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I have an all new cooling system. New radiator, water pump, hoses, thermostats, heater valve, water rails, AAV, et cetera. The only things I left in place were the engine and the heater core. Its finally stopped raining long enough to finish it and I've been able to run the car. The car warms up and the electric fans come on, so I know I wired that correctly, but the gauge (oh the lovely reliable gauge) shows just over N, maybe a needle width above. The fans come on and off, but don't stay on long enough to drop the gauge. I don't think they're supposed to, just lower the intake coolant temperature. Here's my concern. I fitted 90C thermostats because that's what I misorded. I meant to get 88C, and I didn't think 2 degrees would make a huge difference. When I took everything apart the car had been running 75C thermostats. Under normal conditions it would be halfway between C and N, rising through N in traffic. Which is why I decided to replace everything. Using an infrared thermometer the highest reading I can get is on the cross pipe. Its holding steady at 94C.
So since the thermostats are the thing that changed, they're most likely to be the cause, as opposed to the gauge. Right? Or, did I break the temperature sender while working on the water rails? I'll probably replace it anyway, its only $10. I did replace the connector to the gauge, it was loose, and that brought the displayed temperature down about a needle width.
I have an all new cooling system. New radiator, water pump, hoses, thermostats, heater valve, water rails, AAV, et cetera. The only things I left in place were the engine and the heater core. Its finally stopped raining long enough to finish it and I've been able to run the car. The car warms up and the electric fans come on, so I know I wired that correctly, but the gauge (oh the lovely reliable gauge) shows just over N, maybe a needle width above. The fans come on and off, but don't stay on long enough to drop the gauge. I don't think they're supposed to, just lower the intake coolant temperature. Here's my concern. I fitted 90C thermostats because that's what I misorded. I meant to get 88C, and I didn't think 2 degrees would make a huge difference. When I took everything apart the car had been running 75C thermostats. Under normal conditions it would be halfway between C and N, rising through N in traffic. Which is why I decided to replace everything. Using an infrared thermometer the highest reading I can get is on the cross pipe. Its holding steady at 94C.
So since the thermostats are the thing that changed, they're most likely to be the cause, as opposed to the gauge. Right? Or, did I break the temperature sender while working on the water rails? I'll probably replace it anyway, its only $10. I did replace the connector to the gauge, it was loose, and that brought the displayed temperature down about a needle width.
90c is a tad hotter than I would use, and 75c is the old carby spec stat, oops somewhere in its past.
I run those 82c, as mentioned in the Sticky, and my "reliable" gauge sits a needles width under the N when moving. Gets to the N when the Thermo kicks in, and that lasts a few seconds, and the gauge sits around the same, and drops back as soon as I move off.
Summer, 45C, and A/C on, gauge sits at that blow N all the time, as the LH fan always runs with the A/C.
Infra Red, NAH, never had one, you can "smell" an engine running hotter than it should, of is that Old Age, whatever, it works for me.
Instrument clsuter extra earth wire would possibly make things a tad more reliable.
Temp Sender, replacement would be smart, they are Lucas, and old now.
Living and driving in summer hell...read that Phoenix AZ...for 15yrs in a 93 4.0. I wish I had a motor that ran a temp gauge on dead N in traffic! After all this time, I find "consistency" is my rule. As long as my gauge doesn't go far right in stop-and-go, I'm good. Insure the belts, coolant level, and associated parts are attended to and maintained as with any other system and just enjoy the car.
The problem could be the thermostats, but not the temp rating. Many (or most) thermostats listed as fitting the XJS are too short to fully shutoff the bypass. When I replaced my thermostats with the correct ones, it made a pretty significant difference in cooling efficiency -- from Mid N to halfway between C and N during normal driving. No other work was done at the time, so that was exclusively the difference correct stats make.
After a lot of searching for the proper spec thermostats, Gates 33188S were the easier to find and other forum members had good experience with that model. I'd recommend trying them and see if that doesn't make a difference.
I changed the temperature sender and things improved visually. Letting the car warm up idling the temperature rose steadily to the top of the N, and then the fans came on. I ran the engine for 10-12 minutes and it stayed steady. I took the car for a short drive, about three miles, and the needle was right in the middle of the N the whole time, only returning to the top when I got home. The last bit of the drive was a good sized hill. The V12 can sure pull! On parking the needle rose a little bit from the pre-drive position, but barely. I did notice a bubble of coolant coming out when I removed the sensor. It quickly stopped flowing, but I'm wondering if there was a little air bubble in there.
With the stats you have, that would be more than acceptable.
Yes, there is still air in there, normal, usually takes 4 to 5 drive cycles to "burp" it all out, and even then it will only be 98%, roughly, ""burped".
The more its driven, the less air it builds up, its just how they are.
It makes a mess but you really have to take your time and let ALL (as much as possible) of that air get pushed out... Fill it slowly just as the great GF describes...
I have a question about orientation of your thermostats... wiggle pin UP, I hope...?
Also, does you car idle at 1000? If so, idling and parked, it will get hot. Maybe bring the idle down some?
I don't know how accurate those barrel gauges are. My 91/5.3 had two Auto Meter (AM) temp gauges, one sender in each water rail. When the barrel gauge was touching the bottom of the "N" both AM gauges read about 215 F, & that's in Florida summer heat. Your barrel temp gauge needle is well above that N. That would be around 250F in my 91 . As sald, I'd check both fans, clutch & electric & that 1000 rpm
On another cooling question, does anyone use the Lutz Mods. I never see anything about them any more. I installed the Lutz 1 when I installed SS water rails. Any difference ? Don't know, but never ran hot or dropped a valve seat
The car is not at 250F! The barrel gauges are inaccurate but give repeatable readings; just get a temp gun on the tophose and find out for sure what the temps are at a a given gauge position.
I don't know how accurate those barrel gauges are. My 91/5.3 had two Auto Meter (AM) temp gauges, one sender in each water rail. When the barrel gauge was touching the bottom of the "N" both AM gauges read about 215 F, & that's in Florida summer heat. Your barrel temp gauge needle is well above that N. That would be around 250F in my 91 . As sald, I'd check both fans, clutch & electric & that 1000 rpm
On another cooling question, does anyone use the Lutz Mods. I never see anything about them any more. I installed the Lutz 1 when I installed SS water rails. Any difference ? Don't know, but never ran hot or dropped a valve seat
Many moons ago, 15-18 years maybe, some of us took IFR readings and barrel gauge readings and compared notes.
On my XJS the bottom, middle, and top of the N was [something like] 180F, 190F, and 200F respectively....which seems normal/sensible/expected. Others had results varying as much 10º-20º from mine!
Garett reports that the highest reading he has seen on his IFR is 94ºC and it holds steady at that temp. I maintain that, if that's as hot as it gets, there's nothing to worry about...especially since it isn't climbing up-up-up with no end in sight.
A few things that I'm finding concerning. I lowered the idle speed to about 800 and the engine became a little lumpy, maybe 11 cylinders lumpy. The lower idle speed has shown up a problem with my alternator change, it discharges bellow 1000 rpm. Part of that is definitely the battery terminals. They need to be replaced as I can't get them tight on the posts. I bought replacements, I just haven't installed them. I think that project is moving up the to-do list. The hottest reading I can get in still about 94C, but its in the coolant crossover pipe. Maybe its hotter because its steel, as opposed to aluminum or rubber, but maybe its still got hot coolant going through it even when it should be closed off. I did order new thermostats, just to have on hand if I gave up on the current ones, they'll be here tomorrow and that may become my weekend project.
On the lumpy idle, the injectors were cleaned professionally 18 months ago when I bought the car, and new plugs, wires, distributor cap, and rotor were installed then too. The EFI harness looks to be original. Someone pulled it up out of the V at one point, but its got some patches to the insulation and is probably well beyond its best by date. So there's something else to test/replace. The exhaust has smelled a bit like unburnt fuel, but I thought that might be something like the timing being off a bit. Oh, I'm sure it is off too.
A few things that I'm finding concerning. I lowered the idle speed to about 800 and the engine became a little lumpy, maybe 11 cylinders lumpy. The lower idle speed has shown up a problem with my alternator change, it discharges bellow 1000 rpm. Part of that is definitely the battery terminals. They need to be replaced as I can't get them tight on the posts. I bought replacements, I just haven't installed them. I think that project is moving up the to-do list. The hottest reading I can get in still about 94C, but its in the coolant crossover pipe. Maybe its hotter because its steel, as opposed to aluminum or rubber, but maybe its still got hot coolant going through it even when it should be closed off. I did order new thermostats, just to have on hand if I gave up on the current ones, they'll be here tomorrow and that may become my weekend project.
On the lumpy idle, the injectors were cleaned professionally 18 months ago when I bought the car, and new plugs, wires, distributor cap, and rotor were installed then too. The EFI harness looks to be original. Someone pulled it up out of the V at one point, but its got some patches to the insulation and is probably well beyond its best by date. So there's something else to test/replace. The exhaust has smelled a bit like unburnt fuel, but I thought that might be something like the timing being off a bit. Oh, I'm sure it is off too.
As far as I remember my xjs will not run with the battery terminals disconnected... from what I (the great me) remembers (and that ain't much)...
What I have done in the past when new terminal wires are on the list and the ones i had wouldn't clamp down properly on the posts is take a small screw (big enough) and run it down between the clamp and the post. It'll make good contact on the screw side and draw the other side tight as well. That's IF they are not tooooo loose and completely shot. Not a permanent fix but was usually enough to get me by.... maybe it'll smooth things out...? Before doing this wait to see if someone can correct my thinking on this...
I'm sorry my idle suggestion revealed more head scratching. I am, and can relate... you'll get it and get there! No doubt.
I knew the idle was high, and I wasn't sure it was as smooth as a V12 should be. The idle speed was masking the issue, but I'm not surprised this issue popped up.
That crosspipe will have some flow, not much, as the stats do close the By-pass ports, that lead to that pipe, when operating temp is reached, IF the stats you have installed are "long enough". That is in the stickie at the top I believe. The flow in that pipe is at its Max when Cold, and decreases as the stats close off that port in each rail.
Roughish idle. That list is long with an unknown car, and yours being Lucas is soooo simple to sort.
It runs, so the timing is close. Read the attachment, that is teh ONLY way to time one these days.
Alternator dropping off below 1000rpm, its Lucas, and OLD and simply tired. Time for an upgrade to 110Amp. The Lucas is possibly? 75amp, and the exciter circuit is out of date. Many threads on here related to your market regarding which to use etc etc. Down here Bosch from XJ40 was the go way back when.
If its 100% got a misfire, and the list you have is factual, then the EFI loom is highly suspect.
While you have nothing to o, take a REAL GOOD look at the engine EARTH straps, at the LH engine mount bracket area, make 200% they are intact and CLEAN, and TIGHT. Run a dedicated earth strap, engine to chassis, sleep peacefully.
Great call on the ground strap Grant! I’m not sure how tight it is, but it’s not clean. As part of the cooling system refurbishment I replaced the alternator with a GM CS130. I put it where the air pump was, sharing a belt with the ac. It turns a little too slow to charge well at idle, which I was aware of going in, but the battery terminal looseness is exacerbating the problem.
So I removed the bolt from the battery cable terminal, pried it apart with a screw driver, and polished the inside with a brush on my Dremel tool. I was then able to get the terminal to hold the post properly. I can no longer remove it with just one hand. Then I tightened the alternator belt, it had stretched a bit since installation. With a cold engine idling at 900 rpm, its a little over 13V and charging. It was down at the red yesterday, so hopefully I'll be able to lower the idle speed without loosing too much charging ability. When I installed the alternator I did install a dedicated ground for it, so that it wouldn't have to ground through the mounting bolts and engine. Now I'm off to buy a new ground strap for the engine.
The bad news is that my new thermostats showed up and... they're exactly the same as the ones in the car. I ordered the wrong ones twice.
When you get home and consumed alcohol to address the thermostat fiasco:
Look at the Earth connectors alongside the battery, they are usually forgotten, and so sad. White "growth" is common.
Then, up the front, clean the many that are associated with thw bolts of the radiator top support panel, usually sad also.
Last edited by Grant Francis; 09-04-2021 at 06:37 AM.
When you get home and consumed alcohol to address the thermostat fiasco:
Look at the Earth connectors alongside the battery, they are usually forgotten, and so sad. White "growth" is common.
Then, up the front, clean the many taht are associated with teh bolts of the radiator top support panel, usually sad also.
08-29-2021 | 12:12 PM
Running "Hot"
