars above the 90 deg (normal) position. In the past the temperature NEVER indicated higher than 1 bar above normal and that was while I was sitting at idle for an extended period of time.

+1 bar = 95C … 203F
+2 bars = 100C … 212F
+3 bars = 105C … 221F
+4 bars = 110C … 230F

It tends to happen at low speeds or at idle so …

  1. Fan shroud and rubber blow-thru flaps are all in excellent condition and working properly.

  2. Recently flushed radiator and filled with fresh 50/50 coolant. Radiator and condenser are free of any external debris.

  3. Replaced coolant temp sensor with new unit… no change. Digital temperature gauge seems to be reading accurately based on temp that thermostat opens.

So this leaves me with the fan clutch or the radiator. The radiator has never been out of the car so I’m thinking of removing it and having it opened up, cleaned and rodded.

Also I’m planning on replacing the fan clutch. When cold it spins around about 90 degs. When hot it spins through about 180 degs. Not sure but this doesn’t seem correct, is there any reliable why to test it? The price for the jaguar replacement fan clutch are ALL over the place, from $50 to $250. Any advice on a quality clutch?

So does anyone have any inputs based on these symptoms ? My fried thinks it could be a clogged catalytic converter ? I still have the originals on the car.

Thermostat maybe? You and I are certainly having our share of issues this year!

Larry’s right. You should probably start with the thermostat since its one of the cheapest and easiest options to address. Did you replace yours when you rebuilt the top end?

The thermostat huh ?

I did replace the thermostat a few months before my rebuild and the car did run just a bit warmer after that. Of course that was around late March when the temperatures were much cooler not the near 100F that we’re experiencing now. So I guess I’ll start my troubleshooting by replacing the thermostat.

Any tips on the fan clutch ?

The fan clutch sounds backwards to me, it should be free-ish when cold and firming up when hot I thought? Not that its any use to you but I have two hanging up in my garage.

Try no t stat,see where the temps run.

Thanks guys …

So I removed the thermostat and went for a test ride…

Of course it took a lot longer for the engine temperature to warm up. It got to 90C and stayed there for a while … YEAH ! Then the temperature kept right on going up … and up … and up … ARGH !! 5 bars above normal … GROAN. So it’s definitely NOT the thermostat.

Because I had the car out on the expressway and the temperature stayed high I’m inclined to believe it’s not the fan clutch either. I believe I read somewhere that above 30 mph the airflow through the radiator provides more cooling than the engine fan. So that would eliminate the fan clutch as a problem.

The only thing that makes sense now is that the radiator isn’t cooling the water like it should.

Oh yes, Since this started going on I’ve been getting a check engine warning on the VCM. Code 4, “Oxygen sensor, system indicates full rich”. Are these problems related ???

Taking the stat out doesn’t help cooling - the water pump has no back pressure so the coolant circulates way too fast and doesn’t stay in the rad long enough to cool down. Result? Car overheats.

Ask me how I know!

If the original catalytic converters are on the car, they might be clogged. But if that’s the case, the fuel mileage would be poor, and there would be some lack of power, too. Since that happens slowly over loong time, if that’s the problem, you may not even realize how much power the car is lacking. Take it to muffler shop, and they can diagnose it quickly, by checking pressure drop across the cat. Happened to me, that’s how I know :slight_smile:

Larry …

Well, since it’s overheating with the thermostat in OR out how would I know if that’s the problem. One thing I love about working on cars (especially old ones) is that I learn something new every day.

OK … I’m asking, how do you know, so tell us your story :smile:

So what temp thermostat did you put in, and what temp was the 'stat you took out? There is a wide range available; Rockauto has them from 167F to 194F. According to the table you provided that 27 degree difference equates to 3 bars on the gauge.

You install a new one. That will tell you if the old one is no good or not and eliminate the possibility that your stat is the problem. A lot less work/more affordable than having to do the other steps you have up your sleeve. :wink:

A long time ago, I had another old English 3-litre straight 6 - this one:

Overheated a bit, so logically (thought I) take out the stat. Seemed to work around town so of course now everything was fixed, drove a thousand miles to California …Steep hills, hot weather, boil boil boil …couldn’t figure out why she got hot, as I’d removed the stat, right?

Wrong. I found out just what I told you, water (that’s what I used back then) doesn’t stay in the rad long enough to get cooled so it just gets hotter and hotter.

AFAIK car ended up as the pace car in a California speedway or demolition derby, not sure which.

Ah, the old Austin Westminster, like most of that era car, built like a tank with a full crossmember chassis,gotta love cars before the dreaded Plastic.

Temp problem, had the same problem on a LS1,new radiator,still hot, changed thermostat to a lower opening temperature, problem solved.

I believe I use an 82 C degree stat in my old crate

Good spot BTW Gordon …

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I have a 1988 XJ40 with the same sort of issue temperature creeps up had to turn on the heater which in Adelaide in summer is not a good idea. I replaced the coolant hose from the heater to the water pump

It seems to be better as the old pipe was swollen but I also played around with the rubber flaps on the radiator surround for stop start traffic

the other thing I did was replace the external electric fan with a lower rated temperature thermal switch on the radiator so the fan kicks in at a lower temperature

Woo-hoo, great photo! Thanks for posting. Please tell what model the car is.

Gordon spotted it, a 50’s Austin Westminster, 3 on the tree with overdrive. Had a nasty habit of the hood trying to fly up when you hit 90mph - which it did once when I was passing someone!

(sorry 'bout the hijack Groove)