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K Series coolant level


Jamesh

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I appreciate that this has been covered, probably numerous times in the past, but as a new member, I wanted to contribute and also hopefully learn from the wealth of experience that is clearly out there.

I recently had a problem with my 1800 K series where the radiator fan wouldn't cut in and hence the coolant temperature worryingly increased significantly at almost every junction or set of traffic lights.

The coolant in the reservoir was right between min and max lines on level ground, so I naturally assumed that this was either a problem with the fan, or something simple like a fuse. After some checking, I had proved that all the electrics, including the fan thermostatic switch at the top of the radiator were working as expected, but the fan just wasn't cutting in when needed.

I even installed a new override switch on the dashboard for piece of mind which at least meant that the car was, to some extent, drive able even if I had to manually control the cooling fan and just hope for green traffic lights.

Eventually, I worked out that it was (as usual) something simple. In my car, if the coolant is between the min and max in the reservoir, on level ground the radiator just isn't full. This in turn means that a) there is air in the system and b) the coolant switch face isn't covered by coolant and hence, rarely, if ever switches on.

I removed the small (overflow?) hose from the top of the radiator and added coolant to the reservoir tank until I saw it escaping from the radiator. Interestingly this took about half a litre but once completed, there was still a reasonable air-gap at the top of the bottle for expansion. I replaced the hose and added a drop more to ensure that the top hose was completely full.

Since then everything has been fine, fan cutting in as expected and the coolant temperature sitting at about 76deg. Ironically I have not needed to use the override switch since.

I am comfortable that everything is ok now, however I have effectively reduced the air expansion within the reservoir, which will, assuming it is not now too small to accommodate the resulting expansion, increase the pressure within the system; hopefully this is not a major concern?

Just wondering if anyone else has tackled this issue, or am i just overthinking it?

James.

 

 

 

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Hi James,

You will find lots of threads on Blatchat on the K series cooling issues.  It sounds from your post that you have probably learnt that they are prone to air locks, and your process with topping up via small hose has fixed it.   Many owners purchase and install a bleed valve (from sites on eBay) that is installed in the heater line (highest point).  My R300 1800 K Series water temp is fine during normal driving but immediately creeps up when in traffic or town conditions to activate the fan.  The fan will then bring the temp down to "normal" and switch off.   As long as the fan can bring down the water temp to the point when it switches off when the car is static (I do this test on my driveway, not stuck on the M5!) then all is OK.

Happy driving!

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Another thing to be aware of ... depending upon the year of the car, the sender for the temperature gauge is most commonly fitted in the coolant rail just above no.4 exhaust primary. When stopped in traffic there's little air flowing through the engine bay so the coolant rail and sender get some serious localised heating from the exhaust primaries leading to a false reading on the gauge, you think it's overheating but it's not!

Stu.

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Hi Brian, Steve,

Thanks to you both for your replies. I will investigate the bleed valve, I had read about this solution, but not yet had a chance to get hold of one. The sender is indeed mounted in the rail near the exhaust primary; I I hadn't considered that this could cause localised heating and false readings, but that sounds absolutely feasible.

As much as anything, I think I probably need to start to trust a bit more in the vehicle and not panic every time I see something reading slightly high or low!

Thanks again.

James.

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Totally agree with you John and a good analogy "worry gauges" especially like you say the electrical oil pressure gauge -

I've long since given up getting too excited on the actual reading per se, kerbing my interest to the movement being recorded between tick over and blipping the throttle - as long as that still showing a 2 - 2.5 bar differential I'm generally happy - as for the reading on tick over that can range between 1/2 a bar and 2 bar depending if its sulking or not.

I know I really should replace it with a mechanical gauge sometime - perhaps I should also get the dual sort of gauge which show oil temp as well to give me something else to worry about

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'Worry gauge" priceless! When I bought my car it neccesitated a 6/7 hour trip and the oil pressure was hopeless - entire trip I was "OMG this old girl needs a new engine" first job replace sender and gauge with VDO and it has brilliant oil pressure. Incidentally the VDO dude had come across this fault many times with the Caterham style as it has a spring mechanism inside that is prone to failure...Either that or he was  a really good salesperson...

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Check the small hose on the inlet valve it has a small check valve inside and this often gets clogged. Also I would change to a mechanical oil pressure gauge, the electric senders are unreliable. I used to have issues with my car getting very hot in traffic.  

I tried everything and ended up fitting a remote thermostat with an 82 deg stat. If the air bleed hose from the inlet is blocked air can become trapped in the radiator and normally the fan switch is in the top of the rad and now no longer have coolant present.

Some radiators have a bleed hose from the top to the header tank mine didn't and it was trapping air in the top of the rad causing it to overheat in traffic. The air bleed hose in the inlet manifold was blocked forcing the air into the top of the radiator.

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This all sounds very familiar. I think that this was effectively the same situation that I encountered - air getting trapped at the very top of the radiator and hence the fan temp sensor face was not being covered by hot coolant and hence not triggering the fan to switch on.

I had considered replacing the fan temperature sensor with an inline version such as this: https://www.demon-tweeks.com/lma-fan-controller-thermostat-632341 and installing line with the top hose. Presumably that is what you have done with your remote stat - or am i misinterpreting?

James.

 

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James, you should be able to fill the radiator completely and still have the level in the expansion tank below the max, and not have overheating or unstable temperature issues. Fundamentally the standard setup and level works as long as you don't have air in the system - easily achieved by having a small (3mm) hole drilled in the thermostat and filling the system via a bleed T fitted in the heater or bypass hose (if no heater fitted).

Historically there was a small pipe available from Caterham to enable relocating of the temperature senders away from the exhaust but I'm not sure whether it's still available. It's a known problem and I suspect is what you were experiencing.

Stu.

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Hi Stu, I completely agree with you and really appreciate the confirmation. I suspect that this was all caused by an airlock which has now either moved or disappeared.

I am still struggling to get my head around having a max reservoir tank coolant level that is below the top of the radiator and how that can work; but I suspect this it is simply a lack of experience/knowledge on my part!

I probably just need to take another look and do some more reading until I get it clear.

Thanks again. James.

 

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That's it Tom *thumb_up* Instantly turns one of the worry gauges into something useable! Better signal to teh ecu as well.

Anyone ordering one needs to also make sure they order 2 x blanking plugs that fit the threaded holes, they're needed for the coolant rail after the senders are removed.

James, I might be wrong but I'm pretty sure the level marks on the expansion tank are above the top of the radiator?

Stu.

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My radiator's not fitted in this photo, but you can see from the height of the mounts that the level marks on the expansion tank (both in the upper half) will be clearly above the top of the radiator:

7DC334E1-D575-40E8-9F8F-15B6E1F66912.jpeg.f833d7e828067b33da850719634d602a.jpeg

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Ill take a picture this evening when I get back and post it for comparison. The radiator was newly fitted when I bought the car a year or so ago, I did wonder if it had been fitted at the wrong height, but given the physical dimensions of the nose cone and the clearly defined mounts; I can't see how that can be the case. Likewise, there is only minimal clearance between the top of the reservoir and the underside of the cone.

Ill come back with some photos later on... James.

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TomB,

Your post intrigued me.  I've not seen the two outlet pipe you linked to before.  

Where is it supposed to go in the cooling circuit as the original 'submarine' pipe for K series was so called because of the side outlet ("conning tower") which connects to the expansion tank?  Presumably the pipe you show only works if it is fixed in place via the stud to ensure the temp sensors maintain their electrical connection, or some other means is employed to ensure the electrical connection is complete.  

My K series car has never 'behaved' well when it comes to the cooling circuit, which conceivably could be down to heat soak from the exhaust manifold and not a real cooling issue at all!  It has never behaved as well as my mate's 1.8K which demonstrated the sort of behaviour I hoped for and all the measures I've tried (regarding bleeding - T piece, hole in the thermostat etc) have had little beneficial effect on my 1.6K.

Ezzer

NB FWIW This post was a ‘reply’ to TomB (post #12), not #15 so why the header to this post says it’s a reply to #15 I have no idea!

 

 

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Ezzer, the part Tom has linked to is smaller than you might be thinking. The usual "submarine" fits in the bottom hose from the radiator to the thermostat (32mm ID) whereas this adapter fits in the 16mm ID top hose that runs to the heater, or if a heater isn't fitted it goes into the bypass hose running round the rear of the engine. The actual location doesn't need to be too accurate, fundamentally it just needs to be well away from the exhaust. You can see mine in the photos below in the bypass hose, mine's a gold colour rather than black (there's a name for the gold treatment but I can't remember what it is!).

If the senders have two wires they're already earthed, earlier cars had a single wire sender for the temperature gauge so needs to be earthed via the threaded section, i.e. earth the submarine tube with a wire from the threaded section to a suitable earth.

Stu.

803E8D6F-8597-4445-AD12-43337CBFEDD2.jpeg.6536b3307398ee62315d69dc1bc94fd0.jpeg
 

992DDC66-F432-4FD1-B7F1-E052C12A1E60.jpeg.491e916a9796bdb2bc792895e0a67004.jpeg

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Hi Stu,

This proved to be quite a tricky picture to line up, but hopefully the following shows the situation clearly:

Firstly, the car is on as near dead level ground as I can manage:

IMG_1670(1).JPG.98dbc00dffaa32600934668af0f53cf7.JPG

And a second level balanced across the upper most part of the radiator such that it is also as level as I can reasonably make it:

IMG_1672(1).jpg.6b44313bc6f318f904703b4f1025844a.jpg

Now (and I hope that this is clear!) the four lines on the below are (in order):

1) Upper most point of the radiator.

2) Estimated upper most water level in the radiator and top hose.

3) The Max level on the reservoir.

4) The Min level on the reservoir.

IMG_1674(1)_0.JPG.9c963bf90fd38d9b43c4829635a495d6.JPG

So, essentially, unless the coolant level is about an inch and a half higher than the max level; I don't think the radiator or top hose will ever be full?

Would value any thoughts....

James.

 

 

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Mine is an older car than yours, different radiator and different expansion tank. Your last photo shows a substantial amount of clearance between the chassis tube and the top hose, in earlier cars the hose just touches the chassis tube. Whether the radiator is taller or mounted higher would be hard to say but I can see you have a problem!

Stu.

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Every day is a school day as they say, i'm certainly learning!

I think ill just make a mark on the reservoir with what I think is the right level and run with it for a while. In reality, the only thing I have done is reduced the expansion volume by a bit which should just increase the pressure in the reservoir when hot. I am sure the car will let me know if it becomes a problem. 

Great discussion and I really appreciate all the input, many thnaks to everyone.

James.

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That's a good point - its a 2004 Roadsport SV; however when I bought it about a year ago it had had some front end damage and I think the radiator had been replaced as a result. Perhaps I have ended up with a mismatch rad/bottle which would indeed explain things.

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Hi Stu,

Thanks for the comprehensive explanation.  I may have worked it out for myself, eventually, but I much appreciate your very clear demonstration of how it goes.  Removes any doubt about how to do it for which I am grateful.  I've ordered said part from Caterham but they didn't have any plugs to fit the existing sensor locations.  They reckoned that one was 1/8" NPT and the other one was probably M12.  This has since been confirmed by Chris at Redline (who else?) so now I'm after some blanking plugs (Chris didn't have any either at the moment).  eBay to the rescue I think.

Many thanks, and to John for the remark about the 'reply bug'.

Ezzer

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