BlaCkPlaGUE

My buzzer hasn't gone off since I repaired the coolant jackets on the TII housings. I plugged them up and since then I have not leaked any coolant that I can see, I also havent heard the buzzer since. I redid my water pump housing at the same time and after it was put back on, and filled up with coolant, like i said, I havent had to add any since. I am just ideling like I said before, no real stress on the engine or anything.

So your saying that I should turn the heater on full and rev up the engine to see if the buzzer goes off? not sure what your telling me to do there..

thx!!

wangerrr

^ this is most definitely true. Something to do with the density of cold air vs. hot?

BlaCkPlaGUE

No, compression will be BETTER when HOT, NOT COLD. It has nothing to do with air, it has everything to do with the metals.
Metal contracts when cold, this happens in an engine, the parts get smaller, they don't seal as well, they are not to factory spec. Its only when warm that the car will seal properly and build good compression.

Turbonut

iTrader: (1)

Courtesy of Kevin Landers:

A warm engine makes less compression than a cold engine. I have verified this on several engines. This is why we have hot start problems...the rotary loses 5-10psi compression when warmed up. ON some, it won't matter, because compression is still high. But if you have a weak engine already, that 5-10psi drop when warm can be enough to cause startup/flooding problems.

ddub

No you're wrong. Compression NUMBERS will be higher when the engine is completely cold. The numbers from the test will be LOWER on a hot/warmed up engine.

Search, this is common knowledge and has been said many times on here.

BlaCkPlaGUE

WHAT??!! man thats fucked up. I mean, I've been wrong all this time.. Why in the hell do we have block heaters then anyways? It isn't for warming the oil, cause the heater is right beside the spark plugs.

RotaryEvolution

iTrader: (30)

it's better to do a compression test for the area where you are having troubles, not always will a cold engine have more compression than when warm but generally this is true. fact is, if you have cold starting issues but none when warm then it is a good idea to start with a cold engine compression test.

ddub

Compression isn't the only factor in an engine. Just because compression might be 5psi better when cold than hot doesn't mean you don't want the engine to heat up still. You still need the coolant and oil and everything to heat up to operating temp before romping on it.

And it is true that compression can be almost exactly the same when cold and hot, but almost always you will get better numbers with cold compression testing than hot. I've verified this myself with 3 engines all in different quality (one very low compression could blow soon, one 150k mile engine with average compression and ran well, and one rebuild fresh after break-in).

BlaCkPlaGUE

So why do we have block heaters?

ddub

To get everything else up to operating temp quicker. They are used to help get coolant and oil up to higher temperatures faster, it's better for the engine to be running with warmed up oil than cold, sludgy oil. It helps get the metals warmer too. Just because compression numbers are higher when cold than hot doesn't mean it's better. Like you don't want to be spinning to 7k when you car is cold, that'd be bad. So the quicker your car gets to op temp the better. Also, block heaters help reduce pollution as really cold engines have worse emissions than when warm, so the warmer you get the engine faster, the less pollution you will make. This is also why block heaters are standard in lots of vehicles in cold climates.

BlaCkPlaGUE

Well officially i feel like an ***. I've been telling friends and **** the wrong thing for a while now. In fact, I've mentioned it on here for a while too and no one said anything about it.
Not only that, but I was positive thats why mazda made the cold start assist system with the antifreeze! Im positive that I have mentioned that the cold start assist fluid was designed to help build compression during cold starts. I've mentioned it 2 or 3 times and no one has said anything...

iceblue

Think of it this way the reson it is higher cold is b/c metal exsplands when it is heated up. Have you ever had an exhoust leek and like 10 min later driving it goes away. This is b/c the metal has heated up and it exsplands sealing up the crack. Thus if the metal exsplands when warm the housings become larger and separate away from the rotor and apex seals causing lower compreshion. As well warming it up allows evrything to seat up properly.

BlaCkPlaGUE

Yea but the rotors expand too? right? Do they not expand as much as the metal that makes up the housing?

iceblue

They do not exspland as much b/c they are a huge solid pice of metal compared to the housings.

Now if you made the rotor out of aluminum or titanium you would have to build them with as much as a 4mm gape for exspantion. So in this case we would have to rais our compreshion cold to get the motor to turn over

ilike2eatricers

It's ok we all make mistakes.

jhammons01

Coefficient of thermal expansion is the term your looking for. Aluminum has a higher coefficient than does steel. your housings are expanding at a greater rate than your rotors will, due to the metals that are used.

Just to clarify I don't take any side on the compression issue. Just wanted to add my .02 on the metal thingy