PontiacBonnevilleClub.com

Hey guys, new guy here. My name is Matt and I from queens NY
24 year old car enthusiast. Current owner of a 92 acura legend fully restored (jdm motor and tranny ,full bolt ons, custom suspension, custom ecu, 220 amp alternator and a 3,100 watt audio system).. 91 honda civic hatchback (currently being built for 12:1 compression and around 220 whp in a 2000 LB highly modified shell)..

I recently purchased a 91 bonneville to get me threw the winter.. I bought it as a winter beater but fell in love with it on the first ride. Currently having 2 problems that have me clueless.

1) car is getting 10 mpg!!!!
2) can't get a thermostat gasket that fits


Problem 1: average 10 mpg city and highway. Did plugs, wires, pcv, fuel filter, tranny and engine filters and fresh fluid, all motor mounts, o2 sensor and I reset ecu.

*** used seafoam threw vacuum house off brake booster. Smoke started coming out around the egr. Maybe I have a vacuum leak??****

Problem 2: I've used the felpro gasket and acdelco . Delco fits on edge of tstat and felpro sits on the center of the tstat. Both gaskets won't allow the housing to sit flush. I tried a 4 seasons housing and a new oem housing. All say 88-91 bonneville. Temp gauge goes down on highway speeds wit out the gasket. City driving is fine.


1991 bonneville ls
166k miles

New:
Ac delco plugs and wires
Pcv
Fuel filter
O2 sensor (walker)
Tranny fluid and engine oil change
Cleaned grounds and reset ecu
Sea foam threw vacuum and crank
Bottle of techtron in full tank of gas

On the thermostat - make sure the hole in the intake manifold is clean, and doesn't have remnants of the old thermostat housing in it. The bolts will not draw it in straight, you'll need to grease up the o-ring and work it on by hand, then tighten the bolts.

As for gas mileage, any service engine light on? Does it run smooth or is it misfiring?

If I remember correctly, you use just the rubber gasket around the thermostat itself, and not the paper gasket on that setup.

MattStrike wrote:On the thermostat - make sure the hole in the intake manifold is clean, and doesn't have remnants of the old thermostat housing in it. The bolts will not draw it in straight, you'll need to grease up the o-ring and work it on by hand, then tighten the bolts.

As for gas mileage, any service engine light on? Does it run smooth or is it misfiring?

Took it to a shop, they couldn't figure out the gasket issue either. I did clean it.. I put it in by hand and used a big flat head to keep it seated while I torqued it down (one bolt on the housing .. No bleeder valve??). It only fits with out the gasket. I was told I may need a new manifold if I want to fix it.. I was also told the temp gauge being at 140 is fine... First domestic car but.. Shouldn't these be at 180-195f for best performance and gas mileage?

No cel .. I see the cel illuminate when I turn the key so I know the bulbs good.
Runs great.. Very rarely will it shake on a cold RESTART (never shakes 1st start of the day)
I run only 89 octane in her too.. Was thinking about borrowing a fuel gauge to check the pressure.

Anything below 170 is too cold because that is when the engine goes closed loop (or open, I get them switched around sometimes). It's part of your fuel mileage problem most likely.

The thermostat and gasket should fit snugly in a ridge that is either on the top housing or the bottom, I cant remember, it's been so long.

I have 2 brand new housings .. 3 thermostats and a bunch of gaskets
Not one combo works. I have the above parts in both oem and aftermarket versions

Some pictures would really help for the thermostat housing issue. I agree that at 140 it's not getting up to temp and is going to hurt fuel economy. But 10mpg is really bad, you'd notice the engine is not running right I'd think. But then again, snow, the kind of driving you're doing, will all factor in as well.

Yes, as I recall, you only need the O-ring for the housing not that other paper thing. There should be two bolts on the housing though. When I removed my original aluminum housing from one of my cars, the aluminum had cracked and left a ring behind in the manifold, looked like it was supposed to be there at first glance, otherwise if it's not leaking and it's only slightly out of flat it should be ok.

On the LN3 it actually is just one bolt



Kind of a funny design in all honesty

L27 on was a bit more traditional

Your engine will never run well unless it at its design operating temperature, around 190f. You have an issue with the thermostat, I assume you are using a 180 or higher thermostat?. It sounds as if the thermostat isn't sitting properly in its housing, allowing coolant to bypass it.
Of course there are other factors that can hurt gas mileage, dragging brakes, a bad transmission, crawling along a snow bound road, all of the above will hurt mileage, don't limit your search to just the engine, but get it running at its correct temperature first.

Roger.

rustyroger wrote:Your engine will never run well unless it at its design operating temperature, around 190f. You have an issue with the thermostat, I assume you are using a 180 or higher thermostat?. It sounds as if the thermostat isn't sitting properly in its housing, allowing coolant to bypass it.
Of course there are other factors that can hurt gas mileage, dragging brakes, a bad transmission, crawling along a snow bound road, all of the above will hurt mileage, don't limit your search to just the engine, but get it running at its correct temperature first.

Roger.

Current one in there is a stant 195f t stat .. Brand new brakes and wheel cylinders and calipers. Tranny shifts like butter. Car doesn't misfire.. Runs strong as an ox.. I average about 140-160 miles after a 13 gallon fill up of 89 .. I noticed smoke coming from my egr valve when I used seafoam... Think that can be it?

RJolly87 wrote:On the LN3 it actually is just one bolt



Kind of a funny design in all honesty

L27 on was a bit more traditional

Got 2 of those brand new .. One from gm and one from four seasons.. Still only sits flush with out the t stat gasket

Here is the procedure with pictures from the appropriate application:

http://www.autozone.com/repairinfo/repa ... 3f8038fb62

From what I gather, here is what I would do (or at least try to do):

1. Pull it apart
2. Make sure upper O-ring is good. If so, lube it (I am thinking either straight coolant or a touch of motor oil with your finger should be perfect)
3. Lube the sides of the hole
4. Put rubber gasket in end of thermostat housing so that the recess goes in to the housing itself
5. Stick thermostat in to gasket in housing, with the dome pointing towards the housing, do NOT lube that, because the friction should hold it in
6. Slide the whole thing in to the engine as far as it will go (this is the part that you were lubing for BTW)
7. As long as it is bottomed out on something, and the o-ring is completely in the sleeve, you should be fine, as long as you can get a decent threading on the bolt.

The thermostat should sit just inside the housing and gasket, so if you try and put the thermostat in the engine, and then the housing over it, it may not all fit, which is different than other setups.

Oh wow, after looking at those instructions I just linked to again, it looks like they switch applications half way through the process. So they took apart a Vin C(LN3), and reassembled a Vin L/K(L27/L36).

Yeah, I would stick the thermostat in the gasket, in the housing, and then stick everything with the housing in the block and hope for the best.

Its been a long time... But if memory serves, The thermostat does not have a gasket, its just dropped in, and there should be a flat gasket that sits on it and the thermostat housing sits on top of it.. I could swear I had a hard time getting this seal, Most references don't even list it.. I make no promises it 100% what you need..

Engine Coolant Thermostat Housing Seal Fel-Pro 35126

The thermostat housing is a freaky set up, single bolt design.. Never figured that one out... and don't ever mess with those coolant tubes to the throttle body, you'll be very hard pressed to find another one...

What kind of O2 sensor did you use?

For the best fuel economy you want the engine to run at 180F or better..

Man, it's been so long since I messed with the '89 PA that I could see how it was only one bolt and not two like I was thinking.

But I do recall that there is no paper gasket, only the O-ring for the housing, and that I had to grease and work it into position before it would sit flush.

I'm gonna take pictures. With all parts out the car u can not get any combo of housing/gasket/tstat to fit in the housing..

I have used both a paper gasket and a rubber one in mine. Originally it had a paper one but when i changed it at some point if came with a rubber seal that worked fine and is still in there. the housing may not sit perfectly flush but it won't matter with the rubber seal. the tstat and gasket should be able to be pressed down into the manifold.

Re-check your thermostat part number with an online parts store. It should fit in the
recessed groove with the o-ring gasket on it, unless someone changed the intake on your engine.

It's basic but did you replace the pcv valve?