Running temperature

[cliffordl]

Having got CF25 up and running my thoughts now turn to how well it runs.
   What are acceptable temperatures for the oil and water guages to read after a reasonable distance?
   
   Also my diff is on the way out. I've obtained a 3.07 IRS diff, is this a suitable replacement?
   
   Best
   
   Clifford.

[Emmanueld]

Hi Clifford,
   
   Water temperature should be right below 90c and oil as well. My friend Jeffrey's oil temp runs well above that and I think it's too high.
   As far as the diff, I dont understand what you mean? You want to replave the whole unit or just the gears? The automatic Frua uses a 2.88 gear set and a limited slip differential. The housing is Salisbury, similar to a Jaguar E-type but not exactly the same. (Different mounting holes) It is the same as the Cobra and MKIV units. Check your half shafts and wheel bearings they have a tendency to go bad when the car sits too much. The diff is bullet proof!
   
   Emmanuel

[cliffordl]

Now I,m confused, my mechanic noted the car "jumping across the road" when driven at reasonable reversing speed and blamed the diff. He suggested that it is the same as the jaguar V12 IRS diff. I located a 3.07 IRS diff that I was told is popular with Cobra builders.
   Is this not the case?

[Emmanueld]

Hi Clifford,
   
   No the diff is not the same with the E-type, it is similar, the mounting holes are different. Internally, they are probably the same (With the exception of the ring gear of course). The rest of the suspension is completely different though. The only similarity is that it is independent and the Cobra set up is far superior to the Jaguar system because the axle is supported by both an upper and a lower control arm. If there is a problem with the differential, have it rebuilt. The kit car people use a Jaguar rear end because it is the only affordable self contained independent suspension available; otherwise they have to use a solid axle. If there is something wrong with your differential, any good shop can open it and fix it. You could even install a Quaife limited slip which is the best available for your car (about $1500) or a Detroit locker available new here for about $500. Kirkham Motorsports carries all these parts. Stay with the original differential casing, you will be happier in the long run and it will keep the car original for value sake.
   
   Make sure there is no play in the wheel bearings and the bushings holding the rear upper and lower control arms are tight, if a wheel is allowed to move forward and backward when you accelerate, you will get the same feeling. []
   
   Emmanuel

[cliffordl]

Thanks Emmanuel will do.

[freddie]

Clifford
   I saw your car at Bonhams. Both rear wheels were a way out of line. One was toe-out so much it looked like an old BMW 3 series (that was the N/S i think). On the otherside the wheel was not pointing in anything like a straight-ahead position, it was sticking out towards the front. The diffs on these can be really bad news if they're not in properly, may i suggest you talk to/take it to Thunder road before getting further involved....
   Good luck

[cliffordl]

Thanks for all input so far.
   
   I have ordered a replacement aluminium radiator and am fitting two kenlows in front to push air through the rad so hope to solve the cooling issue.
   Diff is being re-built and am trying to track down new bushes for the tie arms. Any suggestions?
   Meanwhile the water temp. sender is rather bizarrly located in the expansion tank giving an under-reading. Was this standard and is there somewhere else to locate it?
   
   Cliff.

[Mark IV]

Temp sender should be in the front top of the intake manifold, there is a threaded boss located there for it. If the temp guage is mechanical (as I recall from the AC 428 I had, it was) you may need an adaptor to go from the pipe thread of the intake to the straight pitch of the sender bulb retainer, any good ironmonger should have the stuff you need.
   
   Also do not fall into the error of not running a thermostat, you will have LESS cooling without one as the coolant circulates to fast to properly effect the heat exchange required.
   Rick

[Rheinubung]

Hello Clifford:
   
   What is your source for the aluminum radiator replacement?
   
   Regards,
   Rheinubung

[cliffordl]

My local specialist outsourced it to Guildford Radiators (who make for Lotus racing) here in the UK.
   
   The existing rad has, 4 row, 13.5 mil tube centres with 8 fins per sq. inch and no louvres (I am told). The new ally rad will be 2 row, 9 miltube centres with 16 fins p.s.i and is louvred. Should be at Least 15-20% more efficient. Ten day turn around time. The downside being the £550 price tag. Once installed I just need to work on getting the heat out of the engine bay.
   
   Let me know if you need contact details and I'll put them up on the forum.

[Emmanueld]

The sender is located on the header tank, The stock radiator is fine providing it is free of scale inside. Make sure you use a 160, 165F thermostat.
   
   Emmanuel