1998 v70 overheating, coolant circulation problem

mikesail · Post by **mikesail** » 22 Oct 2009, 19:50

Hi, just signed on after lurking for a few years. Very well run site I must say, the fix for my 816 radio was very helpful.

My v70 GLT had its motor replaced two years ago after a meltdown caused by a failed radiator. By the time the CE light started blinking it was too late, lost compression and pretty bad noises. Car had 150k at this time. A shop installed a used motor for me, it was a later model that they put the old 98 distributor on to make it compatible. It runs well, but was always very hot according to the OBD port read by a scan-gauge. After about nine months, the head warped and the shop reworked it under warranty. The car runs well again, but still was hot, no longer have the scan-gauge to check though.

I first had some episodes of overheating this summer on a hot slow freeway drive in So-Cal. After the heat wave ended it did not overheat but then started using coolant at a regular rate. I believe that the coolant was being lost through a leaky cap. I replaced the cap which slowed the coolant loss. Later I replaced the thermostat, though it appeared to still open ok when put in boiling water. When replacing the thermostat I ran a garden hose into the top of the radiator to check that it flowed freely out the thermostat housing, thus proving the rad and block are clear.

The car will now overheat on a warm day. When I pulled over with the gauge near the red, observed that the fan was blowing rather cool air and the lower hose was not very hot at all. The upper hose and block were quite hot, able to boil water on the thermostat housing. The lower radiator hose seems to be fine, I don't think it was collapsing.

My next test was to run the engine with the thermostat housing open, and a garden hose into the radiator top. As before water will run freely through the block, but revving the engine caused no visible flow increase out of the thermostat housing. It appears to me that the water pump is not causing any circulation.

I have now removed the water pump, and found it to be intact. Somehow I am missing something fundamental here, why do I not see a vigorous output from the pump? Is there something unusual about the coolant circulation in this engine?

I appreciate any help, thanks Mike

Post by **Ozark Lee** » 22 Oct 2009, 20:48

Welcome to MVS Mike,

You have a very good description of your diagnostic work and you almost leave me without questions to ask.

When you say "very hot" on the scan gauge what is the actual temperature?

When you replaced the cap I assume that you put on a Greenish Blue cap rather than the gray cap. The gray ones are real trouble since they split and won't hold pressure. The boiling point of the coolant is proportional to the pressure in the cooling system so it will start to boil out at a much lower temp without the cap holding pressure.

PV=nRt - Google Ideal Gas Law for details.

You may have a bad ECT sensor that isn't telling the ECU to turn on the radiator cooling fan on or it could be a bad cooling fan relay. The latter is a common occurrence.

Kick on your air conditioner and see if the engine cooling kicks on within a few seconds of the A/C compressor - if not focus on the cooling fan relay.

...Lee

Post by **JDS60R** » 22 Oct 2009, 21:18

You were right to suspect the cap and thermostat as well as the pump. Flow in the block is controlled by 3 things (internal restriction, pump output and thermostat restriction)
You ruled out internal restriction with the hose
You ruled out pump issues by pulling the pump.
The thermostat is left - its bad
replace it ASAP and hope for the best as these motors loose the head gasket quickly .
Also - Volvo has moved to suggesting the replacement of the thermostat housing and thermostat on newer models (not sure why but they do -perhaps it warps with heat and effects the next thermostat).

I would replace both with an OEM in this case ( Bought through a discount vendor) .

This should restore flow and should resolve the cooling issue. If your radiator isn't getting hot then all of the heat is staying in the motor (bad)

Let us know how it works out.

mikesail · Post by **mikesail** » 22 Oct 2009, 23:07

Ozark Lee wrote:Welcome to MVS Mike,

You have a very good description of your diagnostic work and you almost leave me without questions to ask.

When you say "very hot" on the scan gauge what is the actual temperature?

usually over 200. up to 230 on hot days. The gauge doesn't move until 241 and red zone is about 247.

When you replaced the cap I assume that you put on a Greenish Blue cap rather than the gray cap. The gray ones are real trouble since they split and won't hold pressure. The boiling point of the coolant is proportional to the pressure in the cooling system so it will start to boil out at a much lower temp without the cap holding pressure.

PV=nRt - Google Ideal Gas Law for details.

BSEE UCLA 1984

You may have a bad ECT sensor that isn't telling the ECU to turn on the radiator cooling fan on or it could be a bad cooling fan relay. The latter is a common occurrence.

Kick on your air conditioner and see if the engine cooling kicks on within a few seconds of the A/C compressor - if not focus on the cooling fan relay.

ECT sensor should be fine as the OBD port read a believable value in the past when I had scan-gauge. Fan is running fast when overheating. Relay operates correctly when each coil is grounded. AC is not working at this time.

...Lee

I still am focused on not seeing water gushing out of thermostat housing when running the motor, any thoughts?

mikesail · Post by **mikesail** » 22 Oct 2009, 23:12

JDS60R wrote:You were right to suspect the cap and thermostat as well as the pump. Flow in the block is controlled by 3 things (internal restriction, pump output and thermostat restriction)
You ruled out internal restriction with the hose
You ruled out pump issues by pulling the pump.
The thermostat is left - its bad
replace it ASAP and hope for the best as these motors loose the head gasket quickly .
Also - Volvo has moved to suggesting the replacement of the thermostat housing and thermostat on newer models (not sure why but they do -perhaps it warps with heat and effects the next thermostat).

I would replace both with an OEM in this case ( Bought through a discount vendor) .

This should restore flow and should resolve the cooling issue. If your radiator isn't getting hot then all of the heat is staying in the motor (bad)

Let us know how it works out.

I agree about the head gasket, you'll see I already had that happen!
Thermostat was replaced, even though the old one seemed to be ok.

9394volvo850s · Post by **9394volvo850s** » 22 Oct 2009, 23:17

mikesail wrote:
Ozark Lee wrote:Welcome to MVS Mike,

You have a very good description of your diagnostic work and you almost leave me without questions to ask.

When you say "very hot" on the scan gauge what is the actual temperature?

usually over 200. up to 230 on hot days. The gauge doesn't move until 241 and red zone is about 247.

When you replaced the cap I assume that you put on a Greenish Blue cap rather than the gray cap. The gray ones are real trouble since they split and won't hold pressure. The boiling point of the coolant is proportional to the pressure in the cooling system so it will start to boil out at a much lower temp without the cap holding pressure.

PV=nRt - Google Ideal Gas Law for details.

BSEE UCLA 1984

You may have a bad ECT sensor that isn't telling the ECU to turn on the radiator cooling fan on or it could be a bad cooling fan relay. The latter is a common occurrence.

Kick on your air conditioner and see if the engine cooling kicks on within a few seconds of the A/C compressor - if not focus on the cooling fan relay.

ECT sensor should be fine as the OBD port read a believable value in the past when I had scan-gauge. Fan is running fast when overheating. Relay operates correctly when each coil is grounded. AC is not working at this time.

...Lee
I still am focused on not seeing water gushing out of thermostat housing when running the motor, any thoughts?

since you have the waterpump out try putting the hose in there see if it comes out the other side.

mikesail · Post by **mikesail** » 23 Oct 2009, 10:41

I still am focused on not seeing water gushing out of thermostat housing when running the motor, any thoughts?[/quote]
since you have the waterpump out try putting the hose in there see if it comes out the other side.[/quote]

Water flows freely through the block and radiator with the garden hose.

Post by **JDS60R** » 23 Oct 2009, 11:36

remove the thermostat housing - you must take the thermostat out of the equation to see if the restriction is internal or the thermostat.

I am betting its the thermostat - yes I understand it was replaced but th averages are on the thermostat currently installed as being the restriction.

Remove the thermostat and check for flow - do not do this while the car is running the cold water against the hot block will cause a strong thermal variance and crack the block/head and lift the gasket.

Post by **confused_al** » 23 Oct 2009, 11:38

Check the bleeder valve of the thermostat, make sure it is positioned to the front.

mikesail · Post by **mikesail** » 23 Oct 2009, 15:50

confused_al wrote:Check the bleeder valve of the thermostat, make sure it is positioned to the front.

hard to understand how this could matter, can you explain?

I verified that the thermostat opens at the correct temp with my stove.Both the main valve and bypass circuit move correctly.