R300D - coolant gauge showing sub 70 degrees

[Boombang]

My R300D is showing a coolant reading on the gauge of just under 70 degrees.

Fan comes on and off as expected, rad and all hoses are getting hot, heater blows hot and I can't find any sort of airlock nor expect one given the system seems to be working.  Coolant at max and expansion tank is lightly pressurised when running and hot).

A side thought is a stuck (or missing) thermostat but I've not yet had time nor have sussed out enough to check that by montoring which hoses warm up.  That wouldn't explain not getting over 70 though.

Any other thoughts about a faulty sender (location in the submarine?) and/or the gauge, and is there a way to calibrate?

[Jonathan Kay]

I don't know which sensors your 7 has, and we might need to come to that.

Most temperature sensors work by varying resistance to earth. So you can do a quick test by locating the sensor that drives the gauge and connecting the signal wire directly to a good earth such as the engine block. What does the gauge do?

If you'd like a wiring diagram please send me a Private Message with your email address.

Jonathan

PS: There's a lot on Duratec cooling in the archives...

[SM25T]

Suspect the sender failing if it is the same poor quality one used on the k-series. It is the single wire one.

[Amos91]

Is this a new issue compared to normal?

The weather is definitely colder now and these cars can easily overcool due to the airflow.  Does it get up to 90-100C if you're stationary for a prolonged period of time?

[Boombang]

Thanks for that link - I'll do some checking on the other advice.

[Boombang]

The car is a recent purchase and for various reasons I have only been able to drive it a couple of times.

When stationary I believe it still sits at an indicated 70 degrees with the fan going on and off periodically - the day I picked up it was high 20s and crawling round the M25 the needle hardly moved once hot.

Yesterday I noticed the temp dropping when doing an easy 50-60mph down a lane, hence any mention of the a stuck/missing stat.  If the reading is miles out, as I suspect, it might not be overcooling that much and could simply be a low temp stat.

[Amos91]

Be best to double check the outputs with something like Easimap. On my Sigma, the fan doesn't cut in until the coolant just tips over 100°C. So it sounds a bit odd that it would be coming on at an indicted 70°C. 

It makes me wonder if the gauge is duff, as the ECU must be seeing high enough temps to turn the fan on.

[ScottR400D]

It's well known that the Duratec has at different times been supplied with different thermostats resulting in different running temperatures. 

My 2015 car has an 82c stat and typically runs there or thereabouts. Until it's thoroughly warmed up it will drop below 80 when opened up after a period of slow or steady running but once it's been running a while it's fairly steady. 

Later cars were fitted with engines with 95c stats, presumably done by Ford for emission reasons. 

As the R300D wasn't produced after 2014 or so there's a good chance that the OP's car has an 82c stat and should run at that temperature. I don't know if cars before that time were fitted with higher temperature stats, though, CC never seemed to worried about consistency. Others might know better. 

So, assuming an 82c stat the OP could well be seeing the result of a slightly sticking stat or out of whack sensor. Neither would need to be that far gone to show 70c but 70c is too low for normal running.

I doubt it would get to even 70 without a stat though so hopefully it's not been removed by the previous owner for some reason? 

A quick check would be to use a cheap pyrometer to see what readings you get under the bonnet on hoses etc. Not that accurate but if it's a 10c sensor error you'd see that. 

 

[Boombang]

Tracking my notes, following suggestions above.

Single pin sender in submarine.  Connecting the sensor wire straight to earth maxes the gauge out.  Earth on the submarine has decent continuity to battery earth.

I warmed the car up at 2k revs, reading continuity through the sensor you can see the reading changing as warms up.  As warming up I checked the sensor body using a temp probe and the gauge was reading within a couple of degrees all the way from 60-70 degrees .

When the sensor body hit about 70 on my temp probe with an indicated 70 on gauge the rad started to get hot, suggesting stat starting to open around then - obviously water inside will be hotter than body but still suggested stat is opening low if it should be 80?

Got it up to an indicated 78ish on gauge and red fan kicked in for maybe 15 seconds.  At that point it would sit a shade under 80 on gauge and sit there with fan coming on every few minutes.  At that point stat housing is ~85 on temp probe, slowly climbing to about 88 after 15 mins.

Hoses are all between 74 and 82 at the seeming equilibrium with car idling, outside it is perhaps 15 degrees today.

 

So that all suggests stat is opening early and worthy of a change. 

That said if the rad fan is coming on sub 80 will it not be on almost all the time with an 82 stat? 

What temp should the rad fan kick in and which sender does it use to trigger switching the fan on?

[Jonathan Kay]

Sounds as if the gauge and wiring are OK.

And probably the sensor too. But I've just changed one that worked fine as it warmed up but only intermittently when hot. 

Jonathan

[Boombang]

Thanks Jonathan - I posted my reply above this one in the garage then edited when sat back inside, so it has changed since you replied.  Do agree though gauge, sensor and wiring look fine.  Stat is opening early and the correct temp for rad fan coming on is TBC but suggested to be around 96 and this thread and post is useful... https://www.caterhamlotus7.club/comment/2136002#comment-2136002

Without Easimap and seeing what the ECU is showing it's hard to be certain, but everything points to the stat itself seeming to be worthy of a change.

[ScottR400D]

#9 I would agree that it sounds like the stat is opening early, unless it's a 70c stat!

My 82c stat shows clearly on the gauge when it opens at an indicated 82, as best as the gauge can be read. 

My fan comes on pretty soon after 80 but is only noticeable when you're stopped, pretty much. Possibly because you can't hear it anyway when you're on the move. It could well be on at other times. 

I'd change the stat for a new 82c and see how it goes. 

 

[Boombang]

To conclude this thread, forgot to update it and as advertising the car I'm assuming any prospective owner will be curious as to outcomes.

Coolant system was flushed 3 times with deionised water.

A new 82 degree race stat was fitted (short nose version).

New hose was fitted between the stat, T piece and header.

Refilled with fresh Comma Xtreme OAT coolant.

Temp sender terminal cleaned and wiring route moved.

System pressure tested and no leaks - all good for another 5 years.

[Jonathan Kay]

Thanks for adding that.

Jonathan