Engine over-cooling

[taylormj4]

All,
In these low temperatures, the Chimaera typically never reaches even 60deg when running. My understanding is that low temperature running is not good for the engine - crud build up and lower efficiency. Plus the heater output is poor.

Modern cars seem to reach 90deg and sit there quite happily regardless of road speed or ambient temperatures.

Is the problem on the Chimaera that the thermostat doesn't have enough control over the cooling system or is it that the engine bay has too much inherent cooling via the bonnet vents ?

Anyone managed to get better control over the engine temperature ?

Cheer, Matt

[taylormj4]

QBee said:

Have you not noticed how your Audi, BMW, Mercedes, Saab, Lexus, whatever goes up to 90 degrees almost straight away and stays exactly there whether it be 3 degrees or 30 outside, and motorway or traffic jam?
A 21st century car's temperature gauge has only got three positions - off, fine or fked.
It's only purpose is to tell you that much.

Well, I thought this too on our Audi A4 and assumed the same. However, it started showing lower temperatures and the temperature dropped at motorway speeds, much like the TVR. When this was investigated, the thermostat was found to be faulty and after it was replaced, the temp comes gradually up to 90 and then stays there. So I think it is accurately reading the temperature, the system is just better at controlling the temp. I think modern heater systems probably need a more consistent hot water input for these climate control systems.

[taylormj4]

PhilH42 said:

Even in this cold weather mine still runs as always (well since I sorted out the cooling system) which is 70-90 dependant on driving conditions/traffic. It may take a little longer to warm up but no real difference, so it sounds like something's not quite right. I'm presuming the gauge and sender have worked - at least as accurately as can be expected in the warmer weather and theres no overfueling? Well no more than on warm up.

Think everything is working correctly, yes. At least, it's always behaved like this. In the Summer, the temp comes up to 70-80 whilst moving and go up to 90-95 in traffic with the fans cutting in/out correctly.

In Winter, the temp will come up to around 60-65 but when moving it drops to 50-60.

The heater output temperature matches the gauge so when the gauge reads lower, the output heat from the blower vents is cooler, so I think the gauge is accurately showing the coolant temperature.

The only time this hasn't happened is when I had a minor un-noticed coolant leak and the level had dropped significantly. The coolant temperature was a lot higher for the time of year and eventually the heater output went completely cold, even though the gauge was showing hot.

So I am confident that the gauges are reading accurately.

My first thought was that the thermostat was stuck open but others were reporting the same behaviour from their cars so I thought this was just normal.

[taylormj4]

bobfather said:

You sound like you're the first person to have this problem, you are not. Your dash gauge is not reading correctly and the fix is simple. I've done the Rover sender mod on 4 PH members cars to date, all of them suffering the same symptoms that you describe. All those gauges read correctly now, you'll also be amazed how quickly the engine reaches full temperature.

The TVR sender is in a very poor location and suffers from poor coolant flow and massive air cooling. Sometimes my gauge wouldn't rise at all until I stopped or slowed down. The RoverGauge reading showed me that the engine was heating up quickly and stably winter and summer. The ECU sender is well located, the TVR sender is poorly located. Many owners have seen precisely what you observe, the solution is very simple, carry out the Rover sender mod then thank me for being persistent

Bobfather, I understand what you're saying and agree that the gauge could be sited poorly and exhibit those conditions but my point is this: if the gauge is reading incorrectly low and the coolant is actually at a much higher temperature, why does the temperature of the air output from the heater go cooler when the gauge drops ? Surely if the coolant was actually hot (as you suggest), the heater output would remain high. My experience is that the heater output temperature (which is linked to coolant temperature) matches the temperature gauge. That suggests the gauge is reading correctly.

[taylormj4]

BeastMaster said:

Mine is exactly the same.

During the very cold months I insert a blanking panel in the middle of the rad, which covers a portion of each fan to cut down the cold air blast. This allows the temp to be similar to summer months and increases the heater output. In traffic the temp is the same as summer, less air is sucked through the rad but it is colder.

Very high performance cars have this type of thing auto operated, mainly to decrease drag, did think of making a mechanical operator, or even an electrical system running off water temp, but sticking a blanking piece in seemed much more TVR.

Andy.

Thanks Andy, glad to hear it's not just me. I actually trial fitted a piece of thick cardboard in the centre, thinking that it would allow each fan to pull through as you said. It pinged into the slot between the body and the bottom of the rad and then snapped into place behind the air filter. Then I thought about the mess it would make if I drove in the rain ! So now, I'm thinking thin perspex or something similar.

[taylormj4]

ClassiChimi said:

I used to own a series 3 XJ6
That had rubber flaps on the rear of the rad housing, over a given speed the wind would push them away and allow the air through

Interesting idea but wouldn't that mean it would overheat in traffic?

[taylormj4]

bobfather said:

Very simple answer.

The heater matrix on full heat increases the temperature of air flowing through it by a set amount, say it adds 20degC.

If the outside air is 22degC, the heated air will be 22 + 20 so the hot air into the car will be 42degC.

If the outside air is 5degC, the heated air will be 5 + 20 so the hot air into the car will be 25degC.

Interesting, but the air termperature doesn't change much on a single day on a short journey.
So, again, if you are sitting in traffic and the temp gauge is reading say 70C, the air output of the heater is hot. Then when you get up to say 40mph, the temp gauge drops to 55C, the heater output drops to warm. That cannot be attributed to ambient air temp changes.
You are saying that the gauge is wrong and the coolant hasn't actually dropped in temp, it's just the gauge.
What I am saying is, the coolant temperature has dropped, so the gauge is correct and does reflect what is happening with the coolant temperature.

I agree that the gauge may not quite be calibrated correctly so say 55 is actual 60 and 90 is actually 95 but it's not far out.

I think the comments from others on the thermostat opening temp is probably the answer here and the noe fitted is too low.

[taylormj4]

FoxTVR430 said:

Taylormj4
Maybe it's a case of your thermostat sticking open, or not being there at all!
As others have said, the thermostat is there to help get your engine up to temp ASAP.

But suppose it is always open. Then the car would generally take longer to warm up.
As you drive along on these cold winter days the cold air flow through the radiator will cool the engine water temp down as the thermostaat will not shut the flow of water to the radiator. Thus making the whole water system cooler.
As you said your temp gauge is working and showing the drop in water temp, the air feels cooler from the heater, etc..

But when in traffic the engine water temp would rise to the temp that the otter switch would turn on the fans. The fans would draw cool air through the radiator cooling the water until the otter switch turned them off. The thermostat will always be open in these conditions.

Indeed. A temporary fix for poor cooling on an engine used to be to remove your thermostat so that it ran at lower temperatures and gave you a bigger buffer for when you got stopped in traffic. However, on some cars, the thermostat forms a seal between the pipes so if you remove it, the coolant leaks out, as I found on an old Rover in my youth! I plan to check the stat condition asap.

[taylormj4]

cureton said:

Dave, thanks for your early morning comment, fully agree, this was my understanding so far as well. But still asking myself: When the thermostat is fully open at a certain temperature, lets say 88°C ,it allows full waterflow through the rad. It then leaves things fully to the cooling system to keep the 88°, avoiding overheat in traffic by support of fans.The cooling system and its capacity was designed to work under certain conditions including outside temperature so ist fully up to the Job even in hot summer. But if the ambient temperature is a lot lower like in winter, the capacity of the cooling system is too large so the water temperature may drop significantly below the 88°. But shouldn't the thermostat come into play then by gradually closing and therefore reducing waterflow through the rad to allow a "comfy" temperature of the water circulating in the engine? As you say the stat doesn't snap open, it would also not snap shut I guess. It just strikes me that you would have to limit the airflow through the rad by whatever material to avoid overcooling instead of leaving that job to the stat? Or maybe I'm thinking the wrong way.

That is my understanding. The thermostat used to have a little wax cylinder in it that responded to the water temperature flowing past it by applying force against the spring. It is an analogue system and does not snap open or shut. Similar thermostats exist in mixer showers. When the stat starts to open, it will get a big blast of cold water that has been sitting in the radiator, which will cause it to close again, then when the engine heats up that water, it will start to open again. Gradually the temperature in the radiator and engine will stabilise and there won't be the big shock changes in temperature of water coming in from the radiator (expcept when the fans cut in) and the stat will find a position that matches that.

The thing that the stat can't control is the cooling effect of the air rushing under the engine and up through the engine bay due to the forward movement of the car. That cools the block of the engine itself. If that effect is significant enough, and the engine is only at small throttle opening (cruising) it is possible that even a completely shut thermostat could not stop the temperature of the engine coolant from dropping. This was part of my question.