"New Style" Temperature Sender - Anyone swapped, reading differently?

[revilla]

Has any body swapped their "old style" temperature sender for the "new style" one as shown here, and if so have you noticed any difference in the temperature readings on the gauge?

Having been suffering from a bit of what I thought to be hydraulic lifter noise, I've tried changing over to a 10W40 DIESEL engine oil for a short time to see if the higher detergent levels would clean the lifters out without me having to strip the head. It appears to be working, the lifters seem to settle a lot quicker on startup and the valve gear sounds smoother every time I drive it. Only done about 200 miles on it so far, will leave it in for a while to do its job.

Whilst I had the oil drained, I changed the temperature sender (I have an extra "water" temperature sender in the oil filter housing and a switch to toggle the gauge between water and oil readings) as the old one had gone on the blink. The latest sender is a different design with a nail-head connector in place of the old spade.

Since swapping over, the oil temperature has been reading noticeably higher. Since I have changed two things at the same time, I don't know whether this is because it is actually hotter or just because of a difference in calibration (or both). I suspect a bit of both to be honest, the oil pressure is a bit lower on the same grade of oil so I think it is running a bit hotter.

I was just wondering if anyone could confirm whether they had experienced any change of reading when switching senders?

Oil is not over-filled so no reason to believe it's crank thrashing. Oil is same grade as that I normally use, i.e. 10W40 semi synthetic. The thing which leads me to wonder about the sender is that the oil temperature reading only varies a little depending on driving style, just as before, but it now sits steady at about 10 degrees hotter than the water reading (which is still using the "old style" sender) where it used to sit at almost exactly the same reading.

So long as it doesn't start getting stupidly hot I think I will stick with this oil until there is no further change, then go back to my good old Magnatec.

[Jonathan Kay]

Back to basics: how about testing both senders in a rig with a thermometer? Kitchen, oven and cooking oil?

Jonathan

[revilla]

Yes, I could, but to be honest I don't want to have to drain the oil and (some of the) coolant yet again to test them. I've only just got the car back together after a major rebuild / rebush of the rear suspension and I just want to enjoy driving it a bit!

I could test them when I drain the oil to switch back to Magnatec later on - but I guess I would get my answer at that point anyway.

Was just wondering in the meantime if anyone else had noticed anything that might add up to a pattern?

[makingff]

Hi Revilla

As part of my attempts to resolve my water temperature gauge issue (see other thread), I've used every pretty much every type of sender that is compatible with the gauges.

The 'old' style ones are pretty pants and seem to fail regularly. The 'new' style supplied is much more robust and the one Caterham supply is listed as 150 degrees (which I had assumed would lead to an incorrect reading). Therefore, I also bought this which is listed as 120 degrees.

Each seemed to show the same reading and I'm now running the 'new' style Caterham one and have ditched the last of the 'old' style ones as the core was loose. I have 2 of the 120 degree ones in my box of spares.

Hope this helps.

Simon

[revilla]

@makingff - Thanks for that. So there's no significant difference in calibration between the units you tried, including the "old style" and "new style" Caterham senders. In which case it confirms that my "cleaning oil" is running quite a bit hotter than Magnatec for some reason and I need to be careful. Thanks.

The associated reduction in oil pressure when hot also seems to suggest that it is getting hotter but I wasn't 100% sure that the viscosity gradings used for engine oils for diesels and petrols were exactly the same.

Will take things gently until the valvetrain noise has settled completely then go back to Magnatec I think. The engine seemed to be pretty happy on that.

PS: I can't find any explanation as to why it would run hotter on a diesel engine oil of the same grade.

[makingff]

Hi Revilla

A quick scout around the web leads me to believe that petrol engines run at a higher temperature than diesel engines. Therefore, my assumption would be that diesel engine oil is not designed to cope with the heat generated by a high reving petrol engine and would create higher oil temperatures (which is what you are seeing). I have to add that I can, in no way, be considered an expert - it just seems logical to me.

I always use the Comma Motorsport 5W50 oil.

Simon

[revilla]

Yes I guess diesels don't rev to the same levels as a K Series either, so operating conditions will be generally quite different. I read about the trick of using a diesel oil on several MG & Rover forums, the idea being that diesels generate a lot more soot which through blow-by gets into the oil, so oils intended for diesels contain high levels of dispersants and detergents to keep these in suspension and prevent them from clogging oilways, lifters etc. I was suffering from what I thought was a weak hydraulic lifter and people seemd to swear by this trick to clean them without having to strip the head down and so it seemed worth a go.

I generally use Castrol Magnatec 10W40 Semi Synthetic; reading through many many posts on the same forums as above there were many anecdotal stories of premature failures of the VVC drive mechanisms on fully synthetic oil (although no technical explanations offered). These are highly stressed and fairly complex little mechanisms and the consensus seemed to be that although the bottom end, being like any other K Series, was happy on 5W50 synthetic motorsport oil, the VVCs specifically preferred 10W40 semi synthetic. This may of course have been just correlation rather than causation; it may be that the people who tended to put motorsport oils in their engines then tended to take them out for a good thrashing! Before reading any of this I did however once do an oil change onto the Comma 5W50 and the VVC drives were noticeably more chattery - which is what lead to me to research this and switch to Magnatec semi synthetic 10W40 at which point they quietened down again, so there may be something in it.

Initially I had a really rotten valvetrain rattle on startup which got better but didn't disappear as the engine warmed up. If you revved then engine for a bit when warm it would go away but then slowly return if left at idle, so I was guessing the increased oil pressure was improving the feed to the lifters but they were still bleeding down very slowly at idle.

After about 200 miles on the diesel oil, the rattle is sgnificantly better on cold startup and fades away on its own after a 30 seconds or so to a minute of idling. When hot the engine sounds much less "tappety" and generally smoother and the rattle doesn't return like it used to. Consensus seemed to be that it would take a good 2000 miles to do its job properly, so such a noticeable improvement after only 10% of that is encouraging, although knowing the sensitivity of the K Series alloys to overheating the higher temperatures do concern me a bit; however if it really is giving the engine a good clean out then I'll live with having to drive it a bit more gently for a while. Later in the summer I will definitely switch back to Magnatec.

On Magnatec the water would generally run at an indicated 85C and the oil at the same when driven gently, slightly higher at maybe 90C after a long run on a dual carriageway. On this oil the water runs at 85C and the oil at about 90C when driving gently, rising to nearer 90C water and around 100-105C oil after a long fast drive.

I'll see how it goes. What's the worst that can happen? ... Err, on second thoughts, don't answer that!

[Jonathan Kay]

Very interesting... but how much oil or water do you have to lose when swapping a sender? (Videos welcome!)

Jonathan

[revilla]

OK ... not much ... I'm being lazy!