I know, not another overheating thread. FWIW, I have read the other threads and while helpful and insightful, have not seemed to solve my problem.

The temp is getting too hot (110-120 C) after a short drive in cool Idaho weather. After some checking on the forum, I went with replacing the thermostat which was my first instinct. New thermostat didn't seem to help much, so on to the radiator.

Today I drained the radiator and flushed it out with a hose. Then added chemical and flushed it some more. A few chunks of build up, but not too bad. Radiator seems to flow good when I flush water through it.

At this point I think it could be the water pump or the coolant temp sensor. It is also possible the new thermostat is bad, so I was thinking of removing it and checking it. I don't have a thermometer, but by touch it is pretty hot. The bypass hose is also very hot.

The fan clutch appears to be working properly, the fan spins right up when the engine is revved.

At this point I think it could be the water pump or the coolant temp sensor. It is also possible the new thermostat is bad, so I was thinking of removing it and checking it. I am pretty sure it is not just a bad gauge. I don't have a external thermometer, but by touch it is pretty hot. The bypass hose is also very hot.

My experience with water pumps is that the weep or leak when they fail and there are no leaks. Is there a way to check the water pump? I need to do some more reading in my manual about how the temp sensor and sending unit work.

Is it possible that there is just an air bubble or blockage in the block? Any other suggestions?

 

Short drive at highway speeds. Or short drive in traffic?




I'd get it professionally cleaned....but even lacking that you should remove it to clean the build up of debris between the condenser and the radiator. I can all but promise you'll find quite a mess. I've seen some where 25-30% of the radiator was clogged with external debris





Not a terribly convincing endorsement :-)

Let the engine get up to about 95-100ºC, turn it off, and give the fan a spin with your hand. Does it spin more tahn 1/2-3/4 revolution? It shouldn't.



Blockage, maybe, yes. Air bubble? This engine isn't prone to air pcokets and you didn't mention the temp gauge going up-n-down, which is a fairly common sign of air pockets.

Nothing unique about this cooling system. Good thermo, clean radiator, good fan clutch is about all there is to it.

Cheers
DD

 

Short drive at highway speeds.

I boiled the thermo just to be sure and it opened. I am warming the engine right now so I can check the fan clutch at operating temp.

I know the aux electric fan is not kicking on. I ran a jumper and the motor works so I'll have to check the wiring fuse and relay. Would the engine get to hot without the aux fan?

I figured I would pull the radiator and have it cleaned, I just wanted to check if it was plugged bad.

Thanks for the help.

 

you don't mention the automatic, auxiliary cooling fan, is it coming on?

 

My money is on a clogged radiator




That little fan DOES make a difference in traffic driving but I wouldn't expect it to help much a highway speeds.

This might help you in checking the circuits:
Aux Electric Cooling Fan Checklist, Series III

Cheers
DD

 

the auxiliary fan comes ON at a pre-set coolant temperature, the thermal switch for the aux. fan is mounted at the bottom right side of the radiator. Yes, the engine will get hotter without the aux. fan running, and it also keeps running even after you turn the engine off and a few minutes later shuts down by itself.

 

I agree with clogged radiator. I had mine rodded recently and the guy said it was ~30% full of crap. Operating temps dropped 10 degrees.

I didn't see it mentioned, but please confirm that you are or are not losing any coolant.

Good luck,

Eric

 

My money is also on a clogged radiator. Mine seemed OK but engine still overheated, (in the 1990s) but a re-core cured the problem. These rads are copper, so can be re-cored fairly easily, although obviously it's not cheap. Water pumps are almost bulletproof, with the impeller being metal, (cast iron, I think).

 

So I did a little more trouble shooting.

I grounded the temp gauge wire at the sending unit and it goes to full temp (right). I also brought an infrared thermometer home from work to double check the temp reading on the gauge.

I warmed the engine up just sitting in the driveway to check the fan clutch and it will still get up to 100 on the gauge pretty fast. The fan clutch did not appear to be working, but I am not yet convinced it is faulty because the clutch itself did not feel hot. I don't think the clutch and radiator are getting hot enough to engage the clutch and/or the aux fan.

This leads me to believe that the coolant is not circulating properly. So the clogged radiator theory is still a possibility, along with a bad water pump and blockage in the engine block.

I have not located and removed the engine block drain plug, which I definitely want to do before refilling with new coolant. The service manual does not give a location, but I remember reading a thread about it being in the lower side of the block. I will find it tomorrow and drain the block.

Am i correct in thinking that the coolant circulates from the block to the top radiator hose, then through the radiator and out to bottom hose to the water pump? If this is correct, shouldn't I be able to remove the top hose and thermostat with the rest of the system still mostly full, then run the engine to see if the water pump pushes water out? I tried this and nothing comes out.

 

there is a block draining **** on the driver's side of the engine block, behind the exhaust manifolds and engine oil dipstick tube, you turn it open and coolant drains.

looks like this:

 

Just a side note that I have an '86 and I don't have a petcock to drain coolant from the engine block. I just have a hex head plug that needs to be removed. It's in the same location that Jose described. Not sure which you might have, but I didn't want you missing it while you looked for the petcock if you don't have one either.

 

yes





Yes




Then I'd say you have a major blockage in flow to or from the pump or, as you speculated earlier, the pump itself is pumping. The latter would be a rare occurence on these engines....but "rare" isn't the same as "never" :-)

Cheers
DD

 

someone might have replaced the petcock with a hex plug, all Jaguar blocks had them since the late 1950's. My '65 S type has one too. Same part for 40 years. Very handy. contact David at Everyday XJ if you need one, he has a few.

careful when loosening the thermostat housing nuts, the studs have a tendency to break, spray rust blaster for a couple days before you try to losen the nuts.

 

"All"?

I'd advise caution with abolute remarks. Jaguar did change things from time-to-time.

My 87 Ser III did not have the drain ****. My 88 XJS did not have the drain ****. My '95 does not have a drain ****. I've worked on several of each that did not have drain *****. The Ser III parts catalog shows plugs, not drain *****. The Ser III service manual mentions block plugs, not drain *****. The XJS manual refers to drain ***** only (and quite specifically) on "pre HE" models.

OTOH, the XK120, XK140, and Ser I E-type that I take of all have drain ***** in the block.


Cheers
DD

 

no absolutes with Jaguars, it's whatever they had during assembly, but mine has had it since I bought it, and my S type also has one, both in the block AND in the radiator. (also shown in the Factory Manual and Parts Manual). I asked David Boger about these XJ draincocks and he says he has them. (assumedly removed from his parts engines).

 

These drain ***** are pretty much useless because the passage clogs up with crud, so it usually hs to come off, so you might as well have a hex plug. This rear area of the block gets very clogged up over time.

 

Can radiator clogs lead to a water pump becoming crap or the other way around?

 

I was able to get a radiator shop to acid clean, pressure and flow test my radiator for about $60. It's almost certain it and the block have a lot of garbage in it. Fwiw, my 87 also had a hex bolt in the block drain. While I had the radiator and t-stat out and with the block drain out I ran a hose through for an hour repeatedly poking a pick into the drain hole to unblock it until it ran out clear and strong. Between those things and cleaning the debris from the front end I've pretty much solved my hot running problems. It'll still top out at 103-105ish in traffic when using the AC on 90+ degree days, then the electric fan kicks on and keeps it right around 98-100. On cooler days without AC it stays pretty constantly around 90. Still a little hotter than I like on the hot days but I think the fan switch is a little sluggish (doesn't kick the fan until about 103 on the gauge) and I'm sure the rad isn't perfect given I had it cleaned instead of re-cored to save money.

Bottom line these are all old cars now and the XK engine has a well known habit for crudifying (is that a word?) the coolant passages if the coolant isn't well maintained and flushed regularly. Add to that the fact that in their infinite wisdom Jaguar told US dealers to add stop leak to the system yearly as preventive maintenance (so stupid, lol, it turns into a brick layer at the bottom of the rad over time) and it really sounds like your whole system just needs a thorough, thorough cleaning. Good luck and have fun with it....I did but then again I'm a little off.

 

I removed the hex bolt and flushed the block until clear. Then replaced the plug and filles with water for more testing. Then I rigged up a duct tape hose connection to the bottom coolant hose that runs to the water pump as a crude radiator bypass. Water is still not flowing out so it seems the water pump is bad. I will remove it and check it.

I will also remove the radiator and have it cleaned as advised. I just wanted to avoid removing the fan, etc. to get the radiator out, then reassemble and find out I had a bad water pump and have to remove it again.

Thank you all so much for your help.

 

The usual pump failures are shaft seal leaking, shaft bearing failure, impellor failure. In fact, those are the only failure modes that I can think of.

I don't think a clogged radiator would cause any of those poblems...at least not directly.

Other will chime in.

Cheers
DD