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Smiths Temp Gauge Reads Low - Spyder Zetec

PostPost by: gavk » Tue Sep 22, 2015 9:23 pm

Evening

My Spyder Zetec +2 tends to read slightly low on the coolant temperature gauge and on the fuel gauge. I had never linked the two problems until tonight and now I'm wondering if I might have a faulty voltage stabiliser.

Is there a voltage stabiliser fitted to Spyder cars and if so, is it in the same place as originally in the +2?

My fuel gauge never goes above 3/4, even when tank filled up to edge of overflow in filler neck.

My Coolant temp gauge never goes above 85degC and spends most of its time in the 60s or 70s.

I have an original looking Smiths Coolant Gauge with 85deg midpoint and orange hand.

If the VS is a red herring then alternative explanations for my low readings are:

Fuel Gauge:
Fuel gauge reads low because tank not filling fully due to high position of tank top in relation to filler neck and consequently fuel level sender may not be achieving full travel.

Temp Gauge:
1. Reads low because of mismatched gauge/sender. My sender is located in the front of my raceline water rail, not sure if this sender is a ford part and consequently mid matched to gauge?

2.Temp gauge reads low because it spends most of its time above the coolant level. The design of the raceline water rail is such that it places the temp sensor above the level of the top of the cylinder head. When the block is full of coolant, the temp sensor is still dry, its not until the thermostat opens fully that I can imagine the sensor gets to see the full coolant temp.

The raceline water rail has a few bosses for attaching sensors, and its only the front one that sits dry in my installation. My Emerald ECU has a temp sensor plumbed into the rear of the raceline water rail and I'm going to compare the readings this sees (waiting on cables so I can hook PC up to ECU and test).

If the ECU is seeing higher temps than the gauge shows then I may purchase a third sender and use the spare 'wet' boss on my water rail to see if that produces a higher gauge reading.

Also planning to take an IR reading of the temp and perhaps get one of those temp reading stickers to aid discovery of my true temp.

I had the thermostat out today and it is an 88degC stat which seems to be operating correctly and allows a small amount of coolant bypass.

Anyone with experience of this setup or thoughts on my ideas?

Many thanks

Gavin
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PostPost by: PeterK » Thu Sep 24, 2015 9:38 am

IIRC, Zetecs like to run hot, and mine sits constantly above half way on the original gauge (standard Ford sensor fitted in to the end of a Raceline water rail, pointing towards the front of the car. It took some messing about to get my expansion tank high enough so that there was always water in the water rail.

As a quick first test, if you earth out the petrol (at the tank end) and temp (at the RaceLine end) sender wires, do both gauges go to max ?
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PostPost by: gavk » Thu Sep 24, 2015 1:59 pm

Hi Peter

Yes, I've heard that the zetecs like to run hot which is why I haven't been liking the low temperature readings.

The more I think about it, I used to get a higher (more accurate) temp reading when I used to run with a higher volume of coolant. I previously would've filled the system to a point where the temp sender (above thermostat in water rail) was always submerged. The reason I stopped filling to this point was that there was not enough air in the system to allow for expansion and the system was throwing away excess coolant.

I think you are onto something thoough, my expansion tank is hinged so I may be able to raise its height slightly and add more coolant while still maintaining an acceptable quantity of air to allow for compression during pressure build up.

I tested the engine temperature last night with a Thermal Imaging Camera and it is running up to 90degC happily, just got to get the gauge to show it!

If I earth the senders as discussed, will this prove the voltage stabiliser is working correctly?

Thanks,

Gavin
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PostPost by: spyzee » Sat Oct 10, 2015 12:15 pm

Ahhh - very interesting.

When I first got the car on the road the temperature gauge was spot on (86 degrees) and matching the thermostat. This lasted for about 5 - 6 months before it started reading low (60 - 70) and certainly never reaching 85 so I replaced the thermostat. That cured it for all of 6 months when the reading dropped back to 65 ish. So I replaced the thermostat again and sure enough it was fixed again - for 5 months. So I rang Spyder and researched Raceline problems but no one was able to shed light on this "problem". So far I have put seven thermostats in this car and am at a loss to find a satisfactory explanation. The car doesn't lose water. It doesn't overheat. It's been completely rewired. I drove it in standard form for over a year and only had the problem since I did the full Spyder Zetec conversion.

Logically there only seems to be two explanations:

Either there's a national batch of faulty thermostats or the thermostats are not faulty but the act of replacing it "cures" the problem for a while.

It's just started again (2 months) so this time I'm going to take the thermostat out and put it back in again. It could just be a bit of quantum mechanics is needed.

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PostPost by: PeterK » Sat Oct 10, 2015 4:42 pm

Could there be a dodgy connection on the temp sender ?. If every time you replace the 'stat, you're moving and reconnecting the sender and all is good, then over time, corrosion builds up and gives a low reading ?

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PostPost by: Craven » Sat Oct 10, 2015 5:00 pm

You can check the thermostat function by placing it in a cooking glass bowl of water placed on a hot plate using an ordinary thermometer.
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PostPost by: Chancer » Sun Oct 11, 2015 12:29 pm

I'm going back 15 years now but I had no end of problems with a raceline water rail because the thermostat was now located in a dead spot away from its correct location at the rear of the block, before the Raceline water rail I had a cobble up of hoses but with the stat in its ford housing in the correct position, it worked fine.

The problem with the water rail was in the warm up period, the stat wouldnt open when it should and the engine overheated before it did, I do recall the indicated temperature on the guage not being correct but I have forgotten the why and how now, there was also an issue with heat from the exhaust headers heating the water rail, the car was a Caterham 7.

I eventually found the solution was to drill a 4 mm IIRC bleed hole through the flange of the thermostat to allow some circulation before the stat opened, a bit like a water pump bypass hose, try this and see if it solves your problem.

I would hope that in the intervening 15 years Raceline would have either solved the problem or advised owners of the mod but back then they made a show of being in denial to customers, "you are the only one that has ever reported this fault" etc, untrue as I had met may other owners with the same problem who were told the same thing.

In my experience companies that start down that road usually never deviate.
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PostPost by: gavk » Sat Oct 24, 2015 5:16 pm

A bit a progress in relation to my original post.

I believe the fuel gauge is right and my tank is only ever 3/4 full so we can eliminate the Voltage Stabiliser.

I have started connecting up my laptop to my Emerald ECU and comparing coolant temps on there, my ECU temps correlate quite well with my Smiths gauge.

I have since replaced my thermostat (was 88deg, now 92) and my fan switch.

I believe my old thermostat was opening too soon or letting too much fluid by. Issues never presented themselves during the warmer summer months but since the weather has become cooler my gauge was only showing approx 60deg last week after 20miles on the A3!

After fitting my new stat (theoretically only 4deg difference), my morning drive today on the A3 and the gauge came straight up to 85deg and then proceeded to cycle between an indicated 75 and 85deg as the system cycled open and closed.

I have checked the system over with the thermal image camera again and while I think my ECU and gauge are approximately 10deg down on reality, I'm happy with that.

Colin could your 6monthly reoccurring issue also be a seasonal coincidence and perhaps you have a thermostat issue like me?

For the record, I have not bothered to drill the new thermostat to allow coolant to bypass. When the thermostat is closed, the coolant seems to bypass via the heater pipework and this is enough to allow a constant but small flow of coolant.
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PostPost by: spyzee » Fri Oct 30, 2015 9:44 am

Well I've had a little development.
I first checked the height of the expansion tank but this was OK. Top of tank is just 5mm below bonnet.

I then sneaked up on the thermostat housing, undid the bolts until some water bled through, just a tablespoon's worth,and then tightened it back down. My trip to work is 61 miles - 4 miles of lanes, 40 miles of M4 motorway followed by 17 miles of lanes. So the car gets up to temperature by the time I hit the motorway. If I do 70 mph along the motorway the temp gauge sits happily at 82 all the way. Within minutes of hitting the lanes and going up and down hill the temperature range drops and varies between 55 and 70. It never hits 82 again until I pick up a constant high speed. I park up in work, open the bonnet and check the water level in the expansion tank and check the radiator. The water level has increase by about and inch but there are no cold spots on the rad.

My ECU temperature reading is about 10 degrees above the thermostat value so the thermostat is an 82, my ECU shows water temp reaching 92 before the water starts getting cooler. The radiator fans cut in when they should so I think the ECU temp sensor and the fan sensors are both working ok. This leaves me thinking that the problem is related to something in the thermostat housing as before I did the "bleeding" bit the gauge never reached 82. mmmmm.
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