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Coolant puking, normal temps

J

jeddins

NAXJA Forum User
Location
San Diego
87 Cherokee pioneer, 4.0, 4x4

My dash gauge never reads over 160 although IR probing the engine shows normal operating temp. anywhere between 190 and 220 depending on where you probe. Water neck is pretty solid in the 190s. I replaced the factory closed tank with an aluminum version with a 16lb radiator cap on it. It still just randomly pukes for no reason. I suspect the dash gauge doesn't work but the fact taht it's puking makes me think there is more to it. Compression test is good, no water in oil or oil in water. Stock 195 degree thermostat. I haven't been driving it much lately but the last time I did it seemed to boil over pretty frequently for anything other than regular low stress highway driving. Anybody seen this?
 
You have 1. a closed coolant system with 2. an open coolant system radiator cap.

The open system cap allows the expanded coolant to move out to the coolant bottle, then as the system cools and creates a vacuum it allows the coolant to be sucked back into the radiator.

Your pressure bottle does not allow that. The charm of the closed system is that all the pressure and expanded coolant is retained in the system.

Your radiator cap is for an open system. You will need to put a heavier cap, or a non-vented cap, on your brand-new aluminum pressure bottle to restore the closed system.
 
yep, had the same problem and i put a 20lb cap on my 89. it works great now, also don't fill the reservoir all the way up, only halfway. closed systems need air to allow for the extra compression, it compacts easier- like a cushion
 
The radiator cap should not be a problem, unless it the return flow inner valve is not spring loaded to close (I have seen some that are not).

I have a hybrid with both style caps on a closed Renix with no problems. Sounds like you overfilled the bottle. The bottle needs to be half air, half coolant to work properly. You might have a bad cap?
 
Ecomike said:
The radiator cap should not be a problem, unless it the return flow inner valve is not spring loaded to close (I have seen some that are not).

I have a hybrid with both style caps on a closed Renix with no problems. Sounds like you overfilled the bottle. The bottle needs to be half air, half coolant to work properly. You might have a bad cap?
Click to expand...

I think Ecomike has the upper hand on this one. With the correct amount of air space in the tank the coolant should not expand enough to come out.
 
Factory expansion tank cap is set at 15 psi nominal (14-18). It wiill allow relief when it gets over a certain pressure. One of the things that drove me to change to the aluminum was that it overheated and blew off the cheapo plastic stocker. Then the threads got weak and it never sealed up.

The puking (or high system pressure) was there before the expansion tank was changed. When I fill it up I do only fill halfway. The current cap is a 16 lb relief. Functionally this is no different than the stocker except for the fact that the aluminum won't expand like the plastic. So you're giving up a small amount of expansion volume. 15 psi isn't much though and the stocker would start puking before any appreciable volume change. Cap on radiator or cap on expansion tank the system must be vented when there is an overpressure.

The question to me is what is causing the drastic overpressures? Is there a valve somewhere that get's clogged? The t-stat is new. I've parked facing down and quickly removed and reinstalled the temp sender to let any trapped air escape. Are these motors bad about air getting trapped?

I did trouble shoot the gauge this evening. The sender is dead on on the resistance but the gauge isn't reading correctly. Just to be sure I'm going to hook the gauge up to different resistances to make sure it's not reading correctly. But I do probe everything with the IR gun and never get anything over 220. Usually right at 195 on the water neck. I'm totally stumped so far.

I've never pressure checked it, but when it's puking in the parking lot it's safe the say that the system is >=16 psi. The only water coming out is at the cap. I've looked all around for other leaks and never found anything. I will do a pressure check this weekend though just to rule that out.
 
I have converted two renix rigs to open with no issues what so ever. I admit that when I did the change overs I to the 95 set up or so I replaced everything I could minus the blocks and the freezeplugs (and blockheaters). If the guage sensor at the back had increased resistance in the wiring or connections would that not cause an improper reading. When you filled the block and radiator did you burp the system at the guage sensor? Also I still do drill a tiny hole in the theromostat to assist in the bleeding.
 
I'm thinking about pulling out the t-stat and drilling a hole. Maybe going with a 180 also. I have bled from the sender though with the sender being the high point. Maybe there's some blockage somewhere.. this does have a zillion miles on it.

As for the gauge I'm going to check this weekend for funny discontinuities between the gauge and connector. Hopefully I get lucky, I REALLY don't want to pull the dash out!! When I trouble shoot the gauge by applying it to varying measured resistances I am going to wire up directly to the back (or as close as I can) to the gauge.
 
Based on what I have read in this thread, my best guess is the radiator is plugged and scalled up, and or you have a head gasket leak blowing air into the coolant system during compression. My money is a head gasket leak pushing air into the coolant and creating the over pressure. Have you pressure checked the neck on the bottle and the cap itself to make sure they are holding 16 psi?
 
Yeah, I'm sort of not willing to admit it but that is what I am thinking. Not having a temp gauge takes away some good info, but if I trust the pressure is good to 16 psi that puts the boiling point at 250-260 or so. Probing around gives 190-220. Shouldn't be boiling at all. I'm still going to trouble shoot some more. Compression test is good. Need to do leak down.
 
Pressure test the cooling system too!
 
Okay, given this car has had a history of overheating before I changed tanks I still need to do a leakdown and pressure check. BUT-

I did have a vented cap on it (??? it was the cap I received w/ the tank and never checked). I thought they were all vented, i.e. they all flow back from the overflow tank through the bottom of the cap (take your cap off and pull the little poppet on the bottom, I assumed that was what vented meant). Apparently a VENTED cap has teh same poppet relief but it isn't spring loaded. There are two types of reliefs.

SPring loaded- Car shuts off and cools. As it cools a vacuum is generated in the engine and the poppet opens. Teh coolant in the tank gets sucked back in.

Weighted- Poppet is actually held open with a weight. When the pressure in teh system rises it forces it closed. This system allows air to be bled out during low temps and reduses the pressure on the coolingt system.

So when I shut off the motor and it had a while to cool the poppet would start to flutter and the car would puke.

So I mistakenly always thought that a "vented" cap referred to the lower poppet that allowed coolant to come back in. Vented actually refers to weighted vs. spring, but makes a huge difference in operation. But if you were to run a recovery tank I don't see why you couldn't run a vented cap and it actually seems like a good idea. So those radiator caps with the bottom popper dangling there aren't broken, they're vented!

So my apologies to the first post that mentioned the vented cap. I always thought I knew what was meant by vented cap but just proof that we're always learning.

AS for the temp gauge, it's hosed. I hooked it up straight to a bunch of resistors and it's not reading anythign close. Off to the junkyard I guess.

Thanks for all the replies guys!! I hope somebody learned something. Maybe you all already knew the difference between the two types of caps but I didn't. Check out thel link below for all you wanted to know about radiator caps.



http://installer.aed-inc.com:8191/Stant Technical Info/TempTalkRadCap_4.htm
 
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