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View Full Version : How do you get the thermostat to open?


nick
12-14-2010, 09:42 AM
I've tested my brand new, 189 degrees F thermostat in hot water. It opens perfectly.

I install it in my 83 d24t, and I just can't get the thing to open. Both ends of my head will be around 210 degrees F, while the thermostat housing is only at 140 degrees F. The top portion of my radiator is 175 degrees, while the lower portion and lower hose are not even 100 degrees. I've spent over 10 hrs trying to bleed air out of the system and get the water to flow.

I'm driving around with no thermostat since I can't seem to get mine to open. I even tried drilling a couple holes in a different working thermostat and installed the thermostat orienting the holes towards the top of the bore for water/air to flow. It still won't open.

I've never experienced so much trouble with a thermostat on any vehicle. Any advice?

Volvoist
12-14-2010, 10:26 AM
Where are you bleeding the air from? Sounds like something is wrong. Could be a defective water pump or you have a lot of air somewhere. I've never (knock on wood) had trouble beeding a D24/D24T.
Does it overheat or just run hot? Since the thermostat sits in the block, that side should get hot first, thus opening at the correct temperature. Also, make sure that it is installed properly. The longer end (with the spring, etc.) goes into the block.

nick
12-20-2010, 04:06 AM
It is running hot, but not overheating. The thermostat will only fit one way: the long portion into the block.

The blades of the water pump look great. The bearing is tight too. I don't see how it might not be pumping the water properly.

I've been bleeding the air from the top of the cold start device. In latter attempts in get everything working properly I've been bleeding air from the thermostat housing hose.

95% of my radiator and 100% of the lower radiator hose is still stone cold while the head is 210 deg F.

Volvoist
12-20-2010, 05:39 AM
Silly question, have you checked your radiator? Could be poor circulation through it. Also, without a thermostat in it, does it warm up at all? Could be a bad head gasket causing air pockets, though it would build up a lot of pressure in the system nearly immediately after starting it.

ngoma
12-20-2010, 10:40 AM
95% of my radiator and 100% of the lower radiator hose is still stone cold while the head is 210 deg F.
That does sound like radiator blockage.
What is the cooling system history prior to this incident? What led you to change the tstat? Was this happening w/ the old tstat?

casioqv
12-20-2010, 03:47 PM
If you tested the thermostat in water and it's opening fully at the correct temp, than your problem is almost certainly something else (possibly the head gasket, or water pump from your symptoms).

What temperatures is your engine reaching, and under what conditions? How are you measuring it?

v8volvo
12-20-2010, 11:09 PM
I've been around and around on the cooling systems on these engines, trying to make them run at the right temp. My '83 764 TD (same year and setup as yours) runs hot on hills, and even just around town if I hammer it from stop light to stop light I can see the gauge walk up from 9:00 to 10:00. I've put thermostats in it; I've replaced the water pump; I've checked and rechecked the headgasket (which I know is new on yours anyway), I've fooled around with cam and pump timing; I've tried restricting flow in the the hoses to the oil cooler, heater and cold start thermostat in an effort to force more flow through the rad... all of that has had no effect. I believe a plugged radiator is probably the only thing left that it could be.

The only D24T I have owned so far that really has zero cooling issues is my '85 745 that I put a different motor in over the summer. It's a good motor with a good head gasket, and I installed a good (aka non-GMB-style with big impeller) water pump in it, along with a brand new Nissens radiator and a new OEM Volvo thermostat. The thermostat was in a Volvo box but it said Wahler on it and looked identical to the Wahler t-stat I can get through IMC for the D24/T, so as far as I can tell it is exactly the same... BUT, the car with the thermostat that came out of the Volvo box never budges the gauge even if I leave my foot pressed to the floor for a solid five minutes straight climbing Rainy Pass, whereas the 764 with the t-stat out of the Wahler box quickly creeps up to the red if I do the same thing. The difference could only be either the thermostat, or the radiator, which is new in the wagon and older/suspect in the sedan. But the key point to this story is that the only car that I have been confident is really, truly trouble-free is the one where I pretty much just replaced EVERYTHING in the entire cooling system. That made it happy. I think these cars have a fairly narrow margin of cooling capacity, where it has just enough to keep it cool even in extreme conditions if everything is working perfectly, but as soon as one component starts to get compromised you can start to see cooling issues come up. They just don't seem to be tolerant of much neglect in that area.

ALSO, though, the temp gauge logic changed in the '84+ cars. The '83s had a non-compensated temperature gauge circuits, while after '84 it used a compensator. In essence, that means that the gauge on an '83 760 is telling you exactly what the sender in the motor sees, while the gauge in the '85 is giving me an approximation that may be ironing out small fluctuations in temp, etc. Essentially the compensated gauge in the '85 makes me believe that the engine gets up to temp faster and stays more stable, while the '83 makes me worry more but maybe is the one that's telling me the real truth.

Any engine will fluctuate somewhat in temp as load and ambient conditions vary, and most modern cars have some degree of damping or compensation in the temp gauge circuit to keep nervous drivers from freaking out when they observe normal temp variation on the gauge. In fact that's part of the big disaster that Ford is dealing with on the 6.0L Powerstroke engines, which have cooling system issues that can cause a sudden overheat... but they put too much damping into the gauge, so if the engine overheats fast enough, it can actually get hot enough to damage itself before the gauge even registers and alerts the driver to what's going on so he can pull off an do something about it. :rolleyes: In any case, on the '83 D24T, it should be pretty steady and the head should probably not be getting that hot, so you may have a blocked rad or air pocket or other impediment to proper flow... but just because you see a little bit of normal movement on the gauge when driving wouldn't necessarily make me think there was a major problem, as long as it never moved too high or too dramatically.

TheShadow
12-21-2010, 04:58 AM
Very educating post. Thanks a lot!
Having a D24 NA with a very nervous temp gauge (a steeper hill, a bit more pedal, etc... makes it go a bit up, sometimes a few milimeters from the red part) makes me think that I need to do something about the whole cooling system...

Regards

Volvoist
12-21-2010, 05:31 AM
Also, I have ran into faulty temperature senders that seem way over sensitive on them. Seemed to be mainly in the late 83-late 84 model years. After putting a gauge on each suspected motor, I have always come back to replace the sensor. May also be worth looking into.

casioqv
12-21-2010, 10:25 AM
I think most D24s could benefit from a $65 tropical fan clutch from FCP (http://www.fcpgroton.com/product-exec/product_id/2345/nm/Volvo+740+Turbo+Fan+Clutch+Tropical+1985-1991+(Aisin)), a brand new radiator, and Zerex G-05 coolant which will keep the radiator from plugging up again. Also, a totally separate digital temperature gauge of some sort. The factory temp gauge is total crap IMO, even in the 83/84.

heavyequipment
12-28-2010, 04:54 PM
I use an infrared thermometer for checking temps in different parts of the engine. They're not hard to find these days. This engine is the only one I've ever seen that circulates the coolant "backwards", i.e. the water comes out the top and returns through the thermostat at the bottom. I wonder why they did that... The system should bleed itself by letting air out of the top of the radiator into the top of the surge tank. You just have to fill it up and then recheck it after running several times.

Regards,
Chuck Yarter

nick
12-29-2010, 07:41 AM
I've been using an infrared thermometer to check the temps of the head and thermostat housing. I replaced the blown head gasket over Thanksgiving break. Thanks for the information v8volvo, its great to know I'm not alone with these issues.

I think that the culprit is most likely the radiator. The previous owner said that he had it rebuilt by a shop near him. I will begin searching junkyards for a replacement radiator since a new one is approximately $300.

nick
01-17-2011, 03:38 PM
I decided to try a 170 degree thermostat. Now it works perfectly! Praise the Lord.

heavyequipment
03-24-2011, 07:45 PM
The volvos I'm familiar with (most all through '88) have a buffer circuit in the instrument panel that keeps the temp gauge from actually following the temperature as long as it's in the normal range. Seems some drivers get nervous if they see the needle move too fast. IPD sells a replacement for the (plug-in) card that makes the gauge follow the actual temperature. The same thing can be achieved by soldering a jumper wire on the buffer card.

This may account for different operation of temp gages on different cars, if someone has wired out the buffer.

The D24 cooling system is different from any I have seen before, and I've been a professional mechanic for 50 years, on both diesel and gas equipment. The coolant enters the engine through the thermostat and leaves through the upper hose. Still, I haven't noticed any issues in the way it works (till it blew the bottom hose and cracked the head before I noticed overheating).

Nevadan
08-06-2013, 01:22 PM
The volvos I'm familiar with (most all through '88) have a buffer circuit in the instrument panel that keeps the temp gauge from actually following the temperature as long as it's in the normal range. Seems some drivers get nervous if they see the needle move too fast. IPD sells a replacement for the (plug-in) card that makes the gauge follow the actual temperature. The same thing can be achieved by soldering a jumper wire on the buffer card.

This may account for different operation of temp gages on different cars, if someone has wired out the buffer.


I'm interested in having my temperature gauge accurately reflect the actual engine temperature. After reading the above post it sounds like this is the fix.

So, how do you jumper the buffer card?

Or, what is a part number for the IPD replacement card? (I couldn't find it on the IPD site.)

ngoma
08-06-2013, 09:58 PM
So, how do you jumper the buffer card?

Or, what is a part number for the IPD replacement card? (I couldn't find it on the IPD site.)

That buffer card is in the 240 series instrument cluster. If something similar exists in the 7xx/9xx series, it is embedded deep inside the cluster circuitry.

Personal experience: Swapping instrument panels from different 740 TDs gave different temp gauge behavior. Some stayed near halfway point after warmup, others varied more when climbing hills for example. Same engine, same car, so there is some variation in gauge reaction.

IMHO, for serious temp. monitoring, get an aftermarket sensor/gauge, preferably digital. Factory equipment can be notoriously inaccurate, most likely to avoid complaints from the new purchaser of the vehicle.

The temp gauge sensor is at the front left side of the head, near the #1 GP.

Nevadan
08-07-2013, 06:34 AM
The great thing about this forum is when you ask the right question you get an answer from someone who has experience. I value that experience!! Is there a way to donate to the forum?

I'll get an aftermarket gauge. I already rebuilt the entire engine bay wiring harness so I know the wiring is sound. I might replace the sensor just to test it.

745 TurboGreasel
08-07-2013, 01:49 PM
Here is the story when i walked this trail.
http://forums.turbobricks.com/showthread.php?t=141850

I have a big dead spot from 175-220ish.

Nevadan
08-08-2013, 08:10 AM
Thanks for the link. There's a lot of useful data there, not just opinions but actual facts.

MoeTell
08-14-2013, 01:03 AM
Does it get too hot or just run hot? Since the heat range rests in the prevent, that part should get hot first, thus starting at the appropriate heat range.

745 TurboGreasel
08-14-2013, 12:24 PM
I will gradually overheat if I cruise over 90MPH, or less if uphill.