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soldave

Operating temperature when driving?

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Was driving home from a car show on Sunday afternoon which was a relatively warm day by UK standards (22-24 degrees or so!). Motorway driving for around 40 minutes and a steady 65-70mph. As I'm driving along the temperature guage hovers around 90, sometimes going a needlewidth over, and sometimes dropping so that the needle is clear of the numbers, where it'll hang for a little while before going back up to 90 again. Now I've read that theses stock gauges aren't the most accurate in the world, but does that sound about right? I know if I'm stood in traffic and the gauge hits 90 then I'm turning the fans on to drop the temp a little, but when I'm on the motorway I'd have thought the airflow should be doing that if the cooling system is working right.

Only thing I could possibly think of is that the thermostat might not be moving smoothly. It's not sticking completely as the cars is keeping cool when moving, but it's the only thing I can think of.

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Also, depends on the 10V voltage regulator. Check if the fuel gauge also changes in sync with the temperature. I find this the biggest variable in my car. If you are moving at reasonable speed, even in 40+ degrees the fan isn't needed(yes, I have done it), if all else is well.

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Fuel gauge needle is rock solid and just goes towards empty a little quicker than I'd like! 😁

Any movement in the temp gauge needle is independent of any other gauges.

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I'd start by looking at the radiator and making sure it isn't (partly) blocked. Did the temperature come down once you slowed down, are stay around 90?


I have made many mistakes in my life. Buying a multiple Lotus is not one of them.

 

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In my Esprit the normal operating temperature is just below 90. In stationary traffic (yes M25, I'm meaning you) it will go up to just under 100 before the fans cut in, and then the dance of the temp gauge commences. Last year in the very warm weather the temp on the motorway at 70mph would be just over 90 degrees.

In my Excel, the normal operating temp is just above 80. Again in stationary traffic the gauge dances between 90 and 100 with the fans kicking in and out.

I don't have a manual override on either car.

If you are not aware, due to the way the water inlet and outlets are positioned on the 9xx engines you should turn your heater on, especially when you are expecting the temperature to rise i.e. in stationary traffic. This allows better water circulation to the rear two cylinders - it also has the added benefit of removing heat from the engine - although the cabin can get a bit uncomfortable.

There were a couple of times last year when I noticed a distinct drop in the gauge (in the Excel) when I turned the heater on in slow moving traffic.

I much prefer the Smiths gauges in my Esprit (1982) to the VDO ones in my Excel (1989). They are all have a much steadier reading and are larger and clearer. The VDO ones are smaller and the needle seems to bounce around on all of them.

 

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13 hours ago, Escape said:

I'd start by looking at the radiator and making sure it isn't (partly) blocked. Did the temperature come down once you slowed down, are stay around 90?

If I drop to 60-65 then the temperature will usually drop a little. If the needle being at 90 is about right then I'm not worried about slight fluctuations, but if it should be quite a bit lower on motorway runs then I'll do some more investigating, and radiator might be a good call.

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I think there is a lot of talk about over heating on the interweb which leads people to put in manual fans to reduce the temp.

IMO the fans should be controlled by the thermostat which I think is set to about 90 deg C?

This was set as an optimum level. The engine need to be warm to run well.

I think as long as the fans cut in when they need to, all should be ok.

That said if Im sat in traffic for a while when I get going mine does stumble a bit until the carbs run through a bit. I think the fuel sitting in the carbs over a hot engine heats up and loses some octane?

If I switch mine off hot and return between 10 mins and and hour or so its often takes a few cranks. Again I think this is due to the fuel heating up in the carbs. Its always started after a few turns...just be sure to have a good conditioned battery.

I did see those who change to the new high torque starter motors which require less omph seems to help.

 

buddsy

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"Belief is the enemy of knowing" - Crrow777

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2 minutes ago, Buddsy said:

I think there is a lot of talk about over heating on the interweb which leads people to put in manual fans to reduce the temp.

IMO the fans should be controlled by the thermostat which I think is set to about 90 deg C?

This was set as an optimum level. The engine need to be warm to run well.

I think as long as the fans cut in when they need to, all should be ok.

That said if Im sat in traffic for a while when I get going mine does stumble a bit until the carbs run through a bit. I think the fuel sitting in the carbs over a hot engine heats up and loses some octane?

If I switch mine off hot and return between 10 mins and and hour or so its often takes a few cranks. Again I think this is due to the fuel heating up in the carbs. Its always started after a few turns...just be sure to have a good conditioned battery.

I did see those who change to the new high torque starter motors which require less omph seems to help.

 

buddsy

Interesting what you said about the carbs getting a bit of heat soak. Mine's exactly the same taking a little more to get started after I've turned the engine off for a little while.

My fans are manual and I've no problems putting them on at 90. I think the question was more when I'm doing motorway driving, should it be getting up to 90 and needing the fans switching on at all

Appreciate the thoughts :)

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Ambient air temperature will affect engine cooling directly - the air just above the road on a still day could easily be quite a bit hotter too.

I'd have thought that if you can keep the engine from overheating then it's all under control.

Some people remove the aircon rad to restore the original (?) airflow, and a dual core modern radiator will cool better too - so we know it's a bit borderline,  and the condition of the water jacket in the block,  inside the rad and even the hoses will all be reducing cooling.

My front numberplate blocks the intake too - I'm sure it wasn't designed like that.

Alternative cooling fluids also seem popular.

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The thermostat on the Eclat is a 82° one, just like on later 9xx 4-pots. In my Esprit, I usually get a temperature reading of 80°C to 85°C, regardless of speed. And confirmed with Espritmon. Which means the thermostat is doing a good job of controlling coolant flow though the rad right around it's working point. Only when stuck in traffic will temperature rise, until the fans come on around 90°C and bring temperature back down. So I wouldn't be comfortable running at a constant 90°C. That said, you might want to check the reading, as accuracy can be off.

For the record, I do have a manual override fitted for the fans, in parallel with the standard ECM control. So no risk if I don't turn them on manually, but I often do so just before parking, as that usually means slow traffic and I feel better parking the Esprit with the temperature not around/above 90°C.

Dave, if a slight reduction in speed sees the temperature drop, I'd say your cooling system is at its limit. So airflow or coolant flow or both could be below spec. At constant motorway speeds, you're not really pushing the engine, so should have a fair margin. Radiator is relatively easy to check/clean/flush, thermostats are cheap, piece of mind when enjoying our wonderfull cars is priceless. 😉

Filip


I have made many mistakes in my life. Buying a multiple Lotus is not one of them.

 

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Thanks guys for your thoughts. I'll probably try replacing the thermostat first off, so will get one and a gasket ordered in the next day or two. Got a trip to London planned early next week so will change it after that - don't want to risk taking anything apart before then as even the simplest jobs end up being much more complex than I plan!

if the thermostat checks out OK I'll make plans to test the radiator flow.

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Wanted to tie this off so wrote a little about it in my project thread here:

 

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Some people have left out the deflector that fits between the fans and the engine, it guides the air over the top of the engine and out of the slats in the bonnet. If this is missing you will get overheating. Also check that the otter switch is not playing up.

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I'd probably say the majority don't use the cooling panel before. I had it installed although have removed it whilst I'm doing the testing for my new fan wiring. If all goes well then it may go back in :)

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Hmmm. High temps at motor way driving or fluctuations may point to water pump issues. There is a critical distance that the impeller needs to be from the back plate of the pump to make the flow rates. From memory, the impeller and shaft are just pressed in place so the shaft can move although you would normally expect to see a weep from the tell tale hole.

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7 hours ago, Drawfiler said:

Some people have left out the deflector that fits between the fans and the engine, it guides the air over the top of the engine and out of the slats in the bonnet. If this is missing you will get overheating

Not in my experience.

Drove up Highway in Austrslia, in 38-40degC at 110kph or slower, had a manual overide and never a problem. elite 502

In UK, done some long trips, 60-70mph, again, no problem. Have a cover, but not fitted at the moment, and doesn't seem to be an issue. Elite S2

I would look for other reasons if overheating.

 

 

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3 hours ago, Clive59 said:

Not in my experience.

Drove up Highway in Austrslia, in 38-40degC at 110kph or slower, had a manual overide and never a problem. elite 502

In UK, done some long trips, 60-70mph, again, no problem. Have a cover, but not fitted at the moment, and doesn't seem to be an issue. Elite S2

I would look for other reasons if overheating.

 

 

I have had the deflector in and out and I agree that it doesn't make a lot of difference to cooling but I did notice that it keeps rain water from running down the bonnet vent and over the front pulleys....well mostly! (I added a small deflector under the vent)

Not a problem if your car lives in a garage, but a major problem if your cam belt adjuster bearing gets wet rusts and seizes. 

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It's got a summer thermostat in it I think it's 82° original radiator and I'll show you a picture of its normal running

image.jpeg

 Wife took the picture this morning that's why it's wonky but if it's sitting ticking over and you're not moving the fans cutting at 90 and it goes from 90 to 80 well ticking over cheers bye 

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Standard thermostat is 82°C, so you're running right on spec.

Hot climates had a (optional?) 74°C thermostat.

Filip


I have made many mistakes in my life. Buying a multiple Lotus is not one of them.

 

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