3.8 Cooling again!

[andrewh]

hi Chaps, just taken the 3.8 for a little run and had the usual slight over heating. I noticed that the fan motor kicks in at about 90 degrees on the dial but when the car gets that warm it really doesn't run as well. Quite tricky to keep it idling and misses on pick up in traffic jams due to vaporisation I imagine. So my question is, what temp do we think the fan should kick in and do others find the same issues with vaporisation at this 90 degree area? I have the modern otter switch fitted. Also, with the original fan blade and a new correct Fosseway Alloy Radiator what do we think the temperature should come down to with the fan running? My problem was not helped by the fact that the newly restored fan motor was sticking and required me to flick the blades for it to run. Need to look at that.

[cactusman]

90 sounds a bit too hot. My car sits at just a bit past 70 deg.

I replaced my otter switch a while back as it no longer worked. The new one was useless as the car needed to get too hot to cut in and then cooler than was possible to cut out. I opened mine up to find a modern (cheap) bimetallic strip thermal cut out inside....you can buy them for a fiver from radios spares. To cut a long story short I replaced the thing with an electronic sensor that has an adjustable trip temp but a narrow difference between on and off. It cuts in at about 80 deg c And cuts out at about 72.

Touch wood mine behaves well with no vaporization issues....I use super ul as it has no ethanol in it. I would also check your thermostat and give it a good flush through too just in case there is sediment impairing circulation.

[mgcjag]

Similar being dis ussed in another post http://www.myetype.co.uk/forum/viewtopic.php?f=3&t=9508

[andrewh]

thank you chaps. I have just checked the operating temperature on the Coolcat website for my "new" otter switch and see that its at 185F which is 85C. I reckon that to be too hot for a 3.8 and by the time the car is at that temperature the fan would take a lot to cool it down to 72C which is where it runs nicely. Ummh, not sure what to do about this other than to fit a manual switch which I really don't want to do. Because my fan was sticking I really need to try it and see how quickly and how far it will bring the temp down again if it does get to 85F before kicking in. I wonder why Coolcat went for 85C as the trigger temp?

[mgcjag]

Are you just relying on the gauge to meesure the temperature.....you could really do with a digital infared themometer to measure acurate

[andrewh]

thanks Steve, I have an infrared thermometer but at this stage am relying on the gauge. I will double check with the IR in due course. I am just trying to work out why my fan motor is sticking. Dirty brushes perhaps but need to get that working perfectly first then I can carry on the analysis. Would like it it come on a bit lower temp really.

[Barry]

First off, the car gauge is very inaccurate, so never rely on that. I have a sensor stuck on to both the header tank, and top of the rad. The header tank has never gone over 88, and the rad 82. This has given me piece of mind when the gauge was about 95. I have a new Fosseway ally rad and fan.

[andrewh]

thanks, I will bear that in mind.

[JagWaugh]

Andrew,

If the coolcat unit you have is like mine it takes a standard threaded thermoswitch, 16mm according to Mike's website. You can get an 82 degree "On" switch at a local motorfactor or racing shop if you want the fan to come on earlier. 72 Deg would be too cool in my opinion. The Tstat opens at 72, ie that is the lowest temp at which coolant is circulated through the whole system. Mike may have chosen 85 because he was selling them matched to his fans, which move a lot more air than the original.

Andrew

[cactusman]

Both the temperature and oil pressure gauges are notoriously inaccurate if you are after an absolute reading. However they should produce a consistent, if inaccurate, reading from day to day so one needs to know what is "normal" for one's own car and react if either starts to read abnormally in comparison to normality.

[mark10337]

It sounds like the thermostat is the issue and not the otter switch.

The thermostat would control what temperature coolant is around the jacket, the otter controls the temperature of the coolant in the rad and thus coming in to cool the engine once the thermostat opens. The thermostat would close again and continually oscillate allowing addition of cooler coolant from the rad as the hot coolant exits it - and thus keeps the engine cooling jacket at a fairly constant temperature.

On the Series 2 the 74°C thermostat is recommended by Jaguar as standard and 82°C for colder climates.

If your rad cooling is only kicking in at 90°C that seems a little high, as the water entering for cooling is potentially hotter than that in exiting the engine. To my mind, the temperature of the water to replace the hot coolant in the engine jacket needs to be at least a little cooler than the coolant exiting. It doesn't want to be ice cold as that would run the risk of cracking the engine block (remember an overheated engine shouldn't have cold water added to the rad).

I am going to swap my otter tonight for a 74°C with my 82°C thermostat and see how that performs. That should keep the coolant temperature down ready to absorb more engine heat when it enters. Having the thermostat matched with the otter both rated at 82°C kept an absolutely steady temperature needle.

[andrewh]

All seems good again. The problem was not the temperature that the fan kicked in but that it wasn't kicking in at all! Sent it back to the chap who rebuilt the fan blade motor for me, and as good as gold sent me a replacement. All good. Seems to be kicking in at about 85 degrees and soon comes back into cooler zone. Thats for the inputs chaps.