MGTF Blinking Warning Light and Slight Mayo on Oil Cap - Is this dreaded HGF?

Hi peeps. This is my first thread on the forum and I wish it was one to show my car, however it's developing some issues and I need your help!

My MG TF 160 (with about 82k miles) has been pretty great for the 10 months I've owned it. It passed MOT a few months ago no issue.

This has all changed since about a week ago, when I was driving for roughly an hour on the motorway in hot weather, and after leaving the motorway and going about 40mph the engine warning light began to flash, but within about 30 seconds went out.

I pulled over in a panic and rang my local MG specialist, they advised me to bring it in for a check so I drove straight back them, nursing it all the way. He couldn't really tell me what the issue was exactly, it appears to be a misfire according to codes. I had the sparks changed only 3 months ago. On his suggestion I drove some more spirited drives to try and get the light to reappear so they can 'book me in'. I've since done 2 spirited drives and again nothing, drives fine and sounds good, temps etc.

Today, I decided to check the oil filler cap and noticed just a small amount of mayo on the edge, nothing like you see on some pics where it's like a Guinness, it was easy to wipe off. I checked the dipstick and there doesn't seem to be any signs of mayo.

My main worry as you can imagine is that I have the dreaded HGF and water is mixing with the oil.

Am I over worrying, or am I correct to?
by Rajie

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Sorry to hear this but it is probably nothing to worry about.

I assume the garage checked the ECU fpr fault codes and then cleared them.

What state is the coolant?


Home to black Alfa Romeo 159 3.2 V6 Q4 ,green MGF VVC and red MG Maestro T16.

MG - the friendly marque.

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Sorry to hear this but it is probably nothing to worry about.
Thank you and glad to hear it might be nothing to worry about, gives me hope!

I assume the garage checked the ECU fpr fault codes and then cleared them.
That's exactly what happened. I drove after almost hoping for a light so I could send it straight back, but nothing so far. The mechanic seemed pretty chill about it.

What state is the coolant?
Overall it seems ok but I did top up today as it lost some coolant. It's seemed to hold on pretty well so far. I've read that coolant needs to be monitored and possibly topped up occasionally, which makes it seem hard to diagnose what or where the issue is. I'll open the cap tomorrow to see if there's any 'gunk' in the tank.

Scouring the web and reading what there is on this, HGF seems like a real life nightmare! Haunts you even if it isn't real :lol:
Last Edit:3 weeks 6 days ago by Rajie
Last edit: 3 weeks 6 days ago by Rajie.

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  • Cobber
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HGF is a bit of a boogyman for these cars, to much has been made of it and as such everyone is overly paranoid about it.
Yes it is a real problem, but no more so than on many other cars.
So lets look at the various reasons why head gaskets can fail on our cars.

The early MGFs came out with plastic head locating dowels, a bloody stupid idea which didn't do much of a job of keeping the head located. And if fitted most likely have been replaced with steel ones by now.
The cylinder head can fret (move about a tiny bit) thereby fatiguing the gasket.
There are other causes of cylinder heat fretting that have effected our engines, early heat gaskets were of a different design and inferior to later designs.
and the fact that the head studs go straight though the engine block to also secure the crankshaft main bearings as well, can cause problems.
Such long studs can stretch a bit more that shorter studs, and it is critical that they are replaced and tensioned properly when the head is removed. There are up rated (better quality) head studs available.
Some later engines had a more ridgid stud girdle, often refereed to as an oil rail on our engines as it also distributes the oil to the bottom end. This also uses the go through head studs and increases the rigidity of the engine.

These engines have separate cylinder liners sometimes the cylinder liners aren't sitting properly which makes the surface that the head gasket seals uneven.
This problem is most likely to occur when an engine has had it cylinder head removed for repair, the cause is sloppy workmanship, by the mechanic that did the work.

Over heating due to a variety of reasons such as loss of coolant and various failures like: waterpump, fan, drive belts, hoses, radiator etc. Another problem that is common to all cars but our cars in particular is the coolant filler cap, it has a pressure relief valve integrated into it, this isn't always the best quality, and it can leak away you coolant. In fact I recommend caring a spare in the boot or glove box at all times.
Proper preventative maintenance is key here. That and and the fitment of a "Low Coolant Warning Alarm" is essential for ALL cars, IMHO, but it is perhaps more so with our cars.

Heat stress over time, can shorten the life of heat gaskets. many heating and cooling cycles can cause stress to a lot of engine components and the limited airflow of a mid engine layout inherently contributes to this. This can be minimised by keeping the cooling system in top condition.

There are other more exotic and unlikely reasons for head gasket failure, which I won't bother to mention now, otherwise this post will read like bloody War and
Peace!

So what are to most important lessons here?
* A low coolant alarm is essential for our cars and if not already fitted one should be fitted ASAP!

* Proper maintenance is of the utmost importance and should be done by a competent person.......no elcheapo shortcuts and quick fixes!

* Where possible uprated components should probably be used whenever major engine surgery is done.

Now we can go to properly diagnosing a buggered heat gasket.
A little snot on the oil cap can be due to condensation, but if noticed a proper diagnosis must be done.
A proper diagnosis should be done if an unexplained loss of coolant is noticed a or if there is any other reason to suspect HGF, such as over heating. such as globs of oil in the coolant.


* Check to oil, pull the dipstick and look at the quality of the oil is it nice and clean, darkly blackish, dirty black sludge or greyish white snot the latter 2 should be attended to immediately the black sludge indicates poor maintenance and needs changing ASAP but doesn't necessarily have any implications of HGF, however if the dipstick shows greyish white snot then a buggered heat gasket is highly likely. There are other potential caused for water getting in to the oil but HGF is the most likely.

* Remove and inspect the spark plugs, water droplets on the plugs is a dead give away, as is great gushes of water coming out of the plug hole whilst the engine is cranked over by the starter! An unusually clean spark plug is also cause for suspicion, any coolant getting into th combustion chamber can effectively steam clean the spark plug. whist you have the sparkplugs out you can go to either of the next two diagnostic checks.

* A compression test should be done this will indicate poor compression which can be caused by HGF, cracked cylinder liners, cracked cylinder head, poor valve sealing, or bugged rings and or bores. the Gauge is fitted to the sparkplug hole and the engine wound over on the starter to see how much compression is available.
you are looking for consistent readings across all the cylinders within @ 10% of one another, the exact pressure reading doesn't matter much. other tan to say there must be at least 80 psi.
Any discrepancies in the readings can indicate HGF, if only one cylinder is low then all of the options above may apply. If two adjacent cylinders have the same or very close low readings then the most likely cause is siamesed cylinders, this happens when the head gasket fails between the two cylinders, but can also indicate a cracked cylinder head. Either way the head has to come off!

* There is a similar test to the compression test, this is a cylinder leakdown test, like a compression test a pressure gauge is fitted to the sparkplug hole, but this test involves you you aligning the cylinder under test to top dead centre with both intake and exhaust valves closed. Then compressed air is applied the cylinder' a pressure reading is then noted. Once the pressure has been supplied the supply is turned off and the gauge observed any quick loss of pressure can indicate problems, if you ca hear air leaking from the exhaust then a damaged exhaust valve is the most likely problem, the sound of air leaking from the intake, will tell you the inlet valve is the most likely culprit, Is air is leaking it to the cooling system? then bubbling may be seen under the coolant filler cap. and if air can be heard leaking into the crankcase then that's also bad. the later two could be HGF or other problems needing more investigation.
The advantage of the compression test is it's relatively quick and easy in comparison with the cylinder leakdown test, which has to be done one cylinder at a time.
Different equipment is required for these tests.

* A coolant system pressure test involves fitting a test unit to the coolant filler cap, this unit has a gauge and a pump, you pump the pressure up to around 15psi and note how long it takes for the pressure to drop, a quick loss of pressure can indicate HGF, but it can also point to other problems, such a leaky radiator, welch plugs, cracked block, buggered water pump bearing, bad hoses or connections to name a few. While the system is under pressure you can do a thorougher inspection around all the various components that carry coolant around the car for leaks. The same equipment can be used to test the pressure relief valve in the coolant filler cap if the kit comes with the appropriate adapters.

* A coolant sniff test, is another way to check for HGF, a cracked head or cracked liners. The process involves a simple tool that is fitted in place of the coolant filler cap that consists of a clear chamber that contains a blue fluid that turns yellow if there are combustion gasses present in the coolant, indicating a problem.
Like the coolant pressure test this test can't test for all types of HGF only those that concern the cooling system they may but won't always indicate if the HGF is only either siamesed cylinders, combustion gasses or coolant are leaking in to the crankcase and other less common types of HGF like oil, combustion gasses or coolant leaking to the out side of the engine, though a coolant pressure test might show the latter if it's bad, but the more common weep may not show.

Another potential cause of overheating and therefore HGF is a knackered thermostat, these can either get stuck open allowing over cooling of the engine, or worse stuck shut thereby overheating it!
Removal of the thermostat is required to do a visual check, a thermostat that is stuck open should be obvious and should be replaced, you should never run an engine with it removed as the coolant may not circulate around the engine in the ways it was designed to causing localised hot spots.
A thermostat stuck or sticking closed will obviously cause over heating, this can be tested by placing the thermostat in a suitable container such as a small saucepan and heating it on a stove with a with thermometer to monitor the temperature that is required to open the thermostat.

Now there are probably a few points that I've missed, and I've had enough of composing this great volume for now and if you've read this far I assume that you've had enough of reading it!
I have no doubt there will be others that will come along and add to this, and they're bloody well welcome to do so.

"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"

by Cobber
The following user(s) said Thank You: David Aiketgate, EllisoJo, MAXTHEDOG, Notanumber, Rajie

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You have a couple of professorial replies and I cannot do better.

My recent "mild" HGF included the symptom of more of the steamy stuff coming out of the exhaust. We all get a bit when the exhaust system is heating up but this was noticeable when looking in the wing mirrors. It would need a drive in the early morning when the air temperature is low, at this time of the year. Yes, I had mayo on my stick and low coolant warning.

I feel that the engine management light is a red herring or at least, not the symptom to be led by if it is HGF.

As a general question to those who know, how much coolant loss is "normal"?
Last Edit:3 weeks 6 days ago by generous_dad
Last edit: 3 weeks 6 days ago by generous_dad.
The following user(s) said Thank You: Rajie

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With regards the miss-fire codes , get your 'Man' to check the plug leads where they enter the coil packs . I had exactly the same issue with my TF (135) and the Verdigris on the copper end of the leads was the cause. I cleaned mine up and the miss vanished , the code has also never returned . :yesnod:

John .
The following user(s) said Thank You: Rajie

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HGF is a bit of a boogyman for these cars, to much has been made of it and as such everyone is overly paranoid about it.
Yes it is a real problem, but no more so than on many other cars.
So lets look at the various reasons why head gaskets can fail on our cars....
This is amazing! I'm literally re-reading and trying to commit to memory all these key things for when I chat to the specialist.

I've been re-checking the oil cap since I cleaned it up and no mayo's appeared, although I don't know normally how long it takes to build. Same with the coolant level. So far so good, but will see after a long drive this Friday, fingers crossed. Again thank you for this detailed post.

With regards the miss-fire codes , get your 'Man' to check the plug leads where they enter the coil packs . I had exactly the same issue with my TF (135) and the Verdigris on the copper end of the leads was the cause. I cleaned mine up and the miss vanished , the code has also never returned . :yesnod:
Cheers, I will mention this.
Last Edit:3 weeks 2 days ago by Rajie
Last edit: 3 weeks 2 days ago by Rajie.

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+1 for checking the state of the plug leads and coil packs. Their connections can get dirty and also sometime the insulation on the caps can disintegrate causing inevitable misfres and poor running. To control costs, good 2nd hand coil packs and leads can usually be sourced

2003 TF 135 sunstorm

Last Edit:3 weeks 2 days ago by Notanumber
Last edit: 3 weeks 2 days ago by Notanumber.
The following user(s) said Thank You: Rajie

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Earlier VVC cars had a coil pack “block” bolted to the rear of the engine & loooong plug leads to the head, I’ve changed this now to the later & now more conventional plug cap coil.
This was prompted by an occasional miss fire & I included a picture which tells the remainder of the story.
Last Edit:3 weeks 2 days ago by Airportable
Last edit: 3 weeks 2 days ago by Airportable.

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