Gradually overheats UNLESS Revved

[Aliens]

Has anyone had this before etc and would know the probable cause.

Basically the engine "doesn't stop warming up".

Once it has warmed up to roughly the half way mark (maybe after 30 mins from first start), the temp will DROP FAST IF ENGINE IS REVVED.

After more time has passed, the temp will eventually get to the full-hot mark. However, revving the engine (e.g. taking off) will still cool it down - just not as much.



1.) Coolant/water ratio is about 3/4 coolant or better.

2.) Coolant is 100% full.

3,) Coolant level has NEVER gone down, ever.

4.) Coolant NEVER has "boiled" - even after having reached full hot mark.

5.) Coolant has NO leaks anywhere.

6.) I believe that the thermostat works, because BOTH of the MAIN radiator hoses become STIFF (with a little tiny amount of "give") once warmed up.

7.) Oil quality and level etc is excellent.

8.) ZERO mixing between Oil & Coolant.

EDIT: 9.) Thermo Fan always works properly.

 

[levymetal]

v6 or v8? if it's v6, does the thermo fan turn on? v8 - maybe clutch fan is busted. i believe it should be easy-ish to turn by hand when cold, harder to turn when hot. engine off of course...

and by revving, do you actually mean sitting there stopped and revving? reason i ask is because you described 'taking off' as revving - if your car starts moving, then you get air flow through the radiator, thus cooling down.

 

[Aliens]

I used "taking off" as an example; Actually revving the engine (even while stopped) always cools the engine down quite well (according to the temp gauge).

I had to do this today while sitting at the last few traffic lights (revving it without moving e.g. with the foot on brake to keep the engine cooler).

I forgot to mention about the fan. It does always work properly.

v6 or v8? if it's v6, does the thermo fan turn on? v8 - maybe clutch fan is busted. i believe it should be easy-ish to turn by hand when cold, harder to turn when hot. engine off of course...

and by revving, do you actually mean sitting there stopped and revving? reason i ask is because you described 'taking off' as revving - if your car starts moving, then you get air flow through the radiator, thus cooling down.

 

[greenfoam]

Should have air in there somewhere, that's what happens when they get air in them

 

[vlv8vic]

tend to agree with air and although i don't think it's a head problem this is exactly what my old car did when the head went, even though there appears not to be oil mixed with water or vice-versa. It took a number of weeks of sitting to show a small contamination.

 

[Morton]

Yeah, take off the rad cap and give the hoses some squeezing while it's running and the heater is on

 

[Garth]

correct me if im wrong, but dont the v series have a little bleader at the top of the thermistate housing, ? depending on the series ofcourse, im sure my dirty vn (s2) had a bleader valve ontop.

 

[Morton]

A 1988 won't. It's series 1 before any revisions, with the thermostat at the back.

 

[Aliens]

Well I've had a few of these 88 and earlier 89 engines, plus a couple of series 2 ones, all of which I've let major amounts of air in/out of the coolant system (e.g. changed an engine and/or radiator). I always do the same thing - let it run until the thermo opens with the S1 botle cap off, then fill with coolant and squeeze hoses until no more air comes out, and the coolant system seems full. Then replace cap, let cool, then re-check...

I've never had this problem before - even on two others I've had to do at least some head/manifold gasket replacements on.

The closest I got was on a S2, where there was a leak in the lower radiator hose, hidden under its hose clamp.

But this caused overheating - where it got WORSE when the engine was revved.

In the case I'm asking about, the overheating is more gradual, and gets BETTER when the engine is revved.

Was thinking about just chucking in a bottle of Chemi-Weld. I read lots about this a while ago and that plus my experience with virtually all other stop-leak type products, makes me think that one bottle of chem-weld might just work magic.

Although the coolant level is STILL 100% lapping at the top of the coolant bottle, making me think there's no use trying to plug a tiny leak that doesn't seem to exist.



As another note... How hot could the coolant actually get? As mentioned before, I've never witnessed it boil (I guess because it's almost 100% coolant). Hot enough to blow anything? The caps I like to use are the Repco ones with "135psi" labelled ontop.

 

[Aliens]

Just an update. With that car I discovered that I actually didn't really bleed the cooling system after I had the right hand head block off the motor one Sunday.

When I thought back, I remembered that I didn't have time to bleed it properly, and thought "I'll bleed it properly later" and filled it up then put the coolant bottle cap back on.

Of course, I forgot to bleed it.

However, this particular motor still gets warmer than normal. All Series 1s I've had, with properly operating cooling systems, have generally had the temp gauge needle sitting on or around Notch-1. This one gets to about 3/4 in worst case situations, so far.

Alway, Chem-i-weld can't work in a Series 1, because of the fact filling is through a bottle rather than the radiator.

The product just clogs the outlet at the bottom of the container.