Head Gasket is probably fried. No change in EGT's?!

[shealy]

On the weekend, I was heading out to Alouette Lake to do an overnight camping trip with some friends. Near the Pitt River bridge I glanced down at my water temp gauge (stock one) and it was almost completely red-lined. Sh*t!! Pulled over immediately, and let it cool down. I noticed my coolant was bubbling into the reservoir - not good. Luckily, this happened right next to a Canadian Tire, so I ran in, got some coolant, topped her up and "nursed" her back home. Took it in yesterday to CVI, and Butch took a few minutes out of his busy schedule to take a quick look at it (major thanks to him!). Looks like its a head gasket replace. Ugh.....

Anyways, I have a few questions related to this.

1. I put a pyrometer in about a month ago (RichD special!) and have been keeping a close eye on the temps. The probe goes right in where the EGR used to be. To be fair, I've been watching this gauge more than my water temps, but when this "overheat" issue happened, the temps on the pyro weren't abnormal at all. Is this because the probe is right in the cylinder itself? Or is this placement in pyro not nearly as helpful as I thought?

2. My understanding of this is that with the gasket not sealing properly, some of the pressure from the cylinders gets into the coolant in the block, getting air pockets trapped in the coolant, causing it to not circulate properly through the radiator etc. Would this perhaps explain the difference in EGT vs. water temp readings? And is this maybe a good reason to install a more accurate water temp gauge?

Thanks guys - just trying to wrap my head around what exactly was/is happening here!

-Steve

[Mr. Flibble]

The pyro is part of the turbo, and it monitors the exhaust gas temperature (EGT). The temp of your exhaust is not really related to the temp of your coolant, it is to some degree, but not all that much.

In your L300, the turbo is cooled by oil, and any extra heat from the turbo either goes out the tailpipe, or gets removed by the oil. This oil then goes into the engine, dumps its heat in the engine and that gets removed by the coolant. This part of the engine with the coolant is where your head gasket comes in. So, extra heat in the turbo eventually ends up in your engine over time - but not always.

The real reason for a pyro is to prevent your turbo from overheating, not your engine so much. It is true that if your pyro is reading hotter, this will almost always mean that your engine will be hotter, but the reverse may not be true, as it was in your case.

However, your head gasket going leaks coolant into you cylinders or oil into your coolant, maybe both. You can have your engine seize from too much coolant in the cyls, or have the lubrication destroyed by the mix of oil and coolant in your engine, looks all like a timmy ho's double double in there when that happens... Happened to my Toyota 4Runner and totally destroyed my 22RE engine when my head gasket went.

Still, while the head gasket is failing, you lose coolant somewhere, cyls, engine, out to environment... so you are losing coolant. That means that your engine can't dump the heat that it has, and it starts to overheat. To make things worse, depending on where your water temp gauge is, you could lose some coolant, and it would leave air where your temp sensor is (this happened to me) so your engine reads as cool, when in reality it is overheating because the coolant never reaches high enough in the engine to get to the temperature sensor!

[shealy]

My pyro probe is attached to my blanking plate where my EGR was removed, not in the manifold post-turbo. I was under the assumption that this went straight into one of the cylinders in the engine (cylinder #3 I think?). Am I totally wrong in thinking this??

[Mr. Flibble]

My pyro probe is attached to my blanking plate where my EGR was removed, not in the manifold post-turbo. I was under the assumption that this went straight into one of the cylinders in the engine (cylinder #3 I think?). Am I totally wrong in thinking this??

Yes, it is going straight into where the exhaust is coming out of the cylinders in the engine, but not into one of the cylinders themselves. The glow plugs do this, but your EGT probe does not. If it went into one of the cylinders itself, it would only give you the temperature of that specific cylinder, and not the remaining three, or the proper temperature of the exhaust gases about to go into your turbo. Where you have it mounted is really good, as this gives you the temperature of the gas going INTO your turbo, as opposed to what is coming out. This means that the estimate of the temp of your turbo is more conservative, and you are much less likely to damage your turbo, and be more likely to react in an appropriate manner when you see the temp rise, it probably gives you a few more seconds of grace to ease off the gas pedal.

In an ideal world, you would have a probe both before and after your turbo, showing the difference. This would also give you an idea of how much the turbo itself is soaking up.

[Luna-Sea]

Hey,
Hopefully you did not crack the head my friend!
Your EGR EGT guage WILL most certainly help you preserve a head as well as your Turbo.
The head gasket failure was just not directly related to
Your EGT at that instance.
Those auber type guages are great, I thought (ask RichD)
You can set alarms on them to.You can use different sensors on them too.Always thought that
Would be a kickass idea for a water temp guage in
Our delicas as one can be distracted by good weather,
Tunes ect. And not always giving the water temp guage
A look every half minute.
That would really be helpful and preventative piece of gear.

Good Luck!

[shealy]

I guess the moral of the story here is that pyro gauges aren't the be-all-end-all of gauges for our rigs. Make sure your water temp gauge is working and keep a close eye on it as well. Luckily I was still watching it from time to time and noticed before I did even worse damage to my engine!

[shealy]

Talked to Butch earlier today. Confirmed: head gasket needs replacing.