Problems after a head gasket replacement

This is the Forum for all your Peugeot Technical Questions, Problems or Advice.

Moderator: RichardW

SMA207
Posts: 9
Joined: 24 Jun 2021, 00:12

Problems after a head gasket replacement

Post by SMA207 »

Hi
Im looking for some guidance with a problem with my daughter 2008 207 1.4 8V manual. Having driven it with a coolant leak the head gasket failed and I have replaced it and had the head skimmed. New bolts were used and the thermostat housing on the side of the cylinder head was replaced which was the location of the leak. I have followed the Haynes manual carefully and the car started first time. However the Haynes manual makes no mention of the procedure to put the ECU into coolant bleed mode. I just filled it up at idle until no bubbles came out of the bleed points as per haynes.

Its covered about 1000 miles since and ive noticed that the temp gauge is not rising as expected to normal even on the hottest of days in traffic for extended periods. If I fast idle the engine while stationary I can get the temp gauge to rise to mid scale and eventually the fan kicks in, or if i drive it hard up steep hill i can make the gauge rise off 70 deg. It was MOTed after the head was fitted and the tester said it ran cool during the emissions test and the emission were OK.

I checked under the bonnet after a 35 min drive yesterday and saw that the top hose was very hot to the touch and rock hard with pressure so much so there was coolant being forced out of the temp sensor threads. The cabin heater was only able to produce warm not HOT air. having read the threads I now know the thermostat is controlled by the ECU but I think it might be sticking The coolant level appears constant at MAX on the expansion bottle.

Please can you guide me to what to do next, I was going to replace the thermostat

Thanks in advance

User avatar
white exec
Moderating Team
Posts: 7019
Joined: 21 Dec 2015, 13:46
x 1325

Re: Problems after a head gasket replacement

Post by white exec »

Hi, and welcome!

That does sound like either a thermostat malfunction, or a stubborn airlock near the gauge temp sensor. The temp gauge behaviour sounds erratic, but complaints about temp gauges reading low a lot of the time are not unusual.

Long-shot, but I wonder whether the new (revised?) thermostat+housing and your presumably original gauge sensor are properly matched? Marc might know if there were any changes to the spec of either, and whether/not they should be replaced as a pair.

The solid top hose doesn't sound abnormal, but the pressure should not be causing a leak anywhere, least of all the sensor, unless it was poorly fitted.

There may be a specified bleeding procedure for the engine (again, someone here will know), but - in general - after work on the system (or coolant change/draining) the engine should be brought up to full working temp while idling, and bleed screws repeatedly opened until the cooling fans have cut in at least twice. Revs increased to 2000 or so for around 20secs will help chase out trapped air, as will squeezing the top hose hard to 'burp' the system. Using a 'header bottle' may or may not be applicable to bleeding your system.

The lukewarm cabin heater says that everything is not ok. The heater matrix should be at the same temp as the engine block at all times, the minimum running temp guaranteed by a working thermostat. Lukewarm heater suggests either airlock, blockage, or thermostat being leaky (ie not fully closed when emgine is cold/cool).

When you start the engine from cold, heat build-up should be detectable in head and the heater feed pipes long before any heat is felt in the top hose. If all warm up at much the same rate, that suggests a 'stat not able to remain fully closed.

SMA207
Posts: 9
Joined: 24 Jun 2021, 00:12

Re: Problems after a head gasket replacement

Post by SMA207 »

Thanks chris the temp sensor is new Im going to refit the old one and try that. The thermo housing was from ebay £18 not £170 oem.
I don't think it is an airlock based on squeezing the top hose and the air that did come out I think it in a blockage or faulty thermostat but learning that it was ECU controlled throw me.
I look forward to the thoughts of others and ill try them all. Its only done 63K had a new clutch timing belt water pump and so on so I dont want to give up on it becuase it drives great!

User avatar
white exec
Moderating Team
Posts: 7019
Joined: 21 Dec 2015, 13:46
x 1325

Re: Problems after a head gasket replacement

Post by white exec »

Marc, here, knows the ECU controlled thermostats well, and will probably be able to advise on how to check/test it.
I think it can be disconnected or powered up, to prove a point - but be advised by the folk who know the detail.

Do check out how the heat migrates after starting from cold, though.

SMA207
Posts: 9
Joined: 24 Jun 2021, 00:12

Re: Problems after a head gasket replacement

Post by SMA207 »

Update
Using the infor from this forum, this morning i started the engine from fully cold. i let it idle for 20 seconds then fast idle for 20 seconds at 2000 rpm then idle for 20 seconds. The top hose was not pressurised and saided cold. squeezing it effected the coolant in the tank.
After a about 60 seconds the feed and return to the heater matrix were fully hot. with the tank cap off no bibbles were seen in the tank and the bleed valve on the heater feed produced no air only coolant. the top hose was cold. Im thinking a stuck thermostat?
what do you guys think?

User avatar
GiveMeABreak
Forum Admin Team
Posts: 24442
Joined: 15 Sep 2015, 19:38
x 2671

Re: Problems after a head gasket replacement

Post by GiveMeABreak »

PSA use a filling cylinder and rod to assembly that goes on over the expansion tank for degassing.

You must ensure the A/C is OFF before doing this.

The long rod is used to open and close the tank safely during the process, but essentially for non-Euro 6 vehicles which yours will be,
Open the rod on the filling cylinder
Start the engine
keep the engine speed at 1500 - 2000 rpm, up to the second cooling cycle (cooling fan(s) cutting in and out).

Stop the engine
Leave the engine to cool.
Blank the filling cylinder using the blocking rod.
Remove the filling cylinder, plug and adapter assembly.
Check the coolant level when cold.
Top up the coolant to the "max" level (Cold).

The full procedure is similar as most PSA vehicles and full details are in the resources section here:

viewtopic.php?t=64036

Access to this section does require a Forum donation off £10 though - but this will also allow you to request official part numbers and parts diagrams for up to 2 years.

User avatar
white exec
Moderating Team
Posts: 7019
Joined: 21 Dec 2015, 13:46
x 1325

Re: Problems after a head gasket replacement

Post by white exec »

SMA207 wrote:
25 Jun 2021, 20:25
Update
Using the infor from this forum, this morning i started the engine from fully cold. i let it idle for 20 seconds then fast idle for 20 seconds at 2000 rpm then idle for 20 seconds. The top hose was not pressurised and saided cold. squeezing it effected the coolant in the tank.
After a about 60 seconds the feed and return to the heater matrix were fully hot. with the tank cap off no bibbles were seen in the tank and the bleed valve on the heater feed produced no air only coolant. the top hose was cold. Im thinking a stuck thermostat?
what do you guys think?
What you describe there – hot heater feed and return hoses, but still cold radiator top hose - is EITHER a stuck-closed thermostat (which would go on to produce cause serious overheating), OR a normal state of affairs IF the opening temperature of the thermostat had not yet been reached.

Some 'stats open only at 85-88°C, which is pretty damn hot (domestic hot water is usually around 65°C). They are designed to keep the engine block (and cabin heater) at/near 90°C, which is the most efficient operating temp for a petrol/diesel engine. In very cold winter weather, the thermostat may only be a crack open, even when driving at speed.

A build-up of pressure in the system is a good sign (it prevents boiling), as is 'no bubbles' in the header tank.

The bleeding technique which Marc describes is simply designed to add a temporary higher header tank to the existing one, to help force air out of the bleed screws. A home-make one might look like this:
.
Coolant top-up bottle 3.jpg
Keep the bottle at least half full of coolant, while bringing the engine up to full working temperature (signalled by the cooling fans cutting in a couple of times).
While you do it, repeatedly squeeze the large top hose to 'burp' air out (you'll see any dispelled air bubble up into the temporary bottle), and open the bleed screws a few times each, until no more air comes out of them.
Leave the bottle in place while the engine cools, then remove it, and return the coolant level to the correct one.

User avatar
GiveMeABreak
Forum Admin Team
Posts: 24442
Joined: 15 Sep 2015, 19:38
x 2671

Re: Problems after a head gasket replacement

Post by GiveMeABreak »

Yet another use for a Fairy Liquid bottle....

SMA207
Posts: 9
Joined: 24 Jun 2021, 00:12

Re: Problems after a head gasket replacement

Post by SMA207 »

Thanks for the extra info i will try it and ley you know what happenes

SMA207
Posts: 9
Joined: 24 Jun 2021, 00:12

Re: Problems after a head gasket replacement

Post by SMA207 »

Update 2
I plugged my cheap ebay OBD2 reader into the car when the engine was cold. it should the coolant to be at 8c the air temp was 16c I thought this was odd Having idled the engine for a minute or two the reading was 26c. The heater feed and return were warm and the top hose was cold. so i swapped the temp sensor that came with the new thermostat housing with the old one and the reading changed to 65c and the gauge went up. After 2 more minutes of idle the gauge showed just under 90 and the IBD2 87c the top hose was hot. Ive taken it for a run i could see the system trying to maintain 89c from the OBD2 live data function. I used fast idle to getit up to temp the fan came on at 105c on the OBD2. When i set off again the temp quickly returned to 89c
I think this has diagnosed a faulty or incorrect engine coolant temp sensor which was failing to control the thermostat.

User avatar
white exec
Moderating Team
Posts: 7019
Joined: 21 Dec 2015, 13:46
x 1325

Re: Problems after a head gasket replacement

Post by white exec »

That all makes good sense, so well done for chasing that through. =D>
I have a vague recollection that some of these 'intelligent' thermostats were re-designed after a problem, so wonder whether they might no longer match up with the temp sensor.

What you now describe sounds like perfectly normal running.

SMA207
Posts: 9
Joined: 24 Jun 2021, 00:12

Re: Problems after a head gasket replacement

Post by SMA207 »

Thanks everybody Ill see what happens! and let you know

SMA207
Posts: 9
Joined: 24 Jun 2021, 00:12

Re: Problems after a head gasket replacement

Post by SMA207 »

UNEXPECTED AND UNWELCOME DEVELOPMENT
While checkinh the coolant level i noticed a small leak from where the thermostat housing meets the head. I had used some blue gasket sealer when i rebuilt it but i think i must have over tightned it and squeed all the sealer out at one tiny point.
What sealer to you recommend for this joint?

User avatar
white exec
Moderating Team
Posts: 7019
Joined: 21 Dec 2015, 13:46
x 1325

Re: Problems after a head gasket replacement

Post by white exec »

Hylomar Blue is extremely good for this sort of thing.
Thoroughly clean the surfaces (with solvent, if needed), and apply evenly and thinly (brush) to both surfaces, and allow to go tacky for a few minutes. Then assemble.
The stuff works similarly to a Post-It note.
Fuel, oil and coolant proof, it has a high industry rating.

SMA207
Posts: 9
Joined: 24 Jun 2021, 00:12

Re: Problems after a head gasket replacement

Post by SMA207 »

I'll get some. How tight do the bolts need to be I suspect I over did them and squeezed the sealant out!