Cooling issues on 92 SE

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MetBlue
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Cooling issues on 92 SE

Post by MetBlue »

Need some guidance please on how the twin cap header / expansion tank works. My system definitely isn't working correctly. Not helped by my work shop manual only dealing with the single tank system😢. I think I've got several issues.

Noticed recently the temperature gauge going up towards the red when driving around town (never got there, but definitely getting hotter). Back on drive, left to tick over and fans do not appear to be cutting in as temp gauge rises (only let it get to about 100 deg on the gauge, but would expect fans running by this point.
Also Owners Manual says at least one fan comes on when AC is switched on - and it's not.

Left it over night, (as owners manual says not to remove caps when hot in case of upsetting the pressure balance of the system!!) and removed caps this morning. Front cap (header tank) fairly full, maybe an inch from full. Rear (expansion) was as good as empty. And very rusty inside. Went for a shortish drive. On return, left ticking over and quite soon, gauge was back around the 100 /110 Mark and noticed water was trickling out from the pressure relief on the front cap.
Obviously didn't remove either cap with a hot engine, but I got the feeling water could not get to the expansion tank, so it needed somewhere to go. Switched off and let cool down.
Whilst cooling, put 12 v to each fan. N/S is good. O/S don't work, so that's another problem to fix. Will be checking fuses and relays next.

But what's going on with water weeping from the front filler cap?

Tony
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Anthony
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Re: Cooling issues on 92 SE

Post by Anthony »

My fans cut in at around 90° on my 88SE. There is a temperature switch in the pipework above the rad which control's the fans. Both should run. Check connectors on temperature switch. I think you can bypass the switch by making a circuit to test it.

On the rad tank the first chamber is where you top up the water level and the second chamber is for expansion only. The water could be weeping from front filler cap because its getting too hot and is releasing the pressure.

When I first purchased mine the switch wasn't working and had been bypassed, therefore the fan's were running all the time.

Anthony

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Lotus-e-Clan
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Re: Cooling issues on 92 SE

Post by Lotus-e-Clan »

You either need to sort out your otter switch and/or relay or maybe replace the otter with a modern electronic fan stat.

I have an inline RevoTech fan stat fitted to the Excel - but it is now showing signs of flaky behavior. They cost about £70 to replace :shock: so I opted for a cheaper clone off eBay for £23. They come in all sorts of hose size - do an eBay search.

I have this one fitted to the Clan - eBay fan stat switch @ £23. A bit Heath Robinson- looking but works well. It has a good hysteresis range and compares favourably to the more expensive RevoTech (£70+!!) too. Mine is set to come on at 88C and goes off @ 78C. 78C is where both my Excel and Clan normally operate once on the move- easy to set this slightly lower operating temperature (std = 82C) because I run EWP80's on both cars (and they are both Evans Waterless mules).

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Re: Cooling issues on 92 SE

Post by Pete Boole »

The two-in-one tank gives a constant, and higher, head of coolant to the engine, resulting in better steam venting. The two sides of the tank are joined by a dip-tube which goes from the bottom of the overflow (expansion) side to the top of the other - permanently-full - side. As the engine heats, expansion causes coolant to flow from the permanently-full side, via the internal tube, to the expansion side. The reverse happens as the engine cools - coolant is sucked back into the permanently-full side by the contraction of the coolant. When the engine is cold there should still be enough coolant in the expansion side to cover the dip-tube - otherwise air is drawn in. The cap on the permanently-full side is not a pressure cap - it should constantly seal this chamber. The safety (pressure) cap is on the expansion side.

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Re: Cooling issues on 92 SE

Post by MetBlue »

Thanks Pete. Very useful. I always like to understand how and why something works. Helps understand faults.
I've got a pressure cap on both sides. Is the non pressure cap just a lid with seal to top face, or is seal face still 1/2" down, but just no spring? Cap on expansion tank is larger and I've never seen on like it before. Front tank cap just looks normal.
Tony
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Re: Cooling issues on 92 SE

Post by Lotus-e-Clan »

Ignore the blurb in picture below it is one of a set I posted to show how to convert to an EWP many years ago when this forum just got started.

The point of using the picture in this post is just to show the two expansion cap types. Just to clarify Pete's post further. I have a pressure cap (10 lb IIRC) on the full front chamber and a plain large cap on the rear expansion compartment. This is std for an SE. The hot water expansion lifts the pressure cap to expose the link tube within the neck of the front (full) chamber which flows into the rear expansion chamber. The overflow to the outside world is from the rear expansion cap neck. During cool-down the pressure cap remains open and draws exactly the same volume of coolant back until the pressure drops below 10 psi. I keep my rear Expansion chamber half full and it never overflows.

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AndyD
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Re: Cooling issues on 92 SE

Post by AndyD »

Some more background here Tony.

https://www.lotusexcel.co.uk/technical/ ... ader-tanks

Andy

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Re: Cooling issues on 92 SE

Post by MetBlue »

Would appear the tank related issues are at least understood.
I have (had) pressure relief caps on both positions ( 110KPa on large rear, no rating on front, but spring feels a lot lighter than the rear). So a simple blanking Cap ordered for the front position.

Question : Did early variants of the expansion tank system use pressure relief caps on both positions? I've read the bit posted by Lotus-e-clan earlier, but my bleed pipe definitely is open to water overflow all the while.

The bleed pipe seems clear, but there is a reasonable amount of sludgy stuff in the bottom of the expansion tank, so removal and flush out would seem in order. I doubt if the expansion tank was full at the time water started leaking from the front cap, but possible the pressure just built up until the front cap bypassed.

Still looking for a sensibly priced fan motor. There is a Ford one fitted that is working, so I might search that part number. SJ want around £150 with VAT for a new one, which I find a bit rich for a simple motor. Maybe another trip to LB beckons.
Haven't yet delved into the electrics and why the good fan isn't running even with A/c switch on. I haven't been getting a Fan warning light though, so not sure any of the electrics related to fans are actually live !

I'm tempted by the electronic fan stats. Presumably, these pretty much replace the wiring in the car (relays etc) ? so could be easiest fix for now. Given the importance of having confidence in the cooling system, I wonder about a digital temp read out to put in the car somewhere. I must say I'm not completely confident in anything the VDO gauges are telling me, but maybe I'm just paranoid.
Tony
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Lotus-e-Clan
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Re: Cooling issues on 92 SE

Post by Lotus-e-Clan »

Mine is a 89SE - essentially the beginning of the later spec cars. Not much changed after 89.

I bought my 2 owner Excel with 38K on the clock twenty two years ago. The header tank caps are entirely original OEM. The FRONT cap is the pressure relief variant. The rear cap is PLAIN (and of a larger diameter than the front).

It makes no sense to have two pressure relief caps.

It also make no sense to have a plain cap on the front and a pressure relief cap on the rear.

Think about it - plain on front, relief on rear. With a pressure cap on the rear (plain on the front) the water pressure building within the main system now DIRECTLY presses on (relies on) AIR within the rear chamber to raise the pressure relief valve (assuming the rear tank is only half full) . Air is compressible, water is not. Essentially you want the pressure relief valve resisting non-compressible water pressure within the first tank to stand a chance of proper consistent water transfer to and fro between the two tanks. Otherwise, governed by air under pressure in the second tank you will force AIR out of the second (rear) tank at 10 psi then create negative pressure (vacuum) in the second tank as the engine cools and the relief cap closes. The relief valve in the second tank will re-seat according to falling air pressure in the second tank against variable atmospheric pressure on the outside.
Last edited by Lotus-e-Clan on Sun Jul 19, 2020 22:45, edited 1 time in total.
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Re: Cooling issues on 92 SE

Post by KLM »

Hi

I had issues with my 90se cooling system a few weeks ago where I had same issues as yourself and thought it was a circulation problem, so yes header tank was bubbling over/temp gauge high and fans not kicking in.

I had the rad tested and I checked the water pump with a boroscope type device to my mobile ect. it was nothing other than bleeding the system correctly.

I have the service manual and followed it to the letter but it didn't work. eventually I got it to work perfectly (fans came on at 90c and the cooling system was perfect)

until a few days ago when I went to check the coolant level, all I did was remove the front cap and put it back on, the level was ok but next time I ran the car the fans didn't kick in again.

so firstly the otter switch can be EITHER horizontal or terminals pointing down, mine initially was horizontal but this time I changed it so that the sensor is at the bottom of the pipe(terminals down).

To bleed my car successfully I do the following.

raise the front end, set heaters to vent and max, take off front cap, start car and whilst it warms up rev it up to 2000/3000 a few times, go around and squeeze the rad pipes, yes some coolant will spill out, I saw plenty of bubbles coming out, once I couldn't get anymore bubbles I put cap back on and turned the heaters off so it reached 90c quicker, and the fans kicked in on 90c again.

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Re: Cooling issues on 92 SE

Post by MetBlue »

Thermodynamics was never my strong subject at college, and now my heads hurting trying to understand this.

My owners manual describes the system and states "the header tank, front section, is fitted with a (blank) filler cap, where as the expansion tank uses a larger diameter 110 KPa pressure cap". Our friendly fleabay describes 'blank caps' as being used on expansion tank systems, with Capri's regularly getting a mention. The cap is a simple twist and seal. No spring.

Enough other areas to fault find anyway whilst a Blanking Cap is delivered, so for now I'll let my poor little brain have a break.

Thanks all for input on this. I'm learning a lot.
Tony
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Re: Cooling issues on 92 SE

Post by Lotus-e-Clan »

One other significant thing to consider.

If the link tube between the two chambers is blocked then the first chamber will over-pressurise and eventually leak. These tubes tend to block if you don't have fluid in both chambers at all times ..or the first chamber isn't completely filled.

It's a bounder to unblock too ... :)
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Re: Cooling issues on 92 SE

Post by DavidOliver »

Sludge in the reservoir suggests radiator full flushing.
Merlin Motorsports have a good range of Radiator fans and auxilliaries.
While at it, how about removing and checking the coolant pump, check the head for a smooth water passage.


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Re: Cooling issues on 92 SE

Post by rbgosling »

I found a very affordable replacement for the Otter switch on eBay that is still working fine, details here.

Always worth checking if the temperature gauge is giving you an accurate reading (although your other symptoms suggest it is getting hot, and in-town driving in the recent weather would make it unsurprising). You're welcome to pop over and borrow my infrared thermometer, alternatively they are really not expensive on eBay.

I have the very common Ford replacement fan on one side. It's apparently from a Fiesta, but I have no idea what version so that's limited help! It's a shame we no longer seem to have the old-style scrap yards where you could wander round and grab bits off a car (before trying to negotiate with the overweight chain-smoking owner in a portakabin by the gate, and his unpleasant dog!).
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Re: Cooling issues on 92 SE

Post by CHRISYD »

Make sure the fan switch (otter) is the correct way up. I think the wires should be at the top or side on.
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