Thread: Modifying Thermostats

This is the same/similar issue I'm having(with A/C).
No matter how hard I try, no A/C coolant temps run perfectly fine.
AC and any load sees coolant temps run far too hot(for my liking).

I'm Ok on the flat and slight inclines with the 90°C running with AC on. No issue with 90 or 95°C at all.
It's the 115-117°C that worries me with AC on, and up a long hill, at any speed, gear or backing off.

For now, my solution is to remove the grille(D1) which then has the tdi running fine, no matter how hard to try to get it to run hot.

Strangest of strange things is too:
I cracked the fan shroud one day a long time back, and having removed to to epoxy it(now well and truly hardened up) .. I find that I get few degrees cooler without it.
So I haven't had it back on since Summer '16 now.

Peeked inside rad, and not obviously blocked up(though haven't pulled it apart to confirm small blockages).
Feeling inside via the rad hose ports, no gunge, buildup or oilyness .. feels basically clean and dry(dry as in not gungy/oily) in the side tanks.
But there could still be the chance that it needs rodding to be sure it's 100% perfect.

I'd recommend to listen to the comments re not modding the thermostat.
Maybe change it to a better/newer one.
From my recent experience, I reckon the waxstat branded (or marked) ones don't seem to be as good as the Tridon versions I got.
The tridon opens better(better flow).
Although, it could be that the waxtstat was just older and less responsive.

What car(ie. D1 or Defer), and what gauge setup do you have?
I find the strongest correlation to coolant temp for a good running vehicle is that EGT determines coolant temp for the most part.
That is, you can have hot coolant temps, but not have hotter exhaust temps, but if coolant temps are slightly warmer than a baseline, then high EGT will see coolant temps skyrocket!

eg. my normal coolant temps is about 80, maybe 83°C. no AC, doesn't matter how hot it is outside. If EGT rises into the high 600's, I then get 85-88°C coolant temps. That is, give it a long hill, where EGT will increase(ie. load) and coolant temps will reach 88°
Never seen more than 88 with AC on.
I'm perfectly happy with that.
It's about 88 where I can hear the VC lock up and come on.
With AC on, I know that the condenser/thermo fans are both on, could be as low as 25°C out, and EGT rises a bit faster up this same hill, so I have to back off earlier, coolant will peak at about 105°, where a few minutes earlier it peaked at 90 for a sec or two and dropped back to 88.

I've seen 117° up this same hill, same time same load.
I use the 700°C recommendation as my peak EGT for a few minutes only.

Going back to do it again, this time with grille off, EGT in the high 600's, coolant peaked at 95 with AC on, basically the same with AC off(at 88).
So for me now, I use my grille as a simple fix in hot ambient with AC on. BTW don't usually use AC tho.

The common theory is that high EGTs is a result from tuning the injector pump, but I reckon that's not entirely true.
I get high EGTs now simply by adding a more restrictive rear muffler(less drone) to mine .. which I have to undo one day again, and put up with the drone a bit more.
Also, loss of turbo pressure should cause higher EGT. Maybe no critical, as in 700's but higher than otherwise.
I have no idea what a bog standard tdi will register in terms of EGT .. never had a bog standard Tdi to play with!
But a loss of boost is similar to richer fuelling .. same amount of fuel with less air.

Check air cleaner, do you have a snorkel, are your exhaust/muffler(s) not blocked, has the rad been confirmed clear, unblocked, etc. etc.

have you done the simple trick of blowing through the radiators(both from behind and the front) with a garden hose.
Amazing how much muck/insect debris gets built up over the years. NEVER use a high pressure washer through the radiators, unless you want to replace them.

Originally Posted by DiscoMick

Is your radiator OK or stuffed?

Moi?

Feels fine, but not 100% confirmed.
By the sounds of it, you'd think mine was stuffed, see that the removal of the grille helped temps so much.
But then if it were, when worked hard even with AC off, you'd think that a dodgy rad would still give high coolant readings, but it doesn't.

I do have an aluminium rad to try out, and a double thickness core IC to boot.
But I want to install them together in an aluminium frame, rather than mod my std radiator frame to house the thicker IC.

The other reason I reckon my rad is OK, is that over the winter months, and up to about 18-ish °C I can easily run without the engine fan installed, and still don't get more than 83°C operating temps.
Doing this lets the engine warm up quicker, by at least 5 mins quicker.
Up to about 20°C ambients, running with no fan, max coolant temps I've seen are in the low 90's but cool down quickly even at walking pace when in traffic.
Driving included being stuck for 20 mins behind a string of cars all stuck behind a tram, or running on a freeway in traffic. Makes no difference.
I'm pretty sure if I had radiator issues, then two back to back 20 min drives in traffic would reveal it with the engine fan removed!

Scared crap out of myself tho with no fan one day.
Up the hills to Ballarat, I saw high 90's in low ambient temps... can't remember exactly, but had to wear really warm clothing that day .. maybe low teens.

So on the highway with engine under load, I can confirm that the fan does do a fair bit of work.