T stat "valve closed", not only circulation problem but also may create the air pocket. Without a T stat you should get even heat and easier coolant fill BUT it takes longer to warm up especially in colder weather. I have run Volvos without Tstats in mild Oregon winter for the whole season. In hotter climate tropical countries drivers take the T stats out for good--all they do really is provide quicker engine heat and they don't need heaters there at all. With modern cars though, lack of T stat may cause running issues and check engine light to come on.

 

btw, on a 740, you need vacuum to open the heater valve, on a 240 its cable operated. there's normally sufficient vacuum in a 'storage bottle' attached to the HVAC stuff to open and close everything a few times after shutting the engine off, you can test this by parking the car in a quiet place, shutting off the engine, then listening carefully while you cycle the air vent mode **** several times to different positions, you should hear faint whoosh/flap sounds as the air flaps open and close, but after doing this several times, it will fade out and stop working til you run the engine again and recharge the vacuum. if you do NOT hear this sounds, the one-way valve between the intake manifold and the HVAC subsystem is likely leaky, or the vacuum bottle thats tucked down inside the firewall is leaking (it looks like a black plastic egg carton).

anyways, if you turn the heater control to full heat before you shut off the car, there should be sufficient residual vacuum to keep that heater valve open indeinitely if there are no leaks in the system. or worse case, you can manually prop the lever at the valve open, using a bit of bailing wire or something.

 

Hey guys

So that new T stat from AutoZone was not OEM after all, and didn't seem to be fitting right. Was also getting no heat at upper hose while very hot at lower hose, didn't know if that's what's supposed to happen. So I took it out. With all the coolant that's gotten dumped with all the T stat removal and replacement and re-removal I've practically swapped out all the old coolant, but it's still turning up filthy in the reservoir after all the requisite burping, so full flush coming this weekend.

Unfortunately I am afraid that I may have put a little too much elbow grease into scouring the surface on the engine block where upper rad house couples with block and now it seems I can't get a good seal there? Is there a gasket that could remedy this?





Meanwhile, temp gauge still not responding even when I am sure (from the even and substantial heat coming from lower and upper rad hoses) that I am at operating temp. Also am noticing that when I start up the car right away finds "target RPM" of 600 and stays there, but if I give it even a little throttle when idle comes down it settles and stays at 1500 RPM. This is consistent at the moment (with thermostat out). I am also noticing that when RPM is 600, heater blows tepid, but at 1500 RPM it feels like an actual working heater. (Don't think it's an air pocket causing this? I'm no burp-master but after a day of this I think I'm getting a feel for when there's no more air hiding down there...)

Also noticing that it seems much harder to slide temp selection lever from cold to hot than it is to slide from hot to cold, is this normal? (I do have good vacuum according to pierce's "whoosh/hiss" test when manipulating air mode lever.)

I'm sure I'll have more questions come flush-time. Thanks for your patience.

 

my 740 had the newer style rotary temp ****, it turned very smoothly and evenly in both directions.

 

Did you ever deal with the Coolant Temp. Sensor? That may affect the idle speed at start up. Does the idle speed settle at 1,500 once warmed up?
The heater working better with higher RPM--core could be partially obstructed, the increased flow with higher RPM moves higher volume of liquid. Is the heater valve open al the way?
I forget what year this car is, but you have the slider type controls and they get sticky--they operate cables and I am sure those are tired and rusty. You can try lubing as much as possible but not that much is easy to get to....

 

Hey

It's a 1990 740 GL. The cold/hot slider (which appears to manipulate vacuum as opposed to cable?) got easier to move with exercise and over the course of flushing. Which was very satisfying as there was a lot of filth (I'm actually going to give it a third flush tomorrow bc i'm not yet fully satisfied!). I'm not sure if moving the lever all the way to right (to hot) is in fact opening the valve all the way but I hope it is... I do in fact have good vacuum, as per pierce's "whoosh/hiss" test...

Re: 1500 rpm idle. The pattern is that when I start up it settles at 600, but the moment I touch throttle (as I have been doing to get that washing action going), let's say revving to 3000 rpm, it settles to 1500 rpm and always settles there after every subsequent rev. I still don't know how to test coolant temp sensor but at this point (lots of gunk out, still no budge of the needle, even when I am sure from heat of hoses that I am at operating temp) I'm not sure what else could be responsible for my lifeless gauge...

Re: my thermostat struggles... any comment on whether my lower hose getting much hotter than my lower hose after I installed (non-OEM) thermostat was due to incorrect installation (or a crappy thermostat)? Do I need to be worried about that leak pictured above (it doesn't actually drip much and seems to drip less when car is running), and if so is there a gasket (or anything else) that would remedy it?

 

look at the heater valve, you can see it has a sort of vacuum bellow cylinder on the side, there's a pushrod coming out of this, thats connected to the lever that works the actual ball valve thats inline with heater water fittings.... when you move that lever from cold to hot, that lever should move from its cold/off position, maybe 60 degrees to the full hot/on position.

here's the original style heater valve....


and this is the current Volvo OE replacement part (note more plastic, less stuff to rust)



and I previously linked a much cheaper perfectly functional 'generic' heater valve that works just fine, but has no visible external lever.

 

Hey pierce. I see the vacuum hose connections on both my old (metal, visible-lever) valve and on the generic valve with no visible lever which I ended up buying at AutoZone. But how do you judge the function of the valve, i.e., the correlation of valve opening to cold/hot slider position, without a visible external lever on the valve? I'm pretty sure the valve is working (i'm feeling the vacuum creating resistance on the slider, and the slider changes the air from cold to hot... but how do i tell whether the generic valve is as open as it can get when the slider is all the way over to the right (maximum heat)?

Also... is it possible/advisable to fire water from my garden hose directly into the little hoses leading to the heater core in order to more "aggressively" flush it, much as when I fired water directly into the actual radiator, which seemed to get good results?...

 

yeah, the generic valve is all internal, so you can't see any actuator, but they are pretty damn reliable and unlikely not to work

the ultimate test would be heat, no heat while driving with the fan on medium...
and yeah, you can flush the heater core directly, as long as the outlet isn't blocked, hose pressure is unlikely to burst the core.

 

To do an effective core flush, it has to be reverse flushed, so direct the stream into the OUTLET, water comes out of the INLET. Also, what I do is to fill the core first with vinegar and let it sit for a time, to dissolve mineral deposits inside which is what mainly blocks the flow.
You can get an idea of flow to the core by feeling the temperature of the IN and OUT heater hoses. The valves are all pretty simple devices, generic or OEM, little difference--the vacuum operates a flap which opens and closes the flow. You can test it quite easily with little suction...
The thermostat as well is really simple and as long as it fits well it should work fine... No need for a pricey OEM one.

 

mercedes specifies a 100g citric acid per 1L water for lime deposit problem, you flush the system with water, fill it with this mix, run the engine on elevated idle for 15 minutes ensuring good coolant circulation, then flush it out and refull with coolant. they also have an alkali flush formula for oil contamination, like after fixing a head gasket.

 

Hey guys

Long day, including some first-time soldering on the fuel pump (looks like those dings on the locking ring and those electrical sleeve fragments at the bottom of the tank were from someone replacing the pump motor at some point and then doing a sh*tty job wiring it in, to say nothing of cleaning up), but finally finished my third and fourth flushes. I think I'm satisfied.





Some weird data (or at least weird to me) coming out of this adventure:

1) During the third flush, the idle hung just under 1000 rpms, and after each "washing rev" of the engine would settle back down to that RPM consistently, but despite the >1500 rpm idle this was the flush where I got the heater to feel like an actual heater. I think squeezing/massaging the OUT hose from the heater core, approximating a reverse flush maybe, helped somewhat; couldn't budge those hoses (though they both got quite hot for this flush), so no vinegar soak/direct reverse flush there yet, though I look forward to it;

2) During the fourth flush, the idle returned to its settle-to-1500 post-washing-rev pattern, but despite the higher idle the heater seemed to blow LESS hot this time around? (The upper and lower rad hoses didn't seem to get that hot either?) Might this have been due to the greater cleanliness of the system? Fairly certain there were no air pockets, I think I've learned the signs of a full-to-the-top system by now...

Filling with coolant tomorrow (unless you guys would recommend I keep flushing?). Going to take it on a drive to my Volvo guy soon to put some new brakes on the old beauty (hence it will be a fairly slow drive). Guess I'll see if I can get the heater to give me more love on that adventure? (Think I'm gonna run with no T stat for the moment, particularly since I got the heater to behave OK without it, however briefly; I'm OCD enough about getting a perfect fit with the T stat to wait on an OEM part from my guy in Atlanta, not to mention that I think I'm going to be ordering a new coolant temp sensor from him too, as my temp gauge is still showing no signs of life...)

 

I wouldn't flush anymore, you never get real clear water coming out...
Without a Tstat you'll get very slow warm up to normal temp, run too cold an operating temperature which is not good especially in cold climate. Good that you plan on installing the Tstat eventually.
I wonder why you are not getting consistent heat, something may be obstructing the flow. I'd still do the vinegar treatment to the heater core eventually.
Why don't you do the brakes yourself?

 

RE: brakes, hm.... is it really simply a matter of having the parts (and can you do them one wheel at a time while jacked up)? Is the installation that straightforward? Seems like there are a whole bunch of things you'd need to know/be able to detect in order to do this right? I mean, I'm hooked on the DIY thing by now, but I don't know if I'd stake my life on my abilities at this point...

That aftermarket T stat didn't even come with a gasket, and when I tried to put the old gasket on the new unit, it had to be worked into place in the coupler (as opposed to just dropping in, as the old one did), which probably explains why I struggled to get a good seal (which is why I started grooming, i.e., over-scouring, the facing surfaces)... so I think I really have to go OEM here.

I think I'm going to try the vinegar soak and reverse flush of the core today. Do you just pour vinegar into the OUT hole until it falls out? Would be very grateful for a step-by-step here too (or even just a tip or two on loading the core with vinegar)...

 

Brakes are much easier than what you have been doing! And they are pretty fool proof so it's hard to screw them up. What's wrong with them? Pads, rotors, calipers, all real easy bolt on stuff...
The core. You have to get the two heater hoses OFF the heater core at the fire wall, you said you had problems with them? Be careful not to break the pipe outlets or you will be looking at heater core replacement (no fun!). The hoses are hard to get off, many cut them to get them off but then you'll need new ones, hopefully yours are not that stuck... Once the hoses are off you have the In and Out pipes of the heater core expose. Plug one hole, fill up the core with vinegar as much as possible and let it sit in the core for a day, then reverse flush. The vinegar dissolves the deposits.
Autozone, OReillys and such are not good sources for Volvo parts. They have to do in a pinch but try to avoid them.

 

Hey

So the car threw a code, 2-2-1, "Oxygen sensor not operating," which the table says could be caused either by the oxygen sensor or an intake air leak. Maybe this explains my every-so-often 1500 rpm idle (which RPM it will sometime stop at after coming down from me giving it throttle, and to which will it sometime jump when I'm in park or neutral, which high idle makes shifting into drive or reverse a hard THUNK, after which shift idle will drop to 600 rpm). So I guess I need to figure this out before I turn to the core, which is apparently still clogged, still throwing tepid heat at 600 rpms even after reaching operating temp and only throwing real full-blast heat at 1500 rpms. (I'm wondering if my possible intake air leak is due to the stress I discovered I was putting on the vacuum hose connected to the top of the throttle body while I was struggling to get the old heater valve out.) Let alone the brakes, which sound like they will be a pleasure to work on compared to this sort of gremlin-chasing (my temp gauge is still completely dead btw...)

Any tips on dealing with this new issue?

 

An air leak should be easy enough to find, you have some clues...
O2 sensor usually causes no idle issues. Clear the code by disconnecting the battery for a couple of minutes, see if it reappears. O2 can be tested easily.
Yes, brakes are pretty straight forward but be careful sourcing parts as Volvo uses several different variants calipers and pads. I just did a 1995 940T, had four possible pads!

 

Disconnected battery and spread a glop of Gorilla Super Glue XL on the suspected vacuum leak before going to work this morning. Came back tonight, started up, drove around my driveway loop, and not only could not get the code to reappear but my idle never got stuck at 1500 rpm in park or in neutral or coming down from rev. So that felt good.

Treated IN hose with WD-40 last night (i.e., shoved wand between hose and firewall and sprayed, a lot). Tonight the hose was quite easily coaxed off. OUT hose felt very much like it needed same treatment so that’s cooking now.

A good night. Having another beer. Looking forward to tomorrow.

 

i can't tell, did you remove the clamp on that 2nd heater hose? I would plan on replacing those hoses, and any others you can, also using new clamps. its probably worth it to get the crimping tool for the correct crimped clamps and not using generic screw clamps, they often get under or over tightened, either is bad.

 

..."correct crimped clamps"? No, Volvo never used the crimped type on the Red Blocks, those came much later. The crimpers are just cheaper to make and one time use, that's why they are used now, they are by no means better!
I wouldn't replace the hoses unless they need to be replaced, unless you want to throw $ away... OEM parts are much better quality and much more expensive, if you can even get them today.