Coolant drain plug on back of engine block. Metric? Size?

I found a coolant drain plug on the back of my engine block.

I need to find out if it's metric or imperial and the thread count. I'm going to install a circulation tank heater instead of a regular block heater and i will need to get the right nipple for it.

It's below the exhaust manifold at the base of the cylinder wall. I can post a pic if needed.

I don't want to remove it just to measure it for obvious reasons.


Thanks.

 

I'm going to start a thread soon. I need to find the right fitting first.

The t-stat does not come into play. Return will be one of the heater core lines on the side of the head. The heater lines circulate through the head independent of the t-stat. That's why you can slow down your warmup so much by using the heat. Also you can avert an engine overheat if you have a full grille block by cranking the heat in the cabin.

 

I was hoping there was a tech or someone with an extra block who could measure it for me. I should call Toyota service just for "fun"

 

The nipple that it came with turned out to be the correct size for the Prius Gen 1 block. I'm guessing that they are all standard thread sizes because the coolant tank heater I bought was generic.

It is a series 8000 Temro 1500 watt circulation tank heater. Made in Canada eh?... Hoser.

Go here: Engine Block Heaters
Click on the catalog link in the paragraph below for a PDF catalog. Go down to page 74... look for the 8000... Bada-boom.

I guess I should have updated.

The heater works incredibly well. It heats the block to operating temp in less than an hour. The Prius runs for about 40 seconds then goes straight into stage 4. It cut my FE on short commutes almost in half. Bonus cabin heat right after shut down. (to avoid delaying getting into stage 4) It's a bit tricky to install but hard core when it works. I hooked mine to a spare bolt on the block by modifying the mounting bracket a bit.

 

Yes. I installed it. The nipple that came with the unit was the right size. I used a ZEROSTART brand tank heater but the cords are not reliable. They seem to have poor electrical connectors at the unit which overheat and melt the boot doe to a poor connection. Unless they fixed the design, Kat's tank heaters may be better. You will need to "T" or "wye" into the coolant hose inside the engine compartment to complete the loop. It worked so well, it went into engine shut off after about 30 seconds. Helped a lot with FE.