Importance of Engine Operating Temperature

[bobojay]

Originally Posted by booster

Might be time to block off the radiator on that one!

Yep...think so too

[markopolo]

I'll take it out on the highway tomorrow to see if the temperature improves. I hadn't thought of it but blocking the radiator is an option as you two pointed out and apparently not that unusual with these diesels.

I have some troubleshooting steps to work through also. Thermostats and temperature sensors if necessary look to be fairly straightforward replacement items and not that expensive.

[markopolo]

I think one or both of the thermostats aren't working correctly (two in this van). The coolant temperature wasn't much better after mixed driving for an hour today. The hottest I saw was 150*F. Looks like we're about 1 week away from some cold temperatures so I'd like to replace the tstats this coming week.

The recommended tstat is rated 195*F. ACDelco offers 190*F, 195*F & 205*F to fit this engine.

My preference would be ACDelco & I'll make some calls Monday to see if any are nearby. The local NAPA should be able to get a Gates premium 195*F by Monday afternoon.

Any opinion of Gates parts in general and the premium line specifically?

[booster]

Originally Posted by markopolo

I think one or both of the thermostats aren't working correctly (two in this van). The coolant temperature wasn't much better after mixed driving for an hour today. The hottest I saw was 150*F. Looks like we're about 1 week away from some cold temperatures so I'd like to replace the tstats this coming week.

The recommended tstat is rated 195*F. ACDelco offers 190*F, 195*F & 205*F to fit this engine.

My preference would be ACDelco & I'll make some calls Monday to see if any are nearby. The local NAPA should be able to get a Gates premium 195*F by Monday afternoon.

.

Any opinion of Gates parts in general and the premium line specifically?

I can't speak specifically to Gates thermostats, but I gave up on aftermarket thermostats many years ago after too much trouble with them. Bad temp control, both from setpoint and swing variance. Substantially shorter life most of the time. something like 1-3 years instead of 5-10. Now I just bite the bullet and go to the dealer and get one.

It is interesting that Rock auto has a couple of brands including Gates and AC Delco, and the AC is nearly 4 time the cost, so something has to be different beside profit margin, or even country of origin, I would think. They list a few different ones, but they didn't say anything about 2 thermostats, though.

Have you felt the upper radiator hose to see how fast it gets hot? This can often be a good indicator of if the thermostat is stuck open or opens too soon, if the hose starts getting warm right away. You can tell pretty easily if the hose gets warm and is about the same temp as the thermostat housing when you are shortly after startup.

[markopolo]

I'll try that tomorrow.

From AC Delco:

Per Vehicle: 1; Years: 1996-1997

Per Vehicle: 2; Years: 1997-2002

99.99% sure mine fits into the 1997 to 2002 group for the tstat(s). It does for everything else I've looked at and/or worked on.

I don't think the Gates tstat from Napa was the right one.

[booster]

Originally Posted by markopolo

I'll try that tomorrow.

From AC Delco:

99.99% sure mine fits into the 1997 to 2002 group for the tstat(s). It does for everything else I've looked at and/or worked on.

I don't think the Gates tstat from Napa was the right one.

I suppose if they are the same thermostat, they wouldn't mention a different location, so maybe they are both the same.

[markopolo]

For this van, I see the two t-stats side by side when I look at the diagrams illustrating replacing the t-stat housing.

A Napa Canada search turns up the type of t-stat I need when I look at '98. '96 & '97 parts can get mixed up - I saw that with suspension parts.

The Napa Canada part number is the same as Gates and is rated 190*F which might be better for towing. My guess is that the Gates 33922, AC Delco 131-103 & Stant 14399 are the same. The product image on all three sites is the same right down to the scuff marks & flecks of dust. It will probably come down to what I can get on Monday. Two GM dealers are not far and the local Napa get parts by afternoon if ordered early enough.

It'll be interesting to see what difference this makes and I'll repeat the previous test or part of it if temps come up quickly to add more data to this topic.

[booster]

It sounds like they must have had some cooling issues with the earlier 6.5 liter diesels. Details and timing of the changes here:

Dual Thermostat Housing identification - Diesel Place : Chevrolet and GMC Diesel Truck Forums

When I looked at the thermostats, they had pix of the housing, but they looked to all be single, so must have been old pix. The link also mentions them having a high output water pump after the change, so that would be important to know if you ever have to change the pump, so you get the right one.

Thermostat housing at the rear of the engine, the link says, so this will likely require doghouse removal?

[markopolo]

I'm just figuring out that now ..... I see the instructions evolved in later model years to include doghouse removal. From the front I can only get a finger on two bolts. I don't see anyway to get a tool on them and there are 4 bolts anyway!

The upper hose didn't warm up that quickly. It did get to 108*F (infrared thermometer) after a while - probably 10 minutes or more. Coolant temp was 127*F before that.

I'll keep at it for a bit but if too much of a job I'll take it to a shop.

[booster]

Doghouse removable isn't too bad, at least on our later model, but I have always had at the seats out when I did it. Not sure if it can come out without moving them.

Your engine must sit a bit forward from ours, I don't think I can even see the rear of the engine from the under the hood.

[markopolo]

I might give up for a bit & do some more research. Lot's of things have to be removed to get to it from the rear. It would still be at arms length away though and there is a small diameter pipe blocking access to a lower bolt.

from rear d side.JPG

from rear p side.JPG

It seems to me the best way might be to remove the a/c compressor and get to it from the side.

from front next to compressor.JPG

I put it all back together inside and will replace the serpentine belt tomorrow while it is accessible.

[markopolo]

I just got some motivation. I got the service dept to look up the job specifics and it comes to 5 to 6 hrs in the shop. With tax and parts it could get to $800 here and I'm not exaggerating. 90% of the time involved is removing and later replacing everything that is in the way. I'll have the AC Delco t-stats tomorrow anyway so today I'll try to figure out what that pipe is that's in the way and blocking access to one of the four bolts. If I can move that pipe to get to that bolt then I can DIY.

[booster]

Yikes! 5-6 hours for a thermostat change is totally insane. That has to be right in the same area of absurdity as a lot of the heater core changes, only worse because it is considered a maintenance item.

Did he say if it you should go from the front or the rear? I looked in our 07 manual, but the 6.6L they listed had the thermostat in the front or the engine.

Good luck

[markopolo]

I didn't ask. I might have the same instructions he has. It is both front and rear access I'd say. Rear access with long extensions to start loosening and finish tightening the bolts (mainly for the lower two bolts). Front access to be able to actually reach/touch the cover and the t-stats to remove & replace and then finger tighten the cover bolts.

[booster]

I will certainly bet that cleaning the gaskets surfaces on the housing will be a tough reach.

[markopolo]

It'll be by feel mostly. The instructions for most years seem like it is doable from the front. One year has the 13 step removal & 13 step installation.

[booster]

Would it be easier to just remove the entire housing from the heads? The pix I saw seemed to show those bolts straight out the rear, assuming the housing could come out the rear.

[markopolo]

I'll plan ahead for something like that & get the two gaskets for that crossover housing. The air conditioner compressor blocks access to two bolts on the crossover housing so I can't do it that way but the shop could.

I think I'll phone the service dept again and see what removing & reinstalling the crossover housing would cost. If they approach it that way it should be much less.

I did spend some time on it today. There's a steel pipe - I think fuel related - that blocks access to the two lower bolts on the thermostat cover. It runs across both bolts just below their midpoint. Previously I thought it only blocked one bolt.

I put a new the serpentine belt on & put everything back together.

[markopolo]

I read more stuff on this last night. GM indicates this engine should get up to operating temperature in 7 minutes. I did a 7 minute test this morning. Radiator top hose measured with infrared thermometer and Scangauge both indicated around 51*F at startup (van in garage overnight). Ambient temp outside was 34*F. There was very little change in the top hose temperature after 5 minutes and the Scangauge indicated something like 98*F and the dash gauge hadn't moved. At 7 minutes the top hose got to 58*F and Scangauge was showing 122*F. The dash gauge had just moved a notch which I think would indicate around 165*F.

Based on that, I don't think either thermostat is stuck open. It seems more like one or both are opening early. Next test will be blocking the grill to see what effect that has.

Operating temperature is listed at 190*F which I think is a bit cooler than the gas engines.

[booster]

It certainly looks on the cold side, and slow. When the thermostats go bad, it is usually because they don't close all the way, which moves the whole curve slower and colder. You get the symptoms like you are seeing, for the most part.

On one of the thermostat discussions I saw when looking at the thermostats mentioned to use only the AC Delco thermostats, especially in the high flow waterpump models like you have. Apparently the pump has so much pressure and flow, it can overpower the thermostat and force water through them.

I think that in the thermostat world, 190-195* are the same rating, as the ones I have tested in a water on the hotplate varied way more than that . 90* C is 194F, so I think many are based on that.

I there is room for it, when you block the radiator, I usually use two pieces of cardboard, right against the radiator. Both can be the same size and cover 1/2, plus an inch, over the width of the radiator. That way you have continuously adjustable coverage from total to just over 1/2 of the radiator.