Thermostat/Temp Gauge Question

[joebillhill]

My temp gauge was reading pretty low as of late so I decided to change out the thermostat along with flushing the system and putting new fluid in. I drained the radiator and engine, filled the system with water, ran it 10 mins or so with the heat on and off, and topped off a little bit until the engine heated up a little bit and water started coming out the top of the radiator. The old fluid came out orange-ish green with no flakes or gunk. I repeated this three times to get the fluid pretty clear and put the new thermostat in.

It seemed weird to me that at no point did I notice a definite drop in the radiator fluid associated with the thermostat opening just some occasional bubbling.
Also, I wasn't able to put in the whole 9 liters, only about 5-6. This doesn't surprise me too much since the second drain still had a lot of green color to it meaning that the whole system didn't drain.

A couple questions came out of this

1: If the engine gets drained and the engine gets started up (thermostat closed) will there just be air around the engine that will heat up, not be able to absorb/transfer heat as well and cause damage to the engine before the thermostat opens?
2: If that void was getting super heated would the temperature gauge recognize it? Or does it need fluid passing by it?
3: How does having the heat on open up the thermostat?
4: Can the whole system be drained through the radiator drain and engine block?

If anyone notices anything weird about this situation too, let me know. Part of me wants to drive around to knock loose air bubbles and heat up the engine to try to really open up the thermostat but part of me is worried if I've somehow got a big engine melting air bubble.

Thanks,
Joe

[motorang]

Hi,
the thermostat does not completely block the coolant flow, just partially restricts it. So no need to fear an airlock there. You do not notice an opening thermostat by a change in water level or bubbles or anything. Seems all pretty normal to me.

The thermostat is only actuated by the temperature of the engine coolant. The heater is put to max to have maximum coolant flow there. Do you have a rear cabin heater as well? Was that in "hot" position as well? I think the hoses of this one sit lower than the rad so may need an extra drain.

Andy

[Growlerbearnz]

"...filled the system with water..." Just checking, but you mean "water and antifreeze mixed to the correct ratio", right?

Our engines need antifreeze/corrosion inhibitor to stop the alloy head and cast iron block from corroding each other and creating sludge.

Anyway- your questions:

1) as Motorang says, the thermostat doesn't trap air in our engines. Apart from having a small bypass built into it, it's quite low down on the engine- the engine block fills from the top hose as well as through the lower hose/thermostat. The only part that traps air is the rear heater, and that can be a pain to bleed. Luckily it tends to stay full when you bleed the rest of the system.

2) If there *was* a void that became superheated, the temperature gauge would not see it. The temperature gauge only shows the temperature of the coolant passing the sensor just before the top hose. Steam is hot, but not very conductive so if a steam bubble were to pass your temperature sender you'd probably see the temperature go *down*.

3) The heater bypasses the thermostat. Turning the heater on allows any air bubbles to go through the heater, past the thermostat, whether the thermostat is open or closed. It also means you get hot air as soon as possible, not just when the engine's up to temperature and the thermostat opens.

4) the radiator drain gets 90% of the coolant out. The engine block drain (if fitted) doesn't seem to do much- maybe another litre or so? The front heater can be drained by disconnecting the hoses where they attach under the floor- above the air intake splash guard. As I mentioned before, try and avoid draining the rear heater.

[joebillhill]

Thanks for the clarification guys!
Yes, water/coolant mix Growlerbearnz, It's getting warm here but not that warm. Also good to know about the corrosion inhibitor (I was wondering about coolant ratios in tropical zones the other day )

[Growlerbearnz]

Cool. I just follow the mixing ratios on the pack of antifreeze- some newfangled antifreeze is already pre-mixed! What will they think of next, pre-sliced bread?!

[joebillhill]

Loaves that are cut 50/50? Amazing
So now that I have all that sorted out I'm curious what else would be causing my system to heat so slowly. The thermostat is new but it takes a really long time to get up to temperature on the gauge (a warm up of a few minutes and then a few miles down the city streets)
Temperature sensor?
Would anything else mechanical cause it to be slow?

[Growlerbearnz]

I've been watching my temperature gauge lately. From cold at idle it takes about 10 minutes until the needle is just in the normal range (at the lower mark). If I just drive from cold, it takes about 4 minutes/3km before it's at the same point.

From there, it takes another 5 minutes or so to get to normal-normal, about a third of the way up.

If you're not making any boost though it's going to run pretty cold.

[joebillhill]

Good to know. Thanks, Growlerbearnz. How would lack of boost affect the temp? Just lack of oxygen leading to less fuel burning, causing lower EGTs? Or something else?

[Growlerbearnz]

TL:DR; You're correct, lack of air makes for less efficient combustion, so less heat in the coolant.

Longer, more comprehensive answer:

On a correctly tuned engine, all the combustion happens inside the cylinder and is finished long before the exhaust valve opens. Most heat loss is into the cylinder head and block and so into the coolant. Higher boost makes the combustion hotter and faster which raises coolant temperatures in proportion to EGTs.

Some situations lead to combustion happening slower. Things like low cylinder pressures (idling, engine wear), cold cylinders (temperature, glow plugs not working), overly rich mixture (like if your IP doesn't know your turbo's not making any boost) can mean that the fuel is still burning as it goes out the exhaust. This generally exposes the coolant to less heat, while raising your EGTs.

Pretty much anything that causes black smoke is an indication that your combustion isn't happening efficiently, and you're probably putting extra heat into things that aren't designed to take it.

[ChuckBlack]

As to your cooling system flush, i recommend redoing it as so, disconnect the lowed rad hose and upper one. connect a air line/water pressure to the opposite cooling circuit and blow air and pressure water in the system(Engine back flush). Do this until plain clear water comes out the other side. Remember to collect any waste, particles and contaminated water!!! Remember to do this on the engine side only. Once finished, remove all drain plugs from engine side walls and reinstall with proper thread sealant. Choose a non mixed coolant such as Extended Life Coolant which are designed exclusively for smaller diesel engines and reinstall all hoses... I posted a thread on upgrading the cooling system and i saw a definite change in performance!

[joebillhill]

Hey Chuck I looked for your post but didn't see it. Mind posting the link?
Thanks,
Joe