Overheating issue on KA rebuild - need your help

[OverBoost]

Guys, I have an overheating issue I just can't seem to solve. I have a recently rebuilt (less than 100 miles) KA24DE that overheats after about 15-20 minutes. It is completely stock except for a barely used Mishimoto SR radiator with crossover pipe and electric fans. It does have a new waterpump, new thermostat and new hoses.

I have completely bled the system twice, with the rad cap off, funnel in to watch levels and I made sure all air bubbles have come out of the system (also turned on/off heater in the car). It currently has 50% water, 50% coolant and I have also added Water Wetter.

When idling in my garage the temp gauge stays right in the middle where it should. When I close the hood and take the car around the block, it starts to creep higher and gets almost all the way to the highest H mark. The top radiator hoses are very hot but lower hoses are cool/light warm to the touch. The hoses also seem to be under pressure as they visibly expand when hot. There are no leaks/drips.

Could it be a bad temp sensor (near water outlet)?

ANY ideas would be very welcome as I am stumped. Thanks!

[burnsauto]

trying running no thermostat (not for a permanent fix) and see if that changes anything.

[ManoNegra]

Does the heater work fine?
you may have clogged water passages in the motor.
what was the condition of the rebuilt motor.
had a friend that picked one that had been sitting for a while at a yard
had the same problem you're having
when we took the motor apart and checked the freeze plugs
it had chunks of rust/grime in the passages

[OverBoost]

Thanks for the replies.....The heater does seem to work fine, it's blowing warm air. The condition of the motor was great when I rebuilt it. It was the engine that was in the car before it was rebuilt because of bad rings. The block was hottanked and had new freezeplugs installed by the machinist.

I have a feeling the thermostat is either not opening or not opening all the way. I believe it is a 170 degree thermostat and since the lower pipe is very cool, could it be that its not getting warm enough to open and circulate the water? If so I might have to upgrade to an even lower temp t-stat like a Nismo.

I will try removing the t-stat tomorrow and see if that makes a difference.

[initial_drifter]

If the upper hose is hot and lower is barely warm then You my friend have a stuck T-Stat

Ps. when bleeding the cooling system did you loosen the bleed screw on the housing of the upper hose? *the little gold bolt*

If not, loosen it and fill until coolant comes out in a smooth flow. Then add fluid if necessary

[chentes14]

i Had this same problem i replaced the water pump, radiator, hoses, thermostat,
and it would still overheat i just bled the system first i got a flush but they pressured flushed it, and then i bled it my self make sure u loosen up the the golden bolt and jack up the front of the car, run the car for 10-15 minutes with rad cap off and mess around with hoses that should work man.

[wangan_cruiser]

jack the car the highest u can lift it up that way its easier for the bubbles to go out than being a level pavement.


everybody's statement is true. u need to spend time to bleed ka's stubborn cooling system.


to check your t stat if its not opening. get a pan then put some water in it and boil it then watch if it opens or not. that way its easier to tell if your thermostat is functioning right.



and about the golden bolt, i never touched that whenever i bleed my cooling system.



and u dont need to run a cooler t stat. stock will be fine unless your car is boosted and track it everyday

[initial_drifter]

The bleeder screw is the highest point of the cooling system on a level ground so there is no reason to lift the vehicle

Most people overlook the screw which is probably why it seems "stubborn"

It won't be a mind blowing amount of bubbles that will come out but it's a good practice

All in all, it shouldn't take more than 30 minutes with cleaning up.

2 cycles is what I usually run the motor for bleeding

[OverBoost]

I have bled the system multiple times, ensuring there are no bubbles in the system, with a funnel in radiator neck and filled with coolant. I understand it is very stubborn to get all the bubbles out.

Last time I ran it after bleeding, the car got up to operating temperature, then I drove car around block and temp creeped up. When I brought it back into the garage, the temp gauge showed it was on H, all top rad hoses were very hot to touch and were bulging. Top of radiator was very hot, but bottom of it was cool to touch.

I can't see after bleeding this system repeatedly that air bubbles could still be causing this. I think the T-stat is not opening or is not opening all the way. Keep in mind I did not have this problem before the rebuild with the old crummy OEM radiator.

Also, since it's an aluminum radiator, at twice the stock thickness, I am thinking the coolant coming out of the bottom of the radiator into the t-stat is just not warm enough to cause the t-stat to open properly.

I'm going to boil the t-stat tomorrow and see if I can ensure it's opening and closing properly.

[CrimsonRockett]

Are you still using the Mishimoto radiator cap?

Buddy of mine was having overheating issues.

We tried all sorts of shit with the same result.

Finally changed out the radiator cap for a Nismo.

No overheating problems since.

[s14l0v3r]

Try running without the thermostat and make sure you have enough coolant in the system. Then test the thermostat to see whether its opening at 170F(if its OEM). If its opening and ur still overheating..i would say check for leaks, even though everything is pretty much brand new. I had a similar problem and couldnt figure it out..saw no leaks but would always be low on coolant after about a week or two..then found a leak but it would always boil and evaporate before it could drip to the ground. So dont rule out everything right away. Let us konw how everything goes.

[OverBoost]

I'm still running the Mishimoto radiator cap and I doubt it is the problem because the system is still holding pressure. This is apparent from the bulging upper hoses when running hot and the rad cap feels solid when tightening it down, but it's worth a shot with another cap to see if that is the issue.

I will try running without the t-stat installed and see what happens then. I'm also going to boil test the t-stat and make it is opening properly.

I'll keep you guys posted, thanks again for all of your suggestions.

[brian3676]

you said its a new water pump, sometime they mess up the pumps and put an inverted propeller on it so its flowing back words, happend to proble 1 out of ever 1000 pumps, but you could have got that 1

Also you said you open and close the heater core..... keep it open, but keep the auctual fan its self off

[silpena]

try replacing the cap, ive heard they suck and leak a little pressure. I hate using the bleeder bolt, ive allways just filled up the radiator to the neck and massage the uppper and lower hose and force th bubbles through the t-stat if its being really stubborn. works like a charm and i usally get it all out the first time bleeding it. Takes about 10-15 min. Sometime i let it climb up then squeeze and massage the lower hose to force it to open up and with the heater on of course.

[OverBoost]

Ok, tested a few theories today:

Test 1: I got a new radiator cap: it is a cheap Stant cap, I didnt want to drop $30 and wait a few days to get a Blitz/Nismo/HKS, etc. Put that on and car still got almost to the H on temp gauge after getting to operating temp and driving around for a few minutes.

Test 2: I removed the thermostat and performed a boil test on the stove. T-stat starts opening at 170 degrees F and is fully open at about 195 degrees F, performed this test twice to verify.

Test 3: I ran the car without the t-stat in it, after I fully bled the system. The car did NOT overheat, but the temp indicator did not get all the way to the middle (operating temperature) it was on the second or third mark.

So, do I put this t-stat back in or order a Nismo t-stat (lower opening temp). Or do I have a bad temp sensor or gauge? I am aware the stock temp gauge isn't very accurate, but before the rebuild, the temp gauge did not do this.

What do you guys think?

[Charlie]

How cold does it get over by where you live? That can determine if you should run a t-stat, or if you really care about mpg. IIRC if your car isnt running at operating temp you will get lousy mileage. I run without a t-stat and seems fine to me.

[OverBoost]

The lowest temperatures can get where I live is in the low to mid 20s in the winter. However, I do not feel safe running without a t-stat because without it, the engine will not be able to get fully warmed up before driving and thus could cause damage to engine internals over time.

After doing some more reading the temp sensor COULD be faulty and since I am not sure if it has ever been replaced, it could have deteriorated over time. So I will order one of those anyway, but I doubt that is the root cause of the problem.

[OverBoost]

Update:

The car is not overheating anymore.

Here is what I did: replaced the coolant temp sensor in the upper intake manifold. When I removed the old one it seemed corroded and was probably the original (ie: 17 years old) unit.

After I replaced that, I put the thermostat back in, but before putting it back in, I cut off the "jiggle valve" on the t-stat. It's designed to let air through when you are bleeding it, but I have heard it sometimes can be a problem so I cut it off, leaving a small hole in the t-stat which aides in bleeding.

After bleeding the coolant system and test driving it for 20 mins, the temp needle never got above the middle range of the temp gauge and the car drove great without overheating.

Tip for others: If you are rebuilding your engine or are experiencing cooling issues, replace the temp sensor since it's only a $15 part and will save you some headaches down the road.

Thanks for everyone's help and suggestions, you guys got me in the right direction and helped fix the problem.