Constant bubbles from coolant bleeder, cold lower rad hose!

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Nefarious
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Constant bubbles from coolant bleeder, cold lower rad hose!

Post by Nefarious »

Hey everyone I have been testing this car for a few days now! Not sure which to tackle next.. Here's the situation.
Car has 265k KM (165k Miles), 91 KA24DE 240SX n/a still at this point.

Noticed the car was overheating on the way home the other day so I threw the heater on high and pulled over to investigate. Turns out the upper rad hose was very hot and the lower rad hose was cold. Not cooler than the top but I mean COLD like the thermostat isn't opening.

The radiator is brand new and I already flow tested it, there are no obstructions. The old thermostat tested fine, but I got a new one and tested that and installed it and the thermostat still isn't opening. This lead me to think there were bubbles keeping air against the thermostat pellet which cool it too much to open. I don't see any bubbles out of the rad cap, or out of the overflow tank, but there is a CONSTANT stream of bubbles coming out of the bleeder hole when i am burping the system. It isn't a bit here and a bit there, it is a slow trickle stream, enough to make a small pile of slightly soapy looking bubbles building up over the bleeder hole. I ran the car constantly topping up the fluid and revving it in the inclined bleed position for more than 15 minutes and on 3 or 4 seperate occasions now and still... constant bubbles.

If I put the bleeder bolt in, the coolant system will start to pressurize and slowly push the coolant continuously out of the rad cap when it is off. It has never done that before and I have never seen bubbles in the coolant before.

I have had this car for 10 years and bled the coolant system MANY many times over the years and never had a problem getting out air bubbles, it is not likely stuck air bubbles, it is continuously generated small bubbles that are emerging from the coolant bleeder. I put the car up on ramps pointing up, AND used a radiator coolant funnel to make a high point much higher than the rest of the system. So I know it is being bled properly.

Next I performed a compression test to see if exhaust is being forced into a coolant jacket. Dry test with throttle plate fully open and my readings were solid at 185/185/185/185. There is no cross contamination between the coolant and oil whatsoever, the car runs perfectly and there is no visible exhaust of any kind. Definitely no white vapour.

Doesn't this eliminate the headgasket as an issue?

I did notice the water pump has more play than I would think it should have when i rock the cooling fan back and forth. I can hear a slight clunk and there is some visible play in the water pump input shaft. Could this possibly cause flashing or air entering the system?

I have not yet had a hydrocarbon coolant test or a coolant system pressure test but I cannot see any visible leaks anywhere and the compression test tested perfect.

Wondering which direction I should go. Change the waterpump that has some play, or pay for a hydrocarbon coolant sniffer test and buy the parts to build a coolant system pressure tester? Which is the more probable cause of constant bubbles entering the system? Thanks
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by shift_down »

Pull the thermostat out and drive it for a week. If you have no overheating issues, then it's probably a thermostat issue. If that's the case, then cut the jiggle valve off the thermostat, and drill like one hole next to the original hole, it should solve the issue.
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by Nefarious »

K thanks for the info dude. I picked up most of the parts yesterday to build a coolant pressure tester. Just gotta pick up a tee today to tie it all together, so I'll check that as well just to make sure.

I'll test the coolant system first, for any pinhole leaks and then ill replace the water pump, NAPA has them a lot cheaper than I thought it would be so 40 bucks is good insurance anyways if im boosting soon. FSM states basically zero radial play for the water pump and it definitely has some like 2-3 mm at the edge of the pulley diameter which is probably 1-1.5mm at the shaft.

Once I replace the pump, if the thermostat still wont open, then I'll drill out the thermostat jigg le valve so the air can pass through better and then it wont overheat at least. Still stumped as to how air is entering a bad water pump. There is DEFINITELY air entering the system. I had the car inclined for over 30 minutes yesterday just topping up the rad and it was constant small soapy bubbles coming up out of the bleeder hole. Every HG test so far has passed.

Just trying to fix everything to working how it should before doing any route-arounds. I have had this car as a DD for 10 years and never had an issue like this!
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by shift_down »

Good idea, keep us updated, because I am having the same problem. But my solution was to just pull out the thermostat, and Ive never had any more problems.

good luck, and report back
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by S14wayz »

yeah cold lower hose usually indicates a bad thermostat staying closed not letting the coolant circulate. Do what shift said. Good luck
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by Nefarious »

So I got some more time for testing and figured out a few things. First I pressure tested the coolant system with the vehicle running to see if the coolant system was generating pressure. I found there was no pressure! So I pulled the new rad and the front of the motor apart and pulled the water pump. I noticed there was a VERY slight coolant leak out of the bottom weep hole but the main thing was the input shaft had lots of radial play.

I pressure tested the new radiator on its own and found also that the bottom drain plug wouldnt hold 13 psi. I bubble tested the whole rad and found only the lower drain plug was leaking. Even 1 psi was enough to cause bubbles.

My guess is that since the radiator was bleeding off the pressure and not allowing the coolant system to pressurize, the system was much more prone to air being introduced into the system. I think the large radial play in the water pump drive shaft was enough to actually suck air in through the suction side of the pump since the coolant system was at atmospheric pressure. I was reading online diagnosis websites and it is rare, but it is a possibility of a water pump with completely shot bearings.

Water pump will be in tomorrow so I'll re install the rad (with the newly sealed drain plug) and the new water pump. Fingers crossed, but I think this was my issue all along. I'm surprised I couldn't find any dripping coolant! Must have just been slightly weeping out and then drying by the engine heat. Anyways just thought I would throw an update on here. I'll update tomorrow when I put everything back together and see if this fixed the problem.
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by S14wayz »

nice hopefully that clears things up let us know
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by Pjay240 »

I had the same issue. I replaced the thermostat and its been running back at normal temps now.
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by Nefarious »

Well im at a loss now. The bubbles are still coming up. Replaced the thermostat, waterpump and radiator (they were all worn out anyways). Just resealed everything and made a coolant pressure tester. Cooling system holds 15 psi no problem. I used soapy spray bottle and bubble tested everything and no leaks that i can find now. It definitely had minor leaks before.

Put it all back together, bled the system and fired it up and there are still bubbles entering the coolant system. I bled the system for a good 20 minutes with the clutch fan removed (kept an eye on the temp and it never climbed past half way) and small continuous bubbles just keep coming up. I am really starting to suspect the head gasket now, even though the engine compression test showed 185/185/185/185 psi and the coolant system pressure test held 15 psi no problem. It's freaking strange. I have a felpro head gasket ordered in and a new set of nissan OEM head bolts... I think im going to take it in to a shop and have them run a cylinder leak-down test and a hydrocarbon test just to confirm before I start ripping the motor apart. I understand that drilling out the thermostat will help relieve the bubbles from the thermostat and allow it to open, but that doesn't explain why air is entering the coolant system continuously. Thanks for all the suggestions. I will do the thermostat mod anyways since it seems like it just makes the system easier to bleed anyways but im really starting to suspect the head gasket now.
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by Pjay240 »

Nefarious wrote:Well im at a loss now. The bubbles are still coming up. Replaced the thermostat, waterpump and radiator (they were all worn out anyways). Just resealed everything and made a coolant pressure tester. Cooling system holds 15 psi no problem. I used soapy spray bottle and bubble tested everything and no leaks that i can find now. It definitely had minor leaks before.

Put it all back together, bled the system and fired it up and there are still bubbles entering the coolant system. I bled the system for a good 20 minutes with the clutch fan removed (kept an eye on the temp and it never climbed past half way) and small continuous bubbles just keep coming up. I am really starting to suspect the head gasket now, even though the engine compression test showed 185/185/185/185 psi and the coolant system pressure test held 15 psi no problem. It's freaking strange. I have a felpro head gasket ordered in and a new set of nissan OEM head bolts... I think im going to take it in to a shop and have them run a cylinder leak-down test and a hydrocarbon test just to confirm before I start ripping the motor apart. I understand that drilling out the thermostat will help relieve the bubbles from the thermostat and allow it to open, but that doesn't explain why air is entering the coolant system continuously. Thanks for all the suggestions. I will do the thermostat mod anyways since it seems like it just makes the system easier to bleed anyways but im really starting to suspect the head gasket now.

i had to actually drive my car around after i bled the system to get the bubbles to work themselves out.
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by i_slide »

Not really on the topic but today I took my OEM thermostat out and put in an ISIS colder thermostat. In about 15 mins the ISIS thermostat was back out due to over heating issue's. I bled the system with the ISIS thermostat with my classic yellow funnel with no luck. I threw my oem one in and brand new!

But too the OP, like above said, if your needle is staying about halfway you should be fine to take it around the block a few times then recheck. (it worked for me once)
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by hotbox240 »

I've blown headgaskets and still had good compression. I would pull the head.
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Re: Constant bubbles from coolant bleeder, cold lower rad ho

Post by Nefarious »

Well I decided to try and drive the car to see how it runs now that I replaced the main coolant system bits. It's actually running perfectly and not overheating anymore! No over flowing of the coolant res anymore! I still smell a very faint smell of coolant here and there in the engine bay when i open the hood but only when i have run the car hard for a while. the coolant level has been solid for 2 weeks now, no dropping level. The hottest its been is 25 celsius so far and no overheating in even stop and go idle traffic in town. Stays right at the half way point. I notice the temp climbs quickly to full but never deviates past the halfway point.

I think once my university diploma is done at the end of the month, I am still going to pull the motor and do the timing chain/headgasket/new frost plugs and adjust my out of spec lifter shims and possibly main bearings while im in there. I have to remove the oil pan anyway to weld in the oil return bung for the turbo so I think I'll just pull it and do it right the first time.

So far so good though, the 240SX is back to DD duty and has been running like a champ.

I figure with the compression numbers that I have, my engine is pretty damn healthy. I took it in for Aircare SMOG test a couple months ago and it passed better than most new cars. 3 columns of tests hydrocarbons, carbon monoxide, and oxides of nitrogen. I passed with 0, 0, and 1 in the columns where hundreds or thousands were the max passing numbers. The guy doing the test ran it twice cause he thought the machine broke.

I know it's off topic, but with an engine in the health that mine is, if I'm doing this much work restoring it for turbo application, would it be worth it (cost wise) to put in new rings and (forged) pistons if I'm only planning to run 300 lb ft. torque? I am running Nismotronic SA in an Infinity G20 Ecu (for maximum I/O) so tuning is not an issue, just wondering on reliability issues if the dollar is worth it for new pistons at the same time if I am only aiming for the 300 torque point as a daily driver. Too much more and my other half wont be able to drive it and how else will she drive me home from a night out otherwise! haha. This car is strictly fun/street car with maybe occasional auto cross duty but not a race car. Would rather spend more money on fixing the body up and restoring the little rusty spots at this point honestly.
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