Yes it is now the same as factory but it came with no baffle in left tank, so coolant from B bank would have gone straight to the outlet at the bottom and back into the pump. I inserted a plate and had it welded up to make the coolant follow the correct path.
Kirby, the car is a late S2 XJ12 with no crossover filler etc. The expansion tank cap vents to an open hose so there can be no blockage and once it finds its own level it’s fine until/unless it reaches a significantly higher temp and a bit extra eventually pukes and a new highwater mark is set.
Dear Greg,
You can solve the heat soak problem this way by mobilising the cold(er) water in the radiator just after you stop. Solving heatsoak - a worked example
kind regards
Marek
Yes, thanks, I read that a while ago. It totally makes sense. ALL cars have a bit of heat soak, I tested my Volvos, and they went up about 10F too, from 205F to 215F. For me, it’s important what that final heat soak temperature is. I wouldn’t want to shut off my motor at 215F and let it climb to 225F, so of course I would do the heatsoak solution.
Instead I run cooler thermostats (180F) and cooler aux fan thermostat (comes on at 190F radiator temp, which seems to be about 200F coolant temp). On the majority of my drives, when I shut down the engine, it’s between 180F-195F. So my heat soak is never above 205F. That heat soak temp is harmless to me.
Only ONCE was I about to shut down at 200F. When I heard the aux fan was on, I waited about five minutes until it turned off, and THEN shut down the engine. My aux fan turns off when radiator temp is 174F (which seems to be about 187F coolant temp)
anyone ever want to test there Jag V12 cars ,just bring them to Texas in middle of August!
runem on I-10 west for 30/45 minutes at posted speeds 75/85 mph! then pull into a stop area, shuter off and wait for 10 minutes or so!!
if no boil and gurgillin , she is a cooler , NOT a boiler!
ron
excerpt from TWR racing the XJS V12 cars! i’m quite sure they know a little about these cars!! oil%20cooling%20001|476x500 .
oil cooler more important than radiator cooling!
my V12 oil is always after a 1/2 hr run around 30/40F hotter than coolant temps!
ron
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
26
It’s supposed to be. Motor oil needs to run hot enough to boil away any moisture that collects in the crankcase. If it doesn’t, the moisture degrades the oil.
Boiling isn’t required, but heat is. You still drive condensate off below 100C
Around town in slow traffic the oil is normally at or slightly below coolant temp IIRC as there’s not a huge amount of flow. At high speed the oil is hotter than the coolant.
So who’s going to be first to try 0W-20 in their car’s cooling system? No boiling over…
Back to the topic, In verifying my cooling system I have been testing sensors and thermostats. I found two temp sensors on the left side head. One is a Bosch sensor that is open at ambient temp with no response when heated to boiling. I ordered a replacement. The other is an Otter switch with a 7/8" fine thread about 4 inches rearward of the Bosch switch. It reads about 1.4 ohms ambient to boiling. I have searched wiring diagrams, manuals and archives and can find no reference to it. It has the same 2-pin connector as the well-known Otter switch in the pump intake. I suspect it was used for a US-only feature (air-pump diverter?) that is no longer on the car. I jumpered the wire connector contacts with the key on and nothing lit up or came to life. Does anyone know what this sensor does? Its two wires (Blue with Green stripe and Black) go into the same harness as the Bosch switch.
If, as I suspect, the switch isn’t needed anymore, would this be a good place (just upstream of the left thermostat) to put a thermo fan switch for the new main electric fan I plan to install? The thermostats open at 180 degrees. What temp should the new fan switch on? I’m thinking somewhere between 185 and 190? The small aux fan switches on at 190. Any thoughts appreciated!
Tony
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Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
31
No. That location senses engine temp, while what you need for operating a fan is radiator outlet temp.
On my '88 V12 (US market), the first front sensor on the left side (B bank) is the CTS for the ECU.
The second one a few inches behind that was for the charcoal canister system for the fuel tank vapor. I can’t remember exactly what it’s for, perhaps it opens a vacuum valve once engine is warm enough? I removed it and did put a new sensor for an aftermarket coolant temp gauge.
OK, that does make sense…control the fan by sensing the temperature of the output of what it is cooling. So, I will simply add a relay and have the pump inlet sensor switch it on in parallel with the aux fan relay -the red one. I have a new sensor coming, later style that’s threaded to replace the grommet-held Otter switch. Need to have the pump inlet housing machined to fit the new sensor threads -unless someone has a spare, later style, threaded sensor pump inlet kicking around. New ones are no longer available. If so, name your price!
My B bank temp gauge sender is where the vapor recovery sensor used to be (a few inches behind CTS on cooling rail)
My A bank temp gauge sender is where the air pump sensor used to be (rear part of cooling rail)
As the engine warms up, one of the banks (can’t remember which one) is a wee bit hotter (maybe 3-5 degrees diff), but once car is warmed up, they are pretty much identical.
At long idle, they both creep up to about 195F. When driving, they both go down to 180F (what my thermostats are)
I’ve flushed system, all new hoses and thermostats, but still running original pump and radiator.
Replaced yellow fan with new black fan, new fan clutch, and replaced aux fan with aftermarket.
For interests sake, I installed temp sensors in each of the thermostat outlets (upper hoses) and a dual digital gauge for readout in the cabin. (I think JamesLove has the same/similar setup?)
During warmup they both read essentially identically. But once hot, without fail, the B-bank is around 3 degrees Celsius warmer than the A-bank. I have 80deg stats installed. So during cruise they read around 80/83, and during stop and go climb to around 89/92 deg C. I have twin electric fans controlled by rad outlet temp.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
37
Keep in mind that the coolant entering both banks is exactly the same temperature (coming from the same pump) and the same pressure. There are only two ways one bank can end up a few degrees hotter than the other: 1) That bank is generating more heat than the other, or 2) The flow rate through that bank is lower. Presumably the flow restrictions are similar between banks within the engine, and the flows are together through the bottom 2/3 of the radiator and into the pump, so pretty much the only possible reason for lower flow in the B bank is the additional restriction of flowing through the upper 1/3 of the rad.
I completely agree, what I found interesting was to quantify what the temperature delta was between the two banks at the outlet. The identical temps during warm-up support the hypothesis that the cause is the additional restriction of the upper 1/3 of the radiator. As of course the entire rad is essentially bypassed during this period.
What I don’t have is any data on what the temperatures are in; 1) an OE brass rad, 2) a marginal system, and 3) what role plugging of lower rows of tubes have on temperature delta between banks.
Being only 3 degrees between banks in a clean system means that the additional complication involved in converting to a single pass system is IMHO just not worth it, provided the system is maintained!
Don’t laugh but I even considered putting an additional temp sensor in the water pump suction line (I don’t use the fan thermo switch there anymore and have it plugged) just so I could geek out and watch the whole system work!
I’m thinking it’s like back pressure in an exhaust system where a hypothetical engine has two pipes going into one muffler and one of the pipes has an small muffler before the shared muffler. That side might run hotter.
It would be interesting to construct a radiator that had the left tank baffle plate halfway down instead of a third. That would reduce the left bank restriction and present some equalizing back pressure to the right bank. If temps also equalized, that would support the flow difference theory.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
40
No, it would not. It would reduce the left bank restriction, but then it would add restriction to both banks, Both banks flow through the lower part of the radiator, remember?
This is why I added a restrictor of sorts to my RH coolant filter. I used Gano filters (obtained before I knew Tefbas existed), and screwed a 1/2" ID stainless steel flat washer to the inlet of one of them. Didn’t really notice any effects at all, but of course I didn’t have the temp sensors that pwstoneman has. Theoretically, the right bank should have gotten a hair warmer and the left bank should have gotten a hair cooler. If the restriction was exactly correct, they’d end up at the same temp. If it wasn’t restrictive enough, they’d get closer but still not equal. And of course, if a 1/2" orifice was too small, the A bank would overheat. 1/2" was clearly not too small, though. My suspicion is that it was so much too large that it scarcely made any difference at all to the temperature differentials.
