Engine overheating when idling.

[GreenGoddess]

Hi guys

 

I’ve had overheating problems with my car (84 Turbo) since I bought it last year. Initially I think it was an airlock that was causing the problems. I changed the coolant temp sensor, checked the fans were in working order, replaced the header tank which was leaking and flushed and renewed the coolant. 
 

The temp gauge now stays consistently at just below 90 degrees all the time when driving. However, if I get out of the car when it’s fully warmed up and leave the engine idling for a couple of minutes then the temperature keeps rising until it gets worryingly high. The fans do not seem to come on so I manually turn them on by putting the AC on full. I also turn the heater control to hot. But the temperature gauge still keeps rising. 
 

I know what you’re thinking. The otter switch! But I don’t think that is the problem. When I get back in the car and drive off, the temperature will stay high until I select a low gear and keep driving with the engine revs higher than normal. Then the temperature drops quickly until it’s normal again. 
 

So I’m thinking that the problem has something to do with the circulation of the coolant. It’s as if the water pump isn’t working hard enough to get the coolant to flow through the system to the radiator and back. The otter switch will only trigger the fans if the water flowing past the switch is hot enough. I think all the hot water is remaining concentrated around the engine until I get the revs up enough to circulate it properly. 
 

What do you think? Any ideas?

[jonwat]

14 hours ago, GreenGoddess said:

What do you think? Any ideas?

Are you sure the belt is tight enough & not slipping? 

[Escape]

Your theory is sound, a worn water pump or slipping belt can mean coolant flow is insufficient al low revs. But before going in there, do make sure the fans are actually coming on.

Turning on the AC might not be much help: if it is working, the fans should come on, but the condensor will also add heat to the radiator pack. If it's not working because of low pressure, the low pressure cut-out will not only disable the compressor but also the fan override.

Finally, a (partly) clogged radiator will also prevent flow, especially at low revs, and be less able to dissipate heat.

[ChrisJ]

I've been advised by my mechanic that when idling - sitting in traffic or similar, to up the revs slightly (700 -> 1000) to give the water pump a bit more oomph as it's a long way from the rear to the front. 

Although my fans definitely come on and the temps go back down - as you can watch the temp gauge do the dance.

[Chillidoggy]

You said yourself that, “the fans do not seem to come on.”

I’d be changing the otter switch first.

 

[GreenGoddess]

8 hours ago, jonwat said:

Are you sure the belt is tight enough & not slipping? 

That is something I will need to check. That would be a nice easy fix!

7 hours ago, Escape said:

Your theory is sound, a worn water pump or slipping belt can mean coolant flow is insufficient al low revs. But before going in there, do make sure the fans are actually coming on.

Turning on the AC might not be much help: if it is working, the fans should come on, but the condensor will also add heat to the radiator pack. If it's not working because of low pressure, the low pressure cut-out will not only disable the compressor but also the fan override.

Finally, a (partly) clogged radiator will also prevent flow, especially at low revs, and be less able to dissipate heat.

Thanks. The radiator looks brand new (shiny aluminium). It must have been installed just before I bought the car. Good tip about the AC fans.

2 hours ago, Chillidoggy said:

You said yourself that, “the fans do not seem to come on.”

I’d be changing the otter switch first.

 

Yeah, I'm still not convinced it's the otter switch. When I short the wires the fans come on just fine and turning on the AC fans doesn't bring the temperature down at all. I'm thinking that the water reaching the switch is not hot enough to trigger the fans. The otter switch on my car is on the top of the pipe. Later cars had the switch moved to the bottom to avoid troubles with air gaps I believe. I suppose for the price of a switch I could just replace it and turn the pipe 180 degrees while I'm there.

Failing that, the only 3 things I can think would cause this problem is:
1. Slack water pump belt

2. Faulty water pump (sounds unlikely)
3. Thermostat not opening fully causing a partial restriction

Other ideas welcome.  

[Escape]

If you start the car and let her idle with the AC on, you should be able to confirm if the fans come on or not. You could do the same after a run (with everything up to temperature), instead of turning off straight away, let her idle a bit and see if the fans come on or not. I'm not a fan of letting an engine (any engine) idle without a good reason, so better to have an enjoyable drive to get things up to temp and then do the test rather than start the engine and just wait. 😉

[GreenGoddess]

53 minutes ago, Escape said:

If you start the car and let her idle with the AC on, you should be able to confirm if the fans come on or not. You could do the same after a run (with everything up to temperature), instead of turning off straight away, let her idle a bit and see if the fans come on or not. I'm not a fan of letting an engine (any engine) idle without a good reason, so better to have an enjoyable drive to get things up to temp and then do the test rather than start the engine and just wait. 😉

I am still mystified at how the AC works. The AC on my car seems to go through the motions but it doesn't blow any cold air (no idea why). When the car sits idling and starts to overheat, turning the AC on full always makes the fans come on. But it doesn't stop the temperature gauge rising. It just continues to rise until I get scared and switch off the engine. That's what makes me think the problem has something to do with coolant circulation. If the fans are going full tilt and the engine temp is still rising then I am assuming that the coolant isn't being circulated through the radiator at a rate quick enough to make a difference. 

[drdoom]

Correct as far as your assessment of the fans effect, and I'm curious in regard to the A/C situation. First point to check is whether the A/C clutch does indeed engage when the system appears activated. If so then why no cooling air? Is the rad/condenser array rather obstructed by debris? Might do to feel the various coolant hoses for differences in temperature when in the idling state, in order to confirm the coolant is fully present and not low. it's quite possible the water pump has been worked on while in the hands of the PO, perhaps not properly done. Slack belts typically squeal when the accessorry is spun up under load, though the pump alone should not present substantial load while the alternator certainly will. Keen to see you through on this.  

[GreenGoddess]

14 minutes ago, drdoom said:

First point to check is whether the A/C clutch does indeed engage when the system appears activated. If so then why no cooling air? Is the rad/condenser array rather obstructed by debris? Might do to feel the various coolant hoses for differences in temperature when in the idling state, in order to confirm the coolant is fully present and not low. 

I haven't bothered investigating the lack of cool air from the AC yet. When I turn on the AC I can hear a definite audible click which I assume is the clutch engaging. The radiator etc is completely clear of debris (the aluminium radiator looks brand new). 
When you say "feel the various coolant hoses for differences in temperature when in the idling state", are you talking about engine coolant or AC coolant? 

[drdoom]

Engine coolant. It's a simple but quite effective way by which to explore whether there may be a coolant level issue.

[GreenGoddess]

Thanks. I’ll do that. I assume the radiator top hose should be cooler than the bottom hose? 

[Escape]

Yes, but not by too much of a difference. If there is indeed very limited flow, the coolant will sit in the radiator and get the time to cool down a lot, so the return hose will be cool, just not enough coolant will make it to the engine to actually keep temperature down. If you have an IR temp gun that will yield some useful info. And be safer than touching coolant hoses that could be up to 100°C. 😉

[drdoom]

I'd be looking at the hoses in the engine bay first, as a low coolant level is most evident at a high point in the system.

[GreenGoddess]

4 hours ago, drdoom said:

I'd be looking at the hoses in the engine bay first, as a low coolant level is most evident at a high point in the system.

Not sure what you mean by this. What should I be checking the engine bay hoses for? 

[drdoom]

If the car has been run long enough to be up to temperature one can check that the engine area hoses are reflecting the expected heat. For example, if the hose uppermost where coolant emerges from the head is not significantly hotter than one returning from the rad I'd suspect coolant was lacking in the upper reaches of the system. It's just one more rudimentary method of examining the state of things.

Cheers

[GreenGoddess]

11 hours ago, drdoom said:

If the car has been run long enough to be up to temperature one can check that the engine area hoses are reflecting the expected heat. For example, if the hose uppermost where coolant emerges from the head is not significantly hotter than one returning from the rad I'd suspect coolant was lacking in the upper reaches of the system. It's just one more rudimentary method of examining the state of things.

Cheers

Ah, ok. I understand. Thank you. 😊

[snowrx]

Job one is getting the fans back on an automatic switch. A simple circuit and much easier to fix than a head gasket job from over-heating!

The thermostat is an easy swap to rule out weirdness there.

Do your fans have a proper shroud between them and the radiator core? Seems odd that on-road airflow will cool but the fans will not. Also confirm visually that all the fans are coming on, not just one or two. Is it possible that the new radiator came with a new fan set-up not up to the task? (pushers rather than pullers/mis-wired/undersized/etc) 

Several owners have posted pic's of nasty accumulations of road debris lodged between the radiator and condenser, but I would think that would manifest itself under load as well.

[GreenGoddess]

2 hours ago, snowrx said:

Job one is getting the fans back on an automatic switch. A simple circuit and much easier to fix than a head gasket job from over-heating!

The thermostat is an easy swap to rule out weirdness there.

Do your fans have a proper shroud between them and the radiator core? Seems odd that on-road airflow will cool but the fans will not. Also confirm visually that all the fans are coming on, not just one or two. Is it possible that the new radiator came with a new fan set-up not up to the task? (pushers rather than pullers/mis-wired/undersized/etc) 

Several owners have posted pic's of nasty accumulations of road debris lodged between the radiator and condenser, but I would think that would manifest itself under load as well.

Interesting that you say the thermostat is an easy swap. I’ve been led to believe that it’s a nightmare to get at. 😂

The fans on my radiator are the original fans. They have the proper shroud and fire up perfectly when I bridge the terminals at the otter switch. 
 

Natural airflow did not seem to bring down the temperature. Only when I changed down to a low gear to bring up the engine speed did the temperature come down rapidly. That’s what leads me to believe it’s a water pump or coolant restriction problem. Assuming the belt isn’t slack, my money is on the thermostat. 

[TAR]

1 hour ago, GreenGoddess said:

Interesting that you say the thermostat is an easy swap. I’ve been led to believe that it’s a nightmare to get at. 😂

The thermostat has been obsolete for years and an original is pretty much unobtainable. Replacements can be occasionally be found but usually have a different size pipe fitting meaning you'll need a reducer. 

It's not too bad for access

[drdoom]

1 hour ago, GreenGoddess said:

Interesting that you say the thermostat is an easy swap. I’ve been led to believe that it’s a nightmare to get at. 😂

The fans on my radiator are the original fans. They have the proper shroud and fire up perfectly when I bridge the terminals at the otter switch. 
 

Natural airflow did not seem to bring down the temperature. Only when I changed down to a low gear to bring up the engine speed did the temperature come down rapidly. That’s what leads me to believe it’s a water pump or coolant restriction problem. Assuming the belt isn’t slack, my money is on the thermostat. 

I've bold highlighted your observation on revs vs temperature because that has been characteristic of low coolant level in my experience on other types of car. Seems the churn of a faster spinning water pump throws hot coolant up where it is not present under sedate conditions. How does the cabin heater output feel?

[GreenGoddess]

1 hour ago, TAR said:

The thermostat has been obsolete for years and an original is pretty much unobtainable. Replacements can be occasionally be found but usually have a different size pipe fitting meaning you'll need a reducer. 

It's not too bad for access

Lotusbits have started selling new replacements. Apparently they’re very good. Not sure about pipe sizes but they’re supposed to be a direct replacement. See here: https://lotusbits.com/product/product-175/

1 hour ago, drdoom said:

I've bold highlighted your observation on revs vs temperature because that has been characteristic of low coolant level in my experience on other types of car. Seems the churn of a faster spinning water pump throws hot coolant up where it is not present under sedate conditions. How does the cabin heater output feel?

Thanks. That’s interesting but I’m fairly certain the coolant level is perfect with no airlocks. Heater output seems ok to me. 

[semi42]

I’m not familiar with A/C cars but when I got my S2, the smaller heater hoses and hose to the expansion filler tank were plumbed in wrong . I think it was maybe causing a conflict in flow somewhere . 

[Escape]

Have you had a chance to verify all fans come on? Either with the AC turned on or because the Otter switch closes at higher temperature. That is the basis to investigate further.

[Chillidoggy]

You’ve “bridged the otter switch”. So, you know the fans work when you do that, but it doesn’t prove the switch is working.

I’d be starting with the easy stuff first.