Coolant Pressure Test Questions
 

Hey Guys,

I have been having some issues with my car overheating while at higher speeds like on the interstate. Around town my car runs just fine and I don't see any high temps, but once I jump on interstate at a sustained higher speed my temps start climbing. I have a Koyo rad which has been flushed and an FMIC completely ducted. This has been an issue for two summers now.

I just got the car back from storage this weekend. I did two complete flushes of the coolant system and changed the oil. Oil looked fine and it didn't seem like there was any coolant in it.
The car fired right up and didn't smoke much. It was a little flooded, but hasn't been started in a couple of months.

So last night I went and rented a pressure tester to see if I could find any visible leaks.
I have been suspecting a coolant o-ring for a while now, but I don't know for sure.
Coolant is not always sucked back from my overflow, so I though I may have a leak somewhere.
There isn't anything visible, so I grabbed the pressure tester.
My car ran fine all day yesterday. I drove it back and forth from work, sat in a line at the bank, and I didn't see a temp over 90 deg C according to my PFC.

So I let the car cool down after work and opened the filler neck. Coolant was right where it was supposed to be and the overflow was at "F". So I placed the pressure tester on the filler neck and pumped it to about 13 to 15 psi. Almost immediately it started losing pressure. I couldn't find any visible leaks. So when it reached 0 psi I removed the tester and it was about 1/2 cup low in the filler neck so I added coolant. Did the test again and the same results. I ran the test three times, topping off the coolant each time.

Without finding any visible leaks I figured the coolant must be pushing into my engine.
I jumped in the car and it fired right up with a smooth idle and not a puff of smoke.
The car idled in the driveway for about 5 minutes and was only at about 50 deg C.
My brother jumped in the car and I told him to go for a quick drive around the block and keep an eye on the temp. Within 3 minutes I got a call from my bro saying it spiked to 115 deg C so he pulled over and shut it down. Ten minutes later it dropped to 100 deg C so I told him to start it up and get back to the house. Within 3 blocks the temp shot to 129 deg C before he made it home. SHIT! Coolant was spitting everywhere. Obviously there is an air lock somewhere and of course I forgot my Lisle funnel back at my parents where the car was stored. But it was running fine all day and it only overheated after I ran the pressure test which must have pushed air into the system somewhere but the coolant was only a little low in the filler neck after each test. Also, the filler neck adapter sat low enough in the filler neck to block the overflow nipple (I have the FC filler neck adapter / delete AST).

When the car cooled I topped it off and let it sit overnight. I haven't got a chance to dig into it anymore today yet.

But my question is, if it was a bad o-ring and the coolant was getting pushed into the engine shouldn't it have ran like shit and been smoking to beat hell? And if the system was leaking that quick I should be able to find coolant leaking somewhere, right?

Any ideas for my next step?

Thanks for any help, Josh

At 129C youve either blown it or close too it. You might have over pressurized the system if im reading correctly u forced air in with coolant still in the system.

Try flushing it the right way with the lisle funnel, heat on,etc. and check for overheating/bubbles.
Look into the thermostat and possibly not running one for the time being

If all else fails and you want to be 100% sure it was a coolant seal. Rip it down to a short block and use the pineapple racing pressure tester.

I'm trying to figure out how I could have overpressurized the system.
After my last pressure test I completely removed the tester and the coolant was about 1/2 cup low in the filler neck, so it was open to the atmosphere. Wouldn't any excess pressure just vent it the filler neck was open?

I flushed the system twice on Saturday with the funnel and didn't have any bubbles.
I might try replacing the t-stat, even though it seems like it was working fine all day yesterday before I tried the pressure test.

I agree about the 129C, scared the hell out of me.

Have you looked for "champagne" bubbles? Remove the filler cap and start the car and see if you see any bubbles. Also upon startup see if coolant spits out of the filler neck. If so, then the engine is pressurizing the coolant system and yes you have a coolant seal gone bad. 129C may have done one in anyways if the coolant temp really got that hot (no bubble).

On the pressure tester, did you verify the tester was not leaking at the connection to the filler neck? I use a spray bottle with soapy water to do this.

Your symptoms almost sound like a randomly sticking t-stat. I just recently went through all this and my car never overheated, but was loosing coolant and smoking a little over about a two week period. Then I pressure check the system and it checks OK, only lost a couple psi over an hour. I fire it up and it billows white, sweet smoke. Def a coolant seal gone bad. I break it down to the short block, turn the motor over by hand an more than a pint of coolant pours out of the front exhaust port... With no sweet smoke, I don't think you are consuming coolant in the combustion chamber.

this is what you don't want to see.

http://www.youtube.com/watch?v=lQ1yG...eature=related

Not sure about the coolant loss if you're not seeing any leaks, but do you have any type of under drive pulley? Also I had a similar problem with another Rx-7 owners car where the car would run hot on the highway and fine around town at low speeds. The problem ended up being the water pump even though it was not showing any signs of failure.

-Dan

Run the car with the Lisle attached to bleed air out of the system.

The tricky thing w/ coolant system pressure tests is that you need to somehow ensure that the pressure you are pumping in is sealed off from the line going to the overflow tank. If you did have an issue with a coolant seal, it would be a very tiny orifice that is leaking. Therefore the pressure wouldn't decrease that quickly. If it did, you would know it b/c the engine would indeed run like shit and you'd see a huge cloud of smoke out the exhaust.

I have ran the champagne test a couple of times with mixed results.
Over the weekend after two good flushes and a final fill with the funnel I wasn't seeing any bubbles. I also tried one of the Napa Block Tester gizmos that let vapor run through some blue liquid and if it turns yellow its exhaust. The Block Tester has vapor running through it, but only because it was not vented, but the color did not change. When using the funnel there isn't any bubbles.

As for the pressure tester, the tester went deep enough into the filler neck to where it blocked off the overfill nipple, so it shouldn't be losing pressure there. I did in fact get some soapy water last night and rubbed it all around the pressure tester and the filler neck to try and locate and bubbles, but nothing. That's not saying there may be a leak elsewhere. Im not getting the white smoke though. But I am wondering if there is a coolant o-ring leak if its small enough that only exhaust can enter the coolant, but coolant can't enter the engine because it may be sealing back up when the car isn't running.

I do believe there is some aftermarket underdrive pulley. I can't locate a manufacturer, but it was on the bad engine when I purchased the car. I had it rebuilt by Atkins and placed the pulley back on the car. I may try changing the t-stat and maybe the water pump this weekend.
I had a friend telling me the water pump impeller may be slipping at higher RPM's and not being able to keep up, which would make sense on the interstate when a sustained RPM is held for longer periods.

I still think its probably a bad o-ring, but before I tear it down for a rebuild I want to make sure.
I may try some disassembly this weekend and look for more leaks. Pressure is definatly going somewhere.

Thanks for all the help and inputs guys.
I really appreciate it. I just wish there would be somebody near who knew more about rotaries.
There isn't a mechanic around that will even touch it.

That's exactly what I was thinking. For as fast as the pressure was dropping there would have to be a 1/4" hole in the o-ring, and even after three pressure tests the car fired right up and didn't smoke one bit. But I must have displaced some coolant somewhere to make it overheat that quickly. I'm just not sure where else it could be going.

could it be that the underdrive pulley isn't snugged up against the belt so that it starts to slip at higher sustained rpms?

Is the air pump still attached to it? If not, does it have an idler pulley in place?

glad I read that comment scrub, i would be shitting my pants if more then 1/4 cup of coolant were missing. maybe when it happens it will just be my pump......... the inevitable...

I really would be surprised if you have an o-ring failure. At least the common one into the combustion chamber. If you were burning coolant, especially with pressure drop like what you are seeing on the tester, you would be refilling the coolant very often and smoking like crazy... I would think that also a pressure drop like that if not internal, would be a noticeable external leak.

Scrub's idea I really like and is a new one on me. (Thanks for the tip Scrub!!) Also, if you have the airpump removed, maybe you need the idler pulley to help create more friction on the waterpump.

Went single and air pumps is gone.
I don't have an idler pulley anywhere on the belt that goes from the main pulley, along side the water pump, and up to the alternator. But tension seems ok. But maybe its slipping at higher RPM's. The belt is fairly new and isn't hard or slick, so it should be grabbing. I have the Greddy blue pulley kit for my water pump and alternator.

Update

I had a chance to start working on the car again this weekend.

I noticed that the radiator cap had small air bubbles coming from underneath the sticker that was on top the cap, so I grabbed a new 13 psi cap to try out.

I got it burped out as good as I could without my Lisle funnel, I used a 2-liter bottle and tried my best.

Last night when I thought the system was full I let the car idle in my driveway for a good 10 minutes. Temps on the PFC got up to about 78 - 80C and then dropped to about 75C when the thermostat opened.

Left the car overnight, but when I checked it this morning I went to crack the radiator cap, but as I slowly moved it I could hear air or coolant bubbling into the overfill. Should the system always be pressurized? I would think that the next morning you could remove the radiator cap and it shouldn't be pressurized. This is making me wonder if the system is not pulling coolant back from the overfill.

Is this right? Should the coolant system always be pressurized?

This afternoon when I opened my radiator cap, it sounded like air bubbled into the overfill, but the filler neck was low. So I have been adding and burping up until now and it wouldn't take any more coolant. I siphoned out all the coolant in the overfill until the level was at "F".

Started the car up and it took quite a while to get to temp.
I had my heat on and the fans blowing max, but wasn't getting any warm air until about 50C. It held at 56C while idling for about 5 minutes and then started climbing.
Temp got to around 78C and jumped to 109C within a minute.
The overfill spit some out on the ground again.
Obviously there was an air pocket when the thermostat opened.

Now I have to let it cool to check where the level is.
It should in theory suck back coolant from the overfill, but there must still be an air pocket, but shouldn't it work out through the overfill?
Even if exhaust was entering the coolant wouldn't it work out of the overfill tank and then the coolant that was pushed out suck back in?
I am just confused on why any air in the system wouldn't work itself out into the overfill once the 13psi cap opened.

Sorry for all the dumb questions.

Also, I spun my water pump by hand to check for play.
With a good spin the pump would make one revolution and then "squeak" to a stop. There was coolant in the system at the time and the level would move up and down when I spun the water pump by hand. Is the "squeak" at the end of its revolution a sign of a good or bad water pump? There isn't anything leaking out the weep holes from what I can see.

One more quick note.
After 10 to 15 minutes I went and checked on the car.
The upper radiator hose from my thermostat housing to the upper radiator neck is flat. I believe that means there is a vacuum in the system, but it doesn't look like its sucking any coolant back from the overfill.

Thats from using the wrong radiator cap or a bad cap or the hose to the overflow is clogged.

Brand new 13 psi radiator cap. I can blow through the hose to the overflow, so I don't believe its clogged. Fluid flows to the overflow just fine.

Getting to the original problem you posted up, do you have the belly pan on the car? Sometimes cars will overheat at speed with no belly pan since the air will simply pass straight under the car instead of going through the radiator.

Dale

Yes sir, I have a belly pan that I made along with full ducting through the ic and the koyo.

Hey Guys, just an update.

I ended up purchasing the Pineapple Racing idler pulley, and a new T-Stat from Malloy.

Pineapple's kit is great. Fit and finish is very nice and it works flawlessly.
I think this is a great adder for the airpump deletion and there is plenty of room even with a large singe.

I changed out the stat and got the car completely burped out.
It ran great for all day Saturday until after shutting it down I heard a hissing under the hood.
One of my rubber caps that blocked off the lower nipple on the thermostat housing got a pinhole and was spraying out coolant. This was on the nipple that would have originally fed the AST.
I have it blocked off along with the AST deletion.
After the pressure was low enough I was able to remove the radiator cap and replace the rubber cap with the ghetto "bolt in a piece of rubber".

I then proceeded to refill the system and get it burped out.
It took several times of letting the car get to temp trying to get the thermostat to open before the coolant would start bubbling so hard that it would overflow from the Lisle funnel.
It seemed like there was an air pocket behind the thermostat and it just didn't want to open.
It finally did after about 10 different start-ups.

On Sunday I was able to drive the car around a little. Temps held at about 85 - 89C driving around my neighborhood. When I got back to my place I let the car idle for about 10 minutes to see if anything would change in temperature. After about 10 min the car was steady at 92C so I shut it down for the night.

Before calling it a night I checked the overfill bottle and the level was 4 lines above "F".
I made sure before driving it around that it wasn't above full. So in a matter of 20 minutes of driving around and 10 minutes of idleing the overfill level raised by 4 lines above "F".

Today at lunch I was able to check on the car again and the coolant level in the overfill only dropped one line. I cracked the radiator cap and it gave a little gurgle which sounded like air going to the overfill. The coolant level in the filler neck of the thermostat housing is low, but it didn't suck much back from the overfill. The overfill line is good, but tonight I am going to go through all of the other lines (turbo feed and return, heater core feed and return).
I have the line off the back of the thermostat housing that ran to the bottom of the throttle body capped off and also the line from the back of the engine near the fire wall that feeds the top of the throttle body also capped off.

I still think I have o-ring issues, but the symptoms seem to come and go. But my question is how quick should the coolant system get to 13 psi to allow coolant to run to the overfill, especially since it didn't even get real hot? The temp during driving and idling never got real hot so I don't know if there is still air in the system or if exhaust was displacing the coolant and pushing it to the overfill. But if exhaust was pushing out the coolant to the overfill wouldn't the exhaust also make its way through the overfill? I guess I am not sure why any exhaust in the coolant wouldn't purge itself out through the overfill tank and then the coolant wouldn't be sucked back into the engine.

Sorry for the novel. Josh

I think it sounds perfectly normal now. What exactly is the perceived problem?

Remember that fluids expand as they get hot. So the level on the overflow bottle will be higher if checked hot. Also remember that coolant contracts as it cools As the engine cools, it sucks extra coolant back in from the overflow tank. Often sounds like a bit of a gurgle after shutting down. AT least mine does.

The problem is that it didn't suck much back into the engine after cooling overnight.
And the level in my filler neck was low even though my overfill was high.
It seems like air is forcing the coolant out, but not sucking it back in.

I need to replace a couple of hoses to try and completely rule out any pinhole leaks that may be allowing air to re-enter the system as it cools and not suck back the coolant from the overfill.

But the gurgle sound was at lunch today when I opened the radiator cap.
The car has not been started in 15 hours, but the system was still under pressure.

So come morning, you open up the filler neck at the thermostat housing and see it an inch or so lower than full? Meanwhile, the overflow is at the Full mark?

You know that by opening the rad cap at the thermostat housing while the car is cooling down, you are introducing air into the system?

I can't remember if my car holds pressure in the coolant overnight. Maybe I'll check that tomorrow.