Coolant

VET88M

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Jul 10, 2015
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Got home from work parked, notice little steam coming out of hood, temp gauge reads fine, nothing odd going on.

open the hood and i find some moisture around, on closer inspection i blew the fuckin overflow sensor out the bottom of the tank.
now for all you guys quick to jump the gun and say BHG over pressurizing system i want to make the statement that there's no signs prior, no mixing etc. and heads been redone awhile ago.

my main concern is i took the radiator cap off. both seals still look good but there seems to be a lot of play/looseness between the spring and the copper capping, is there supposed to be this play for this cap or is it supposed to be nice and tight? could this play cause improper function leading to cause the pressurization? or should i move toward inspecting other possible issues.

first time its done this like is said i have
no missing
no power loss
no tail pipe fumes (jar test)
no mixing (either)
no hissing at the cylinders
etc.
 

VET88M

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coolant flush and burp seemed to solve most of the issue, still over flowing a little bit not bad, gonna buy a new cap Friday, should solve the rest of the issue. pretty sure 24yo cap its time for a new one.
 

VET88M

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no what was happening is the bad cap was allowing air in, which air in coolant system as you know creats hot spots which will actually cause the fluid to boil esspecially so older fluid. 2 days of hard driving since i changed out old fluid and cap and its still running perfect no boiling and no over flow
 

Roger UK

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I also doubt that the cap is your problem, I'm afraid.

When the HG starts to fail on these engines it usually starts leaking INTERMITTENTLY.

It can be fine for a couple of weeks . . . and then one day you will get pressurisation and tons of coolant pushed into the overflow bottle. When this happens, the temperature gauge will usually be normal (unless you keep driving with low coolant).

Let it all cool down and the next day it can be fine . . . so kid yourself that it's not a BHG after all. But the gap between each occasion will get closer and closer.

Normally the 7M HGs start leaking between the waterway and a cylinder (hence the pressurisation) . . . if you take the head off early enough the gasket will normally show no sign of damage . . but trust me, it's been leaking!

Rarely does it start leaking coolant across to the oilways (hence seeing no emulsion in your oil) . . . but if you leave it, it WILL . . . and one bit of coolant in your oil will normally result in Big End Failure on the 7M engine !
 

VET88M

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Like my previous message stated, it was the cap. Its been over a see with fresh clean coolant in system and new cap and I am neither boiling or overflowing the reservoir. Granted bhgs are common on this car but it doesn't mean that's the first thing you tell people to replace. Sometimes its the stupid little things.
 

Roger UK

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Nobody is telling you to replace your Head Gasket . . . yet ! Not until you've done proper tests.

It's just that I doubt very much if your problem is down to the Rad Cap.

Some of us have had a lot of experience of these 7M engines . . . myself it's 15 years . . . and we know all the regular symptoms and what does and doesn't cause them.

If you've only driven a couple of hundred miles since replacing your rad cap, you can't possibly tell whether your symptoms have gone away.

People kid themselves that because it didn't pressurize the next day, that the engine must be OK. (and whatever they changed has fixed it). But when these HGs start leaking, it will often pressurize only every thousand miles or more . . . but gradually start happening closer and closer together.

When it happens next time, probably in 3 or 4 weeks, I would seriously recommend getting a sniff test, to see if there are any exhaust gases in the coolant. Changing the HG before it gets too bad is the only way to save your big ends.
 

VET88M

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Quick update Cts was also bad so that's been replaced
No more boiling over or over flowing
So thats following replaced

Cts
Radiator cap
Radiator flush
 

VET88M

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F00g00 you are correct Cts is coolant temp sensor some people also refer to it as a ets. Cts is the sensor that the ecu reads on 7mge its located buy the thermostat housing under the gauge temp sensor. Gauge temp sensor will be one wire while the Cts is a two wire.
Cheap replace is a gm sensor but you need a gm pig tail. Or you can find oem one for 30-50$ online in most cases