I'm a new member although I have viewed the site a few times and I'm impressed with the exchange of info. I'm having a love/hate relationship with my 1975 series II XJ6 4.2 L (European spec). The past three years have seen a complete body strip-down and respray, new suspension, overhauled steering and braking. Most recently the head has been redone and timing set. All pipes and hoses are clear, the water pump, although slightly pitted, is moving freely, radiator is serviced, the thermostat is removed and the system has been flushed 3 times. After 15 minutes idling or approx. 5 miles driving the engine is overheating (climbing above Normal). Additionally, the heating is ineffective. The problem coincides with the removal of the fan about six months ago so I'm leaning towards a problem with the fan fluid coupling. However, my understanding is that the fluid coupling kicks in at low revs rather than at high temperature, which does not account for overheating on the open road. Should I noticeably hear the fluid coupling kick in/ kick out? (I've stood over the engine and the fan speed seems to remain constant). I should mention that my daughter's request for transport at her impending wedding is not exactly lowering the temperature. I would greatly appreciate any suggestions/advice.
Brendan

 

When you say you removed the thermostat, did you remove it and replace it or are you running the car without one?

 

Brendan,

Welcome to our world.

As Mikey said, there MUST be a thermostat, of the correct length (and Jag it very wrong a few years ago) or the thing will NEVER run cool. No thermostat, or the wrong length stat, will see 30%+ coolant never go via the radiator, and engine temp will simply continue to rise, as there is NO control from said thermostat.

I dont see where the radiator has been removed and dissmantled and professionally rodded and cleaned, this is a MUST on these cross flow radiators.

The fan hub thingy is an iffy item at best. The simple test is to have the car hot, shut it down, manually give the fan a flick, it should have resistance and rotate about 1 turn.

The steel fan on the S2 was marginal at best, hence the plastic fan on the S3.

The pressure cap integrity is obviously a very important item, and will cause overheating if incorrect. I doubt that is the case here, just saying. The filler blank cap on the S2 was/is a PAIN, and there are many alternatives available, mainly in the UK.

Air in the system may be an issue, but the S2 6cyl did not suffer from bleeding issues in all mine that I once owned.

Radiator clogged internally, as I said, is the #1 issue with them.

 

Forgot, I do that.

You mention that you noticed NO difference in the fan speed whilst watching it, which kind of screams fan clutch to me. Also the fan clutch does increase resistance based on the hot air coming via the radiator. It never locks up completely, but does "stiffen up" significantly.

Feel the bottom hose, once the engine is hot enough, is it hot to the touch, or coldish?. It should be cooler than the top hose, coz the radiator has "cooled" the fluid.

 

Since you mentioned that the heater is not working, I am thinking that the system is airlocked or the water pump is not circulating coolant properly.

 

A bit of clarification on fan clutches....

A Ser II (or early Ser III) should have "non-thermal" fan clutch.....identified by the single bolt thru the enter. This type is not temp sensitive. It is designed to be and stay engaged until a certain RPM (2500? Guessing) is reached. At that point it beings to slip.

The "thermal" type has four mounting bolts and the little heat sensitive coil spring thingy at the center, facing towards the radiator. This is type that slips until "xxx" temp is reached...at which point it engages firmly to pull more air.

However, neither type should free-wheel. The hand spin test is good but with the thermal type you have to check it hot, as mentioned.

It's a rare day that I can add anything once Grant has already chimed in. I'll admit it....I'm chuffed

Cheers
DD

 

Thanks Doug,

It is all memory now, those were the days.

ALL my Jags ran thermo fans from basically day 1 of ownership. I hate engine driven fans with a passion. the hardest to adapt was the '64 S Type, there is simply NO room in there for anything, and then I air cond the thing, must have a drinking problem that day, what a nightmare.

 

I hate to be repetitive, but he has stated that the heater is ineffective. Coolant is not circulating!!!!

 

Yes, and NO stat will do that, as well as a stat that is too short and not closing the by-pass port.

Since he is in Ireland, they are still asleep, give him a few hours, maybe more.

 

Many thanks for the suggestions. The radiator has been professionally stripped and the fluid coupling is centre bolted with no coil spring. The thermostat is completely removed - I assumed this would allow free flow throughout the system. If air lock is a problem, how do I go about bleeding? Also, if the heater matrix is clogged wouldn't the coolant still circulate around the block? (I'm toying with by-passing the heater but I dread the thoughts of tackling the matrix itself). Just a thought, is there any way I can check the circulation via some kind of flow meter? I'm out of action today but tomorrow I'll run some tests (refit the thermostat, check the bottom pipe, pray).
Brendan

 

OK, no stat is no good, the coolant travels the system too fast to be cooled. The stat is a flow restricter as well as a temp controller. The S2 onward, has a by-pass port up inside the base that the stat sits in. My memory is that the distance from the mounting flange TO that port is 41mm. Most Jag stats some time ago were only 39mm when fully open, NO good. I use a Ford stat that is 34mm when closed, and 43mm when fully open, and thus closes that port 100% as it opens, which is critical for proper cooling system operation. The Dayco # is DT18A.

The heater core is simply flushed, by using the garden hose, and reverse flowing it a few times, with the firewall hoses removed so the mud goes on the ground, not back in system.. Usually heaps of mud comes out of them. Blanking the heater is not a good idea, as the heater does aid the system in cooling that engine. More relevant in the V12 versions, but still needed in the 6 in my opinion.

I think the fact the radiator has been addressed is a very good sign.

The 6 is not usually a pain to bleed, as it does so as you fill it. One of mine had issues with "burping" the air, and filling it SLOWLY via the centre cap was the only safe way. Sometimes I simply undid the drain plug in the heat exchanger under the radiator, drained the system, and started again, REAL SLOWLY. Take the small vac hose OFF the heater tap, that "should" default it to open, unless it is jammed, which is common. That tap must work to get the cooling system operating properly.

MY opinion on this one. Drill a 1/8" hole in the outer disc of the new stat, and fit the stat with that hole at 12 o'clock. That aids air bleeding significantly.

 

Tomorrow, wife permitting, I'll flush the heater and replace the thermostat (drilled hole at 12 o'clock facing windscreen?). Failing that, I think, since the radiator has to be removed, I'll replace the fluid coupling and the water pump (impeller repair kit). This may take some time since the parts need to be ordered. What else remains? I love this beast but.........

 

Ignore my query re stat at 12 o'clock. I was thinking of some other car (probably an old Beetle)

 

HA, I did that and poured another JD.

See ya.

 

Latest update - not very good. I've replaced the fan fluid coupling (certainly a noticeable difference in fan speed), flushed the heater matrix (no sludge) and tried the engine with and without a new thermostat (sorry Grant, I couldn't locate a Dayco DT18A so I reverted to a standard Jag stat, 32 mm with a hole drilled). Still badly overheating, the bottom radiator pipe is very hot and there is and no internal heater even though I by-passed the heater vacuum switch. I'm not really concerned about the heater unless it affects the water flow. I've had my trusty mechanic with me today for 2 hours and he left scratching his head. He reckons the existing water pump is ok and certainly, with the header tank cap removed, I could see a constant spray from the hole in the thermostat. At this stage I'm down to 2 options - a faulty thermo gauge / sender or the heater vacuum.

 

What do you mean by "radiator is serviced" ?

 

The radiator was professionally stripped and cleaned.

 

"Stripped" as in flushed with a chemical product, or new radiator core ?

Only other thing I can think of is lack of thermostat allows water to pass down the radiator bypass passage, and hence avoid the radiator. The thermostat for these cars is constructed to that it shuts the bypass when it opens, thus forcing all coolant through the radiator.

Did you check the block for cracking between the bores when you had the cylinder head off ? If you have cracks between any, (or all) of 1-2, 2-3, and 4-5, 5-6, then it is possible for cylinder gases to force their way into the coolant jacket and force the coolant out via the overflow tank and pressure cap.

 

Mmmmm.

I am reading all this for a 3rd time, and taking it all in.

You are questioning the temp sender, which is good. This means that the temp gauge on the dash is saying the engine is HOT, but is it really that hot??. A new temp sender is only a few $ and well worth the elimination. Of course an infra red hand held temp gauge will give temp readings that are quite accurate.

The lower radiator hose will be quite hot to the touch after running for a short time, so really means little at the moment.



This is the thermostat style you need for this engine. Note the length. Most stats open approx 9mm, so 34 + 9 = 43, which is more than sufficient to close that by-pass port. A 32mm stat will barely close it, so that is NO good. Any spare parts operation should be able to convert that number to whatever it is they sell. Any 54mm stat, that is 34mm or 35mm long with a by-pass disc will suffice here.

The heater tap opening is important in bleeding this system. If you wish to by-pass the heater, DO NOT simply join the hoses behind the engine. That will have HOT coolant from the inlet manifold travelling DIRECT to the lower hose (the cooled coolant hose), and will "pre-heat" the cooled coolant travelling back to the engine. the engine temp will continually rise, sort of a Domino effect.

I had this once with a V12, and when I noted "his" by-pass, I simply plugged the heater hose outlet at the cylinder head, and the heater end. Thus stopping flow thru any heater hoses 100%. The cooling system responded instantly, and behaved perfectly.

 

I'm not sure of the cleaning process but the radiator was taken apart and cleaned. A new core was not fitted. I didn't redo the head gasket myself but I assume the garage would have checked (vintage specialist). My mechanic is arranging a test for leaking gas although there is no sign of the coolant through the overflow or pressure cap. Can cracks be repaired without stripping the engine?

Brendan