P38 Heating

[Drakes]

Had a strange journey yesterday. Was travelling down the A1 with the heating set at 21 degrees and all was fine untill we slowed for a roundabout, as we left the roundabout the heater started pumping out cold air. So we turned the heater up to 24 and straight away hot air starts to blow so we turned it back down to 21 and all was fine again untill the next roundabout. The same thing happened when we slowed for road works.

ANY ideas that may help would be greatly appreciated.

I have check water levels as this was my first thought but it is bang on the line and temperature gauge shows normal and no warnings come up on dashboard.

We had travelled down from Scotland doing about 500 miles with outside temps ranging from -7 to +5 according to the gauge which I think must be about right as the washers and wipers were freezing even with plenty of screen wash added.

Thanks Keith

[David Sparkes]

I'd still think low coolant level. How did the heater work first thing this morning, after an overnight stand?

If you checked the level while the engine was hot I'd expect it to be over the level mark, so on the mark would be a bit low.

I don't run the V8 myself, so cannot quote how much the level varies.

Cheers.

[Ally V8]

I'm with David on this,however you look at it there are all the classic signs of low coolant level.This is esp common on DII TD5's when they suffer coolant loss from the early stages of head gasket failure.There are many possibilities for coolant loss other than head gasket,but as the water pump slows with engine rpm,there simply isnt enough "slosh" of coolant to push it around the heater matrix.There is also not really any sensible explanation as to how the Hevac ecu could play up in the way that it would shut down the blend motors to the cold position as the car slowed down.

Is the coolant actually at the level or is the inside of the header tank stained to that level ?

[Drakes]

Check coolant again today and still ok, but when I fisrt det off in the car the heater was just getting hotter and hotter and so had to turn it right down to 17 then it settled and turned it back up to 21 and all ok untill I slowed down again.

I don't know but as revs drop would voltage from alternator drop and could that efffect HEVAC

[David Sparkes]

This gets interesting, although that might not be your description!

Let's go back to basics for a moment:

Which engine is this?

What year is the car?

How many miles overall, and while in your ownership?

Any recent work on the engine or car, either for you, or reported by the previous owner?

Without going into detail, no I don't think a failing alternator will cause the HEVAC to give the symptoms you are reporting.

Cheers

[Ally V8]

It would appear that the only way forward with this now is to get the car on Testbook and see what sensor inputs the Hevac ecu is seeing.Fault codes on LP Hevac ecu's log at the twist of a blade of grass so they really need clearing and testing to see what comes back.As David said it would help to know what engine your car has and if its a v8 does it have LPG ?

[Drakes]

4.6 on LPG

130000 miles of which I have done 70000.

The LPG is an AG multipoint system which I had fitted when I bought motor.

1998 one of the last GEMS engines, chipped by Mark Adams

[David Sparkes]

Thanks for the answers supplying background data, although I'm afraid nothing leaps out at me.

Mentally, I have reviewed several items, and I can't clearly identify what 'might' be happening to cause the effects reported, of heating falling as road speed falls, and heating rising 'too high' initially after a cold start.

Just in case it prompts someone else's train of thought towards a solution, I'll list the items I've reviewed.

These are in no particular order.

In car thermostat.

This tells the HEVAC there is hot coolant available, from which heat can be drawn.

If this falls off the pipe on which it is clipped the HEVAC doesn't blow sufficient air through the heater matrix to warm the interior.

Internal air temperature sensor.

These can become 'insulated' with fluff, which makes the system slow to respond to changes to interior temperature. This insulation might cause the initial overheating after a cold start, but not the sudden temperature drop at roadworks. Rather the interior temperature would rise.

External temperature sensor.

The early version in the heater air intake suffered from picking up heat from an engine after standing. This was shown by abnormally high temperatures being indicated by the External Temperature reading on the HEVAC display. Not a reported problem here.

The later version had the sensor behind the front bumper, if this sensor had fallen off and become more exposed to 'wind chill' the indicated temperature would be unexpectedly low, but we are told the reading was realistic while travelling down the A1. The wind chill effect would drop as the speed falls, and thus the interior heating would fall, as the HEVAC responds, but the exterior reading was not noted as changing. Nor can I see this causing the excessively strong heating performance after the cold start, unless perhaps, the journey immediately went onto high speed roads. But I'd also expect to see unrealisticly low temperatures displayed.

Blend motors.

After an overnight stand these will go to the 'full hot' position on restart, and if faulty this is the most likely time for the cheque book symbol to be indicated. As Ally indicated in an earlier response, during the A1 journey, if the blend motors failed to respond to the drop in natural (cold) air flow as roadworks were negotiated, the interior temperature would rise rather than fall.

Water pump failure (impeller blades breaking, or slipping on the shaft).

Blade breaking is a diesel engine habit, I'm not sure about the petrol. Normally water pump failure results in an overheating engine, which isn't the case reported here.

Low Coolant.

We have already discussed this, and while it fits 'perfectly' the symptoms reported on the A1 trip, it doesn't tie in to the interior overheating after a cold start.

Air conditioning.

This does run during cold weather, as it dries the cooled air, and the dry air helps the Climate Control system perform better (you don't want hot humid air). I can't see poor AC performance giving the reported problems. If the AC fails it is treated as a HEVAC fault, illuminating the cheque book.

That's all I've got for now.

Two faults?

One unoticed during short local trips but becoming apparent during the long trip, then a second or associated fault occuring.

You have had the car for some time, have you identified a local Testbook, Rovacom, Autologic user who can clear the HEVAC fault reports. There will be no indication when these reports were triggered.

Ally will know better than me whether 'silent' reports are generated without the cheque book symbol occuring.

The point here being that you may need one visit to clear the faults, then a test run and second reading to see what new faults have been recorded (if any).

Ally has suggested 'seeing what the HEVAC sensors are seeing'. I think this is referring to a Test Run with the analyzer connected to display the sensor inputs. This data can be captured, my preference is to do this as a CSV file, but it's really down to the operator as to what style he is comfortable with.

I only mention this in case you weren't aware of these facilities of Live Data Display and or Live Data Recording.

Interesting, as I said.

[Ally V8]

A run on Testbook is the answer,as you say David the option of water pump failure would have the engine brewing up in less than 10 mins even in cold weather.Testbook cannot datalog - IDS can,but its perfectly normal when a customer has an issue like this to run Testbook in the car during a drive.The Valeo hevac ecu is not the most reliable,(I've had faulty brand new ones) but live data is really the only way to go with this.How a service manager would want to go about this I have no idea,but most independants ought to be flexible enough to cope.

[Drakes]

SORTED

Took motor into my local specialist who plugged it into the computer and had a fiddle around and found that one of the flaps that the heater motors control was sticking at one extreme of its movement, so they freed it up and adjusted it and all is working okay now. Cost half an hour labour.

P38 heating isn't always expensive to fix just normally!