outersketcher

I've got my newly milled engine from the machine shop. completely dry of coolant and oil of course. Filling the pan with oil and priming the oil pump is obvious. But what about the coolant system?


I'm thinking I should wait on installing the thermostat and housing untill I have the engine and radiater installed back in the xj. Put a long-neck funnel into the thermostat housing hole and pour in coolant till It almost drips from the thermostat hole. Then install the thermostat and its housing.


I'm worried about trapped air. The instructions for the newly built engine tell me to start that engine and KEEP IT REVVED to 1200 RPM for the first 30 minutes.


Thirty minutes is a loooong time. You can do a LOT of damage to an engine in thirty minutes.


The thermostat I have does NOT have an air bleeder hole in it. I've read posts and seen youtube vids of people driling a 1/8" hole in their thermostats to allow trapped air to escape. I plan to do the same..


Is that a good idea? I'm worried about getting all that air out of the newly installed 4.0


I appreciate your comments. thank you.

BooGTS

I've drilled a 1/8" hole in thermostats before, seems to work and there is no real downside. 1/8" is not big enough to matter.

BlueRidgeMark

1. Stop worrying about it.
2. Drill, or not. Whatever. If it needed it, the factory t-stats would have it. It's kind of like using 1/0 gauge battery cables or throttle body spacers. It's all the buzz with the kids, but it's not actually doing anything useful. However, it won't hurt anything.

Fill it normally and do your break-in. Just stay with it and keep an eye on the temp gauge. No big deal.

Tbone289

^ good advice, especially #1.


I personally would just test the thermostat in boiling water before I installed it, but I always do that.

PatHenry

x3

I don't see why you couldn't basically bleed the cooling system while you're doing the break in. Just have an assistant keep the rpm's up while you keep topping off the radiator and then once it's up to temp and not taking any more, put the radiator cap on and keep an eye on the gauge.

I have a plain old stant 195 (without the hole) in my 95 and haven't had a problem with it.

investinwaffles

You kind of have to bleed the system at the same time, as soon as the tstat starts to open it will suck the coolant into the block.

Just keep the rad cap off until it stops taking coolant, fill the reservoir past the high mark and keep an eye on it.

Drilling a bleed hole is a good idea too, as is testing the thermostat before installing it

When filling, squeeze the rad hoses to try and burp some air out of the system before you crank her up. Prime the oil using the distributer shaft key (I like to prime 2-3 times) and make sure you use a good break-in oil with ZDDP
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5-Speed

You can also use the heater core lines to fill the block. They dump water in on the back side of the thermostat.

robertj

It's a waste of electricity to drill a hole in that thermostat, but guys put cardboard in front of their radiators too so what do I know.

fb97xj1

If there is no hole, add one. Position the hole in the 12 o'clock position. Makes it easier for any bubbles to pass. Thats why the factory uses a jiggle valve. To let the bubbles thru.

outersketcher

I hadnt considered actually testing the thermostat itself.. you seriously just drop it into a pot of boiling water?. And watch for it to open?

I think I'll drill the hole anyway.. on the grounds of "hey it won't hurt." And I had completely forgotten about the heater hoses.. thats right.. a good way to introduce coolant to the engine block when everything else is all buttoned up.

Tbone289

Heat water with the thermostat in it, and use a thermometer to show the temperature of the water. The thermostat should start to open at the specified temperature (195), and should be fully open by the specified temperature plus 15 degrees (210). Obviously, the water won't be boiling at this point.

BooGTS

The factory puts "cardboard in front of the radiators" in the form of shutters. It helps with warm up time and aero. In the dead of winter blocking off my radiator keeps my trans temp above 100F (have a gauge) so I do it too.

robertj

Considering a properly functioning thermostat doesn't open until 190+ degrees and allow coolant to flow through your radiator, explain to me how that cardboard in front of it does anything? Maybe it's the hole you drilled in your thermostat. If you're concerned about transmission temperature, that's another story and probably overkill.

outersketcher

These are salient points to make. For a running vehicle.
But remember, I'm talking about starting up a BRAND NEW REBUILT ENGINE. Bone dry from the machine shop. Still glooped with engine rebuild grease.

No matter how you go about filling the radiator and even pouring some coolant via a funnel into the block itself. You're going to have HUGE amounts of air in that block. I want that air OUT of the system and away from my newly milled head as fast as I can. If drilling a hole in the thermo will help me accomplish that goal. It might be a good idea.

5-Speed

Having just done the exactly same thing that you are doing (new engine), I will let you know how I did it because I was worried about the same thing. We all know you need to break the cam in right off the bat and turning the engine off partway through the process isnt the best thing to do.

Step one - dont add any coolant, use straight water. First fill is just for cam break in and for driving around to verify everything is good.

Step two- fill with water through the radiator like normal until full.

Step three - (this is the messy part and the reason for no coolant) leave radiator cap off, pull a heater core line off, attach hose to heater core line feeding water into the block. Turn the hose on and let it fill the block. Once its full, it will start over flowing out the radiator. Keep the water flowing until you see no more air bubbles coming out of the radiator.

Step four - if no water came out of the disconnected heater core line while you were filling it on step three, you need to fill the heater core with water.

Step five - put heater core lines back on. Top off radiator if possible.

Step six - Fire it up!

Once you are done breaking it in, dump some of the water out and fill it with coolant.