bhg or bad rad cap?

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89supra7mgte

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Sep 20, 2009
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Ok so i took the car out stayed out of boost most of the time, just a few little 3rd gear pulls. Got home found that overflow has not overfilled but raised about an inch or so. First thought BHG:( I checked oil, good. Pulled plugs, Good. The temp gauge never got out of the optimal range, factory has no numbers so i put a thermometer in rad fins, might not be most accurate but only read 190 max. Fan is set to come at 195 and cycles at 185. Working properly could hear while driving (kinda loud) Is it possible to have bhg with no running problems or overheating?

I do not have block tester or compression tester handy are there any other things i can check? I am going to take cap to have it tested and hope thats all it is. Thanks in advance
 
thedave925

thedave925

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water does expand which would explain filling the overflow a bit prematurely. if you don't drive till the next day, the cool night should pull some of that back in.

A bad rad cap would begin leaking as the coolant temperatures raises, needlessly filling the overflow. Also, since the cap doesn't hold pressure, when the car cools the cooling system no longer has vacuum created to pull back in the fluid pushed into the overflow reservoir

OEM headgaskets don't normally pop suddenly unless your boosting constantly, like up a long grade. It is possible to have a slowly failing gasket that takes months to become obvious.

You can rent a compression tester at places like autozone/chucks/checkers. A block tester is probably the way to go, and there is also a kit to test the coolant for contamination as well.
 
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89supra7mgte

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Compression is good, i did borrow the tester from checker while getting a new cap. Installing a new temp gauge as well so i know the temp and not guessing by where the dial points?

Yeah what are you stunned about?

I have not been boosting the car constantly, just every once in awhile and not to full boost only like 4-5 lbs. Dyno is the only place car seen higher boost. After gettin my numbers i decided to take the boost down to be safe (stock)
 
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89supra7mgte

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Ok so turns out it was just my cap being bad. Yes i do know the reason of the expansion tank, maybe i made my post out to be more than what it really was. Been awhile since i drove the car (mods) and just caught me off guard. By bad cap i mean would not hold specified psi, so would release more coolant when warm/hot.

Jet i am not sure if that is a compliment or not? Error in my part
 
Last edited:
jetjock

jetjock

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In a way it was. Not like you to make such a mistake but hey, stuff happens.

Point is the system is designed to be kept completely filled at all times and without the pressure valve opening during *every* run to temp (along with the cap's vacuum valve opening during cool down) the hydraulic pressure would burst something.

Therefore it's normal to have the level in the tank rise and fall with the amount varying only by season/ambient temps. Course, for this to happen the entire "overflow" path from the neck to the suction screen in the tank must be air tight. Lots of folks ignore that path and then wonder why they always have air in the system.

The cap isn't supposed to be routinely removed btw. People do it but coolant is supposed to be added at the tank. The system should normally remain sealed. Removing the cap too often can cause more problems than it's worth.
 
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89supra7mgte

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Awesome thanks for that info. guess i never noticed it was alot cooler out last time i drove it. and today was like 100 or so. And if ambient temp may have an affect on it that may be my reasoning for such change.

Giving advice and helping others seems to be easier than fixing your own errors or problems, atleast for me lol.

I installed the new temp gauge and it is either way slow or my car really doesnt get that hot. Factory gauge reads half new reads 120-130. Thermometer in rad reads 160.
 
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89supra7mgte

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Its official no bhg. Car actually does not get hot either. New gauge reads 170-180 t-stat housing block side reads same verified. I am assuming that the external temp is within 10-20 degrees of actual coolant? chime in if this is incorrect. "expansion tank" working as explained to me prior, but is now at proper level. Think i was just expecting the worst after build up. But very glad its not. Thanks for all your help guys
 
thedave925

thedave925

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Everything is nerve wracking after major work, Congrats on everything panning out fine.

Question though, where'd you mount the temp sender for the new water gauge?
 
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89supra7mgte

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I mounted the temp sender in the location of the ac temp sensor (Radiator side of t-stat housing. No more ac system) I am going to relocate it and use a mech gauge being this one is electric and took a digger already.

I have a new issue that arrived today, not sure if it was an air pocket or what but pisses me off. Gauge started to read about 230, was not puking coolant or anything unusual, fans were on also, expansion tank had risen again but not overflowing. I decided to take a more thorough look at the cooling system with what i have at home. ran the car at about 1300rpm for about a half an hour, no pressure in hoses? Gauge at 220 pulled cap not psi installed thermometer coolant was right around 205 or so and would cool off when fans engaged. I could see the coolant flowing in rad was not leaking or losing any.

My question is what will cause no pressure in cooling system, with no external or internal leaks? I am thinking the t-stat might be culprit. not opening causing higher than norm temps and now being stuck open causing no pressure? Any ideas?

The mech gauge will be installed tomorrow in location of factory gauge sender, for more accurate reading. Will posts results when done.
 
Nick M

Nick M

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89supra7mgte;1585257 said:
My question is what will cause no pressure in cooling system, with no external or internal leaks? I am thinking the t-stat might be culprit. not opening causing higher than norm temps and now being stuck open causing no pressure? Any ideas?
Click to expand...

A leak. Pressure is constant in an enclosed system. A leak will drop the pressure. Your other choice is you don't have enough coolant.
 
Dirgle

Dirgle

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Also to note if you did take the radiator cap off and air got into the system, as the system heats up the trapped air may push out more fluid than normal into the overflow. It may take one or two heat cycles before all the air has been purged from the system.
 
thedave925

thedave925

Since 9/16/05
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89supra7mgte;1585257 said:
I mounted the temp sender in the location of the ac temp sensor (Radiator side of t-stat housing. No more ac system) I am going to relocate it and use a mech gauge being this one is electric and took a digger already.

I have a new issue that arrived today, not sure if it was an air pocket or what but pisses me off. Gauge started to read about 230, was not puking coolant or anything unusual, fans were on also, expansion tank had risen again but not overflowing. I decided to take a more thorough look at the cooling system with what i have at home. ran the car at about 1300rpm for about a half an hour, no pressure in hoses? Gauge at 220 pulled cap not psi installed thermometer coolant was right around 205 or so and would cool off when fans engaged. I could see the coolant flowing in rad was not leaking or losing any.

My question is what will cause no pressure in cooling system, with no external or internal leaks? I am thinking the t-stat might be culprit. not opening causing higher than norm temps and now being stuck open causing no pressure? Any ideas?

The mech gauge will be installed tomorrow in location of factory gauge sender, for more accurate reading. Will posts results when done.
Click to expand...

Thats too bad about the first sender eating it.

I noticed you didn't say anything about bleeding the cooling system initially after all the work done, so maybe following what Nick says is that there is still air finding its way out.
What is the condition of the heater core and its' seals? The smallest leak there (i.e. occasional drops in the HVAC catch tray that only a good nose would detect) would allow air back into the system.
 
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