Overheating after installing BEGi reroute on a used engine
 

I just swapped in a '96 engine into my '95, I decided to install a BEGi spacer and kia thermostat cover at the same time. Engine runs great, but the coolant is acting as if the thermostat is not opening, I have had that happen to me in the past and it's acting the same way. The thermostat is fairly new, I doubt it's defective, but if i can extract it from the back of the head I will test it in boiling water again. It'll overheat quickly and boil coolant in the overflow container. I have the thermostat sandwiched between the kia thermostat cover and the begi spacer as instructed.

Is it possible to put the thermostat in backwards under the kia cover and have it not open properly?

I am using the big GM hose to route to the upper radiator hose, and have verified there are no obstructions or kinks in the upper or lower radiator hose. The engine is a new-to-me used engine that has sat unused for many months, I guess it's possible that some water jacket is blocked maybe.

Any other ideas of what is causing my overheating besides a stuck closed thermostat? Could it be a gigantic air bubble, do I need to prime the long upper GM hose with coolant?

Are your fans working? System clogged?

Yup I don't have A/C, the single fan on the left of the radiator is working. It is definitely clogged with something, because it acts as if no water is going thru radiator. I have sorta narrowed it down to either the thermostat not opening , a clog in a water jacket or coolant carrying hose, or a big air bubble in the coolant system. I am really hoping its an air bubble, I may pull one of the turbo coolant hoses and hold it above the level of the head and pour in more 50/50 coolant to try and pack the head and upper radiator hose full of coolant.

I don't think is a bubble. The water pump will create enough force to circulate the water. A bubble in the system could create an issues once the system is pressurized and at high temperature.

Take the tstat off and see if you get flow, take it from there.

Yup I am with you on that, eliminate the tstat to see if that's the culprit. But the more I read the more likely I think it may be an air bubble, it seems fairly common to have air bubbles and overheating because of it right after you install a reroute. Looks like I need to "burp" the system which i haven't done yet. Also I have my upper GM style return hose dropping lower below the head than most people I've seen, seems this route may add more bubbles initially.

Burping the system: https://www.miataturbo.net/engine-pe...-issues-58740/

[edit] I ordered a Lisle 24610 spill-free funnel to help purge the coolant of air, I also plan to park the car uphill on my heavily inclined driveway. I may also crack the seal on the blocked off front filler neck to purge air trapped up high in the head.

It is possible to install backwards, make sure the wax bulb is facing the engine.

I hope the wax bulb means the side of the tstat that has more depth with the spring on it. I should elaborate that I am 99% sure I installed the tstat the same way it was mounted on the front, with the thicker spring side recessed into the begi spacer towards the block.

Pull stat. If needed, you can run system without stat to prove whether that is the problem or not (it should take a LOOONG time to register a temperature). More than likely it is.

Is this a recurring problem, or did it just overheat once? I've had several times I've replaced the coolant and it overheats immediately after. I've gotten to the point that the first time after a coolant change I drive it until it comes to temperature (10 min or so), then I park it until it cools down and it will be fine after that.

If it's only done it the one time, go drive it again and see what happens. Just keep it close to home so you can get back if needed. That thermostat is a major PITA to get to with a reroute, I'd hate to think you're pulling it out for nothing.

I have no tsta and it doesn't take that long to warm up. It comes in handy during the summer.

It's only happened once, right after a 12 hour day of reinstalling the engine and starting it up for the first time. I drove the car for a leisurely 5 minutes, was really pleased with myself and turned the car off to hear that the coolant in the overflow was boiling. I didn't have my laptop with me to plug into the MSPNP2 to see what the actual temps were but when I restarted the car a few minutes later and let it idle the dash temp gauge climbed up to about the 1 o'clock position in about 3 minutes. I decided to turn the car off and call it a night at that point after the long day.

When that happens just open the radiator cap after a few minutes to burp it. Sounds just like bubbles.

Wow, that's a lot different from your first description!

Are you sure your fans are working? I had something similar happen to me I checked everything until I realized the fan was dead. So I manually wired it :)

Turns out it was a lot of air in the coolant system, I used the Lisle 24610 funnel to burp out every last bit of air and now the car idles all day long at ~189º now. I think just letting it cool after the first warmup got most of the air because the radiator was pretty low when I opened it cold today.

Thanks for adding the recap. Makes for a more useful reference thread. Glad you didn't have to pull the T'stat.

xkcd is always relevant.

Thanks for not being that guy OP.